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抽象灵感的英语作文Title: Unveiling the Essence of Abstract Inspiration。
In the realm of creativity, abstract inspiration serves as the ethereal force that drives artistic expression and innovation. It is a mysterious muse that whispers ideasinto the minds of creators, transcending conventional boundaries and igniting the imagination. Exploring the nature of abstract inspiration unveils a captivating journey into the depths of human creativity.At its core, abstract inspiration defies conventional definition, eluding the confines of logic and reason. It emanates from the subconscious mind, often emerging unexpectedly and evoking a profound sense of wonder. Unlike concrete stimuli, such as tangible objects or specific experiences, abstract inspiration arises from intangible sources, such as emotions, dreams, and the collective unconscious.One of the most intriguing aspects of abstract inspiration is its elusive nature. It cannot be summoned at will or controlled by external forces; rather, it manifests spontaneously, like a sudden burst of light in the darkness. Artists, writers, and innovators alike have long grappled with the enigma of inspiration, seeking to capture its essence and harness its transformative power.In the realm of visual arts, abstract inspiration takes on myriad forms, from the vibrant brushstrokes of apainting to the sculpted contours of a masterpiece.Abstract artists, such as Wassily Kandinsky and Jackson Pollock, have famously explored the depths of the subconscious, allowing their inner visions to guide their creative process. Through abstraction, they transcend the limitations of representation, inviting viewers to delveinto the realm of pure sensation and emotion.Similarly, in the domain of literature, abstract inspiration fuels the imaginations of writers and poets, infusing their words with lyrical beauty and profound meaning. Authors like Virginia Woolf and James Joyce delveinto the inner workings of the human psyche, weavingintricate narratives that defy traditional storytelling conventions. Through stream-of-consciousness prose and experimental techniques, they capture the fleeting natureof thought and emotion, inviting readers to explore the depths of the human experience.Innovation, too, is fueled by abstract inspiration, as visionary thinkers push the boundaries of possibility and redefine the limits of human potential. Scientists and inventors draw upon abstract concepts and theoretical frameworks to envision groundbreaking technologies and paradigm-shifting discoveries. From the revolutionary theories of Albert Einstein to the disruptive innovationsof Steve Jobs, abstract inspiration serves as the catalyst for progress and change.Despite its intangible nature, abstract inspiration is not devoid of structure or meaning. Rather, it existswithin a framework of interconnected ideas and associations, drawing upon the rich tapestry of human experience. Each moment of inspiration builds upon the accumulated wisdom ofthe past, weaving together disparate threads of thoughtinto a cohesive whole.Ultimately, abstract inspiration serves as a reminderof the boundless potential of the human mind. It invites us to embrace uncertainty and embrace the unknown, trusting in the creative process to guide us towards new horizons. By surrendering to the ebb and flow of inspiration, we open ourselves to infinite possibilities, allowing our imaginations to soar beyond the constraints of the familiar.In conclusion, abstract inspiration transcends the boundaries of conventional understanding, serving as a source of creativity and innovation. From the visual artsto literature to scientific discovery, it permeates every aspect of human endeavor, guiding us towards new realms of possibility. By embracing the enigma of abstractinspiration, we embark on a journey of self-discovery and artistic expression, tapping into the infinite wellspringof creativity that lies within us all.。
Translation Strategies for Translating Postmodifiers in Scientific Text from the Perspective of Logic Translation Theory: A Case Study of the Translation of Climate Changeand Air PollutionByZhang XiaojieUnder the Supervision ofAssociate Professor Zheng YouqiSubmitted in Partial Fulfillment of the RequirementsFor the Degree of Master of Translation and InterpretingDepartment of EnglishCollege of Liberal ArtsNanjing University of Information Science & TechnologyJune, 2019AcknowledgementsI would like to express my sincere appreciation to those who have given me invaluable help during the writing of this report.First and foremost, my heartfelt gratitude goes to my supervisor, Associate Professor Zheng Youqi, for his constant encouragement during these two years and instructive advice on this report. Associate Professor Zheng has offered a lot of valuable suggestions during the preparation for the report. He has also revised my draft carefully and offered clear instruction. Without his patient instruction and insightful criticism, it would not have been possible for me to complete this report.In addition, I wish to take this opportunity to express my deep gratitude to all the teachers who have taught me for their patient instructions in many courses and their precious suggestions. What I learned from their classes has helped me lay the foundation for this report.Last but not least, my gratitude extends to my beloved parents for providing support and care for me in my whole life. They have given me strong support when I was confronted with difficulties in writing the report.ContentsAbstract ........................................................................................................................ I II 摘要 (V)Chapter One Introduction (1)1.1 Research Background (1)1.2 Motivation and Significance of the Research (2)1.3 Layout of the Report (3)Chapter Two Task Description (5)2.1 Project Profile (5)2.2 Process of the Project (5)2.2.1 Preparation for Translation (5)2.2.2 Process of Translation (6)2.2.3 Revision after Translation (7)Chapter Three Literature Review (8)3.1 Differences of Attribute between Chinese and English (8)3.2 Translation Strategies for Postmodifier in English. (9)Chapter Four Theoretical Framework (11)4.1 Development of the Logic Translation Theory (11)4.2 Application of the Logic Translation Theory in the Translation of thePostmodifier (12)Chapter Five A Case Study (14)5.1 Translation of the Adjective Phrase as Postmodifier (14)5.1.1 Inversion (14)5.1.2 Division (15)5.2 Translation of the Non-Finite Verb as Postmodifier (16)5.2.1 Inversion (17)5.2.2 Division (18)5.2.3 Amplification (19)5.3 Translation of the Attributive Clause as Postmodifier (20)5.3.1 Inversion (20)5.3.2 Amplification (21)5.3.3 Division (23)5.4 Translation of the Prepositional Phrase as Postmodifier. (24)5.4.1 Inversion (24)5.4.2 Conversion (25)5.4.3 Amplification (25)5.4.4 Division (26)Chapter Six Conclusion (28)References (30)Appendix 1 Source Text and Target Text (32)Appendix II Technical Terms (94)攻读学位期间的研究成果 (95)AbstractThere are many postmodifiers in English for Science and Technology (EST), which imply the logic in the original text. EST is characterized by strong professionalism, compact structure, strict logic, concise writing, objective expression, exact content, a large amount of information and emphasis on the existence of facts. Therefore, translators must restore its logical rigor with accurate and standardized expressions. In this translation task, Chapter One, Chapter Two and Chapter Three are selected as the source text from the book Climate Change and Air Pollution. Today, climate change and air pollution are major concerns around the world. These chapters describe the history and the impact of climate change and air pollution, and the international conferences held to address the problems caused by climate change. This report lists four forms of English postmodifiers from the three chapters, namely, adjective phrases as postmodifiers, non-predicate verb phrases as postmodifiers, attributive clauses as postmodifiers, and prepositional phrases as postmodifiers. Under the guidance of logic translation theory, four common translation strategies are used in the translation of these four kinds of postmodifiers, namely conversion, amplification, inversion and division. Logic plays an important role in the process of interlingual transformation, which runs through the process of translation. From words, sentences, paragraphs to the whole text, the more accurately the translator grasps the semantic logic of the source language, the easier it is to understand the meaning of the original text. When a translation is organized, it is the key to express the original meaning accurately and smoothly. Only in this way can the translator successfully transfer source language thinking to target language thinking, and skillfully use the logic of the target language to organize the translation.The report is divided into six chapters. The first chapter demonstrates the research background, the motivation and significance of the research and the layout of the report. The second chapter mainly describes the process of the project. Theliterature review is mentioned in the third chapter, including the differences of attribute between Chinese and English and the translation strategies of postmodifiers in English. The fourth chapter depicts the development and application of the logic translation theory. The fifth chapter, as the main body of the report, poses some proper translation strategies to solve different kinds of problems. The last chapter is a summary of the study.Key Words: Logic translation theory; Postmodifier; Translation strategy; Climate Change and Air Pollution摘要科技英语中后置定语出现频繁，体现原文的逻辑思维。
英语作文里的逻辑如何体现Logic is an essential component of writing an effective and persuasive essay. It is the backbone of a well-structured essay that presents a clear and concise argument. In this essay, I will discuss how logic is reflected in English writing and provide a high-quality imitation of the most downloaded essay online.Firstly, logic is reflected in the structure of an essay. A well-structured essay follows a logical sequenceof ideas that leads the reader from the introduction to the conclusion. The introduction should provide background information and set the tone for the essay. The body paragraphs should be organized in a logical order that supports the thesis statement. Each paragraph shouldcontain a topic sentence that introduces the main idea and evidence that supports it. The conclusion should summarize the main points and restate the thesis statement.Secondly, logic is reflected in the use of evidence. Apersuasive essay should provide evidence that supports the argument. The evidence should be relevant, reliable, and presented in a logical manner. The writer should use facts, statistics, and examples to support their argument. The evidence should be presented in a logical order that supports the thesis statement.Thirdly, logic is reflected in the use of language. The language used in an essay should be clear, concise, and precise. The writer should avoid using vague or ambiguous language that can confuse the reader. The writer should use words and phrases that are appropriate for the audience and the purpose of the essay. The writer should also use transitional words and phrases to connect ideas and create a logical flow.Now, let me provide a high-quality imitation of the most downloaded essay online, reflecting the use of logicin English writing.The topic of my essay is the importance of exercise for a healthy lifestyle. The essay will follow a logicalstructure that includes an introduction, body paragraphs, and a conclusion. The body paragraphs will provide evidence that supports the argument that exercise is essential for a healthy lifestyle.Introduction:Exercise is an essential component of a healthy lifestyle. It has numerous benefits that include weight loss, improved cardiovascular health, and increased energy levels. In this essay, I will discuss the importance of exercise for a healthy lifestyle.Body Paragraph 1:Exercise is an effective way to maintain a healthy weight. It burns calories and increases metabolism, which helps to reduce body fat. In addition, exercise can help to prevent obesity, which is a major risk factor for many chronic diseases.Body Paragraph 2:Exercise improves cardiovascular health. It strengthens the heart and improves blood flow, which reduces the risk of heart disease and stroke. Regular exercise can also lower blood pressure and cholesterol levels, which are other risk factors for cardiovascular disease.Body Paragraph 3:Exercise increases energy levels and improves mood. It releases endorphins, which are natural mood boosters. Regular exercise can also improve sleep quality, which is essential for overall health and wellbeing.Conclusion:In conclusion, exercise is essential for a healthy lifestyle. It has numerous benefits that include weight loss, improved cardiovascular health, and increased energy levels. By incorporating exercise into our daily routine, we can improve our overall health and wellbeing.。
【工程技术研究与应用】主持:李艳利用遗传算法进行机械优化冯锦春1 杨林建1①(1.四川工程职业技术学院,四川德阳618000)[摘 要] 本文简单介绍了遗传算法的原理和运算过程,讨论了遗传算法在机械优化方面的应用,并用实例加以说明,总结了它的特点和应用前景。
[关键词] 遗传算法;机械;优化中图分类号:TH123 文献标识码:A 文章编号:CK N 字07-005(2007)06-0072-02The Use of Geneti c A lgor ith m i nM ach i n ery O pti m i za ti onFeng J inchun 1 Yang L injian2(1.Sichuan Engineering Technical College,Deyang Sichuan 618000,China )Abstract:This paper si m p ly intr oduces a genetic algorith m theory and computati on p r ocess,discusses the ge 2netic algorith m in the app licati on of mechanical op ti m izati on,using exa mp les t o illustrate .It su m s up the charac 2teristics and app licati on p r os pects .Key words:Genetic algorith m s;mechanical engineering;op ti m izati on 遗传算法模拟了自然选择和遗传中发生的复制、交叉和变异等现象,从任一初始种群(populati on )出发,通过随机选择、交叉和变异操作,产生一群更适应环境的个体,使群体进化到搜索空间中越来越好的区域,这样一代一代地不断繁衍进化,最后收敛到一群最适应环境的个体(indi 2vidual ),求得问题的最优解。
英语抽象类作文模板范文Abstract Class Essay Template。
An abstract class is a concept in object-oriented programming that serves as a blueprint for other classes. It cannot be instantiated on its own and is meant to be extended by other classes. In this essay, we will discuss the characteristics of an abstract class, its purpose, and its role in the development of software applications.An abstract class is a class that cannot be instantiated, meaning you cannot create an object of the abstract class itself. Instead, it serves as a base for other classes to inherit from. It can contain both abstract and non-abstract methods. An abstract method is a method that is declared but not implemented in the abstract class. It is meant to be implemented by the subclasses that inherit from the abstract class. On the other hand, a non-abstract method is a method that has an implementation in the abstract class itself.The purpose of an abstract class is to provide a common interface for its subclasses. It allows you to define a set of methods that must be implemented by all the subclasses, ensuring that they have a consistent behavior. This is useful when you have a group of classes that share some common characteristics but also have their own unique behavior. By using an abstract class, you can define the common methods in the abstract class and leave the specific implementation to the subclasses.Another important role of an abstract class is to provide a level of abstraction in the design of a software application. Abstraction is a fundamental concept in object-oriented programming that allows you to focus on the essential features of an object while hiding the unnecessary details. By using an abstract class, you can define the essential methods and properties that are common to a group of related classes, while hiding the implementation details from the outside world. This makes the design of the software application more modular and easier to maintain.In addition, an abstract class can also be used to enforce a specific contract on its subclasses. By defining abstract methods in the abstract class, you can require that all thesubclasses provide an implementation for those methods. This ensures that the subclasses adhere to a certain set of rules and guarantees a consistent behavior across the different subclasses.To create an abstract class in a programming language such as Java or C#, you use the "abstract" keyword in the class definition. For example, in Java, you would declare an abstract class like this:```java。
第43卷第11期包装工程2022年6月PACKAGING ENGINEERING·46·不可逆温敏变色油墨的显色动力学探究俞胡斐，钱静（江南大学，江苏无锡214122）摘要：目的探究温敏变色油墨对时间、温度的响应情况，以及不同制备配方对其动力学参数的影响。
方法利用光生酸剂的分解反应使结晶隐性紫染料开环显色，以此作为变色体系置于丝网油墨中，制备出可随时间–温度累积进行不可逆变色的智能温敏标签。
利用分光密度仪测量标签b*值，以标签b*值变化作为测量指标，将其与变色时间进行拟合，探讨油墨组分对标签变色性能的影响。
并探究不同组配方下b*值对温度变化的响应，以及不同配方对反应活化能的影响。
结果随着时间的积累，油墨印刷标签b*值逐渐减少，标签颜色由浅黄色变成深蓝色；同时，当温度升高，标签的变色速率也随之加快，温度越高，标签所测量的b*值越低，呈现出的蓝色越深。
相同温度下标签|Δb*|值较高时，标签的活化能较低。
结论该标签对时间、温度的积累均有响应，制备的标签活化能在11.453～27.676 kJ/mol波动，具有应用在食品品质智能监控领域的潜力。
关键词：不可逆变色；活化能；丝网印刷中图分类号：TS871 文献标识码：A 文章编号：1001-3563(2022)11-0046-08DOI：10.19554/ki.1001-3563.2022.11.007. All Rights Reserved.Color Kinetics of an Irreversible Thermochromic InkYU Hu-fei, QIAN Jing(Jiangnan University, Jiangsu Wuxi 214122, China)ABSTRACT: The purpose of this paper is to explore the response of thermochromic ink to time and temperature, and theeffects of different preparation formulas on its kinetic parameters. An intelligent thermochromic label that can discolorirreversibly with time-temperature accumulation was prepared by using the decomposition reaction of photo-acid genera-tor to discolor leucocrystal violet as a color-change system in screen ink. A spectrodensitometer was used to measure thelabel b* value, and make the change of label b* value as the measurement index. Then it was fitted with the discolorationtime to explore the influence of ink components on the discoloration performance of labels. With the accumulation oftime, the label b* value gradually reduced, the label color from light yellow to dark blue; at the same time, when thetemperature increases, the rate of discoloration of the label is accelerated. The higher the temperature, the lower the la-bel b* value measured, and the deeper the blue color presented. And the activation energy of the label is lower when thelabel |Δb*| value is higher at the same temperature. In conclusion, the label responds to the accumulation of time andtemperature, and the activation energy of the prepared label fluctuates from 11.453 to 27.676 kJ/mol, which has the po-tential to be applied in the field of intelligent monitoring of food quality.KEY WORDS: irreversible discoloration; activation energy; screen printing收稿日期：2021–08–03基金项目：国家重点研发计划重点专项（2018YFC1603300）；无锡科技局产业前瞻和关键技术（现代农业）（N20193008）；江苏省苏北专项（SZ–SQ2017049）作者简介：俞胡斐（1997—），女，江南大学硕士生，主攻智能包装。
抽象类英语作文Abstract class is an important concept in object-oriented programming. It serves as a blueprint for other classes to inherit from, but cannot be instantiated on its own. In other words, it is a template that provides a set of common methods and properties for its subclasses to implement. These abstract methods must be defined in the subclasses, making them concrete classes.抽象类是面向对象编程中一个重要的概念。
它充当其他类继承的蓝图，但不能单独实例化。
换句话说，它是一个模板，为其子类提供了一组通用的方法和属性供其实现。
这些抽象方法必须在子类中定义，使它们成为具体类。
One of the key benefits of using abstract classes is to enforce a consistent structure and behavior across multiple related classes. By defining a common set of methods in the abstract class, developers can ensure that all subclasses will have these methods implemented. This can improve code quality and maintainability by promoting code reusability and reducing duplication.使用抽象类的主要好处之一是在多个相关类之间强制执行一致的结构和行为。
Formal derivation of concurrent non-blocking algorithms for real-time systemsConfirmation reportBrijesh Dongol1Contents1Introduction3 2Related Work42.1Foundations (5)Hoare logic and predicate transformers (5)Temporal logic (5)Dynamic logic (5)2.2Non-compositional methods (6)Owicki-Gries (6)UNITY (6)Action systems (7)Modular approach (7)TLA (7)I/O automata (7)2.3Compositional methods (7)2.4Program construction (9)2.5Non-blocking algorithms (9)3Results to date10 Progress for Owicki-Gries (10)Java monitors (10)Refinement rules (11)Latest achievements (11)4Research plan11 Research goals (12)Timeline (12)References1321IntroductionConcurrent programs are difficult to get right and onefinds it hard to trust their validity without a formal proof.There have certainly been examples of errors being uncovered in published algorithms that were previously assumed correct.A variety of formalisms for the verification of concurrent programs have been developed and proof tools that allow verification to be automated are available. However,for complex problems,when the verification does not work,it becomes difficult to judge whether the proof technique or the program itself is at fault. Automated model checking techniques are available where all possible states are scanned for errors.With complex programs however,model checking becomes intractable and suffers from the state-explosion problem.Techniques such as abstraction are required to approximate the program so that we operate on a smaller state space.The success of the model checking then depends on the accuracy of the abstraction.With issues such as these,one might look at the development of correct pro-grams instead,so that verification may be avoided.One such method is that of stepwise refinement where a high level specification that satisfies the require-ments isfirst developed.Via a series of small steps,using correctness preserving refinement rules,the specification is eventually refined to an implementation. The idea here is that at an abstract level programs are less detailed and hence easier to verify.As each refinement is correctness preserving,verifying the va-lidity of the refinement and correctness of the abstract level program is enough to establish correctness of the implementation.Here,the high level specifica-tion must be an abstraction of the implementation,hence,they must satisfy the same requirements.This means that the implementation may not introduce any new behaviour.If for some reason the requirements change,the new behaviour must be introduced at the abstract level and the refinement performed again. Also,these methods are more about proving the validity of refinements rather than providing a calculational method for program construction.Compositional methods of program construction are also available.Here,a program is thought of as consisting of a number of components,each of which implements some part of the given requirements.The idea is that components are smaller and hence easier to verify than an entire system.Each component is described by some specification which allows us to reason about its behaviour without referring to its internal structure.One might even like to maintain a library of components,so that components may be reused whenever necessary. Rules for composing specifications are available,which allow us to compose components without affecting their correctness.A problem with this approach is that when there is a high degree of interaction between processes,compo-nent specifications can become very detailed,but with detailed specifications reusability of components becomes difficult.Also,as leads-to(the main relation used to prove progress)is not compositional,progress properties of individual components can be lost during composition.Another method of constructing correct concurrent programs is that of Fei-jen and van Gasteren which is based on the theory of Owicki and Gries.Here,3we start with an approximation to the solution.Then,requirements are for-malised and added as annotation to this approximation.Code is introduced and modified until the annotation is satisfied.As the annotation represents a program’s proof,a program is in fact built to satisfy its proof.Modifications are motivated by the proof rules of Owicki and Gries and wlp calculations of Di-jkstra.A number of lemmas have also been provided which allows much of the work to be avoided.The method has already been used to derive a number of programs across a wide range of problems.However,the lack of a formal notion of progress in Owicki-Gries has meant that Feijen and van Gasteren have been unable to reason about progress in their derivations.A more detailed discussion is presented in Section3.The problems we would like to consider are non-blocking algorithms oper-ating over a real-time environment.Non-blocking algorithms achieve synchro-nisation by manipulating variables in complex ways,as opposed to using locks. As no process ever waits,non-blocking versions tend to achieve much better efficiency than equivalent lock-based counterparts.Problems such as priority inversion where a high-priority process is waiting for a lock held by low-priority process can be avoided.This is a serious problem in real-time systems where the high-priority process might miss some deadline due to it being unable to acquire a necessary lock.It is worth noting that Owicki-Gries formalism does not currently have a way of reasoning about real-time,but Hooman-van Roosmalen have described the notion of timing annotation which provides clues on how possible exten-sions might be performed.Timing annotation could also allow us to abandon interleaving semantics and examine true concurrency.Ideas such as conflict composition could be applied here which would force transitions to interleave only when they share the same state space.Within the Java2platform,atomic variable classes are available in Java which allows us to implement non-blocking algorithms.As there are already ex-amples of successful derivations of Java programs using the Feijen-van Gasteren approach,one would think that Java implementation of non-blocking algorithms would be the next logical step.One also hopes that life can be made simpler with tool support.The“Improving the Quality of Protocol Standards”project (http://www.win.tue.nl/oas/iqps/two distinct but equally challenging thought processes of coming up with the appropriate set of formal assertions,then using them to establish a set of proof obligations which can be verified.The two key requirements that concurrent programs need to satisfy are safety and liveness[Lam77].This distinction has developed extensively over time,expressed via a number of different viewpoints [Kin94].For instance,[AS85,AS87]shows us how,from a topological viewpoint, safety properties are closed sets and liveness properties dense sets.When think-ing about progress,one must invariably address assumptions about fairness as well.This topic is carefully studied in[Fra86].Correctness conditions like lin-earisability that focus on data(rather than control)have also been deveoped [HW90],which is the main condition used to verify non-blocking algorithms(eg. [DGLM04]).2.1FoundationsHoare logic and predicate transformers One of thefirst coherent meth-ods of proving properties of programs using program text was via Hoare logic [Hoa69].Later,[Dij76]introduced us to predicate transformers with which, one could prove program properties purely by syntactic manipulation.As the method is calculational,predicate transformers proved to be a useful tool not only in verification,but also in program derivation.Hoare logic and predicate transformers were initially developed to prove properties of sequential programs, hence suitable extensions are necessary in the context of concurrency. Temporal logic Temporal logic[Pnu77,MP95],is an extension to classical first order logic,which allowed reasoning about properties that change with time.Temporal logic drives the machinery for proving progress in the same way that Hoare-logic does for safety.Two forms of temporal logic exist-linear time temporal logic(LTL)and concurrent(or branching time)temporal logic (CTL),whose merits are described in[Lam80,EH86].The view taken by LTL is that for each moment,there is exactly one possible future,whereas CTL says that time may split into multiple paths representing the different possible futures.Proofs of temporal formulas without using temporal logic are explained in[AS89],where temporal formulas are translated to Buchi automata. Dynamic logic Dynamic logic(DL)[Har84]is another formalism for reason-ing about programs.DL is expressive enough to be able to give us insights into various program properties like correctness,the expressive power of program-ming constructs,program equality etc.The logic is a mix offirst order and predicate logic,modal logic and process algebras.A concurrent extension can be made[Pel87a,Pel87b,Pel84]where computations are modelled by branching paths.52.2Non-compositional methodsThese methods are classified as those that require complete knowledge of the other components.Owicki-Gries A popular and much referenced method for verification of con-current programs is the theory of Owicki-Gries[OG76]which builds on Hoare’s logic for sequential programs.The method supercedes the previously existing global invariant method of Ashcroft[Ash75]which itself is a concurrent ex-tension to the global invariant method of[Flo67]for sequential systems.The state-explosion problem suffered by the global invariant method is avoided via the interference freedom condition which allows us to decompose invariants so that a number of smaller proof obligations are proved instead.[Lam88]points out that annotations provide a pleasant manner in which verification of large invariants are decomposed into smaller and more localised proofs.The Owicki-Gries method is thought of as being more applicable to shared-memory systems, however,[AO91,FvG99]have shown how communication channels may be mod-elled by shared variables to reason about distributed systems.It is sometimes referred to as the modular method of proving invariants[JHW96].Owicki-Gries does,however,have a crucial deficiency:there does not exist a logic for reasoning about progress.This fact remained true for the derivations in[FvG99]where progress is given an informal operational treatment.Progress for the Owicki-Gries theory is addressed in[DG05]by incorporating the rules of progress of UNITY into the logic.In[GD05]the extended theory is used to derive Dekker’s algorithm in the style of Feijen and van Gasteren,where safety as well as progress are given equal consideration.UNITY UNITY[CM88]takes into account the commonalities in program de-velopment without targeting a specific application or architecture.The theory in UNITY has produced the greatest strides with the axiomatisation of the pre-viously temporal notion of leads-to.However,leads-to is limited as we cannot directly reason about temporal properties such as‘next’and complex manipu-lation of auxiliary variables are necessary to achieve this[Sha93,CK97].Also, there is an absence of control in UNITY,hence existing theories for program development and verification are not applicable[dRdBH+01].It is not easy to introduce operators such as sequential composition[SdR94].[CM88,Kna90a, Kna90b]give us examples of development of programs,ultimately represented in the UNITY framework.The development process consists of stating the requirements as a number of invariants,then refining these invariants until a level of detail is reached where the UNITY program becomes obvious.[GP89] describes the relationship between UNITY and linear temporal logic by show-ing how UNITY might have been obtained as a specialisation of temporal logic and the transition logic of[Ger84].[JKR89]shows that the leads-to operator in UNITY and that of temporal logic are in fact the same.[CK97]extends UNITY to a compositional framework which also explores strongest invariants[Lam90].6Action systems Another important formalism is that of action systems[Bac89, BS89,Bac92a,Bac92b].The model itself very similar to UNITY,however,the theoretical background is radically different.The idea is that when interleaving semantics is employed,the semantics of a concurrent system is no different from a non-deterministic sequential program.Hence,one can use a sequential pro-gram to model a concurrent system.Semantics of action systems are described in a lattice theoretical framework.Action systems have been extended tofit many contexts such as reactive[Bac92b],component based[Ruk03],distributed and shared memory[BS89].Refinements based on transition traces using ac-tion systems is described in[BvW94].[Qiw96]investigates three different types of refinement in the action system framework–global,modular,and composi-tional.Only safety and forward simulation is addressed,however,the author claims that generalisations that allow backwards simulation and progress to be addressed are possible.Modular approach[Sha93,LS92],presents another state transition model with syntactic constructs similar to that of IOAs,but with semantics that follow UNITY.Systems are represented as sets of state variables,initial conditions, fairness requirements and events.The main difference between UNITY and this method is that we are able to specify different fairness assumptions for different actions.This formalism was developed to reason about distributed protocols.TLA TLA or temporal logic of actions is a body of work developed by Lamport [Lam94].[Aba90]provides an axiomatisation of TLA,and[AL93,AL95]shows us how programs can be constructed in a compositional manner.However, it turns out,that the proofs using TLA are not much different to a proof in the other mport himself claims that any proof in TLA can be translated to a proof in any other method,and vice versa.It seems that for verification at least,the difference might just be presentational.The notion of refinement mappings appears in[AL91]which allows us to prove that a lower-level specification implements a higher level one.In contrast to[FvG99,CM88], the TLA approach is to validate refinements rather than incremental derivation.A very good tutorial on TLA appears in[Lad97].I/O automata[LT89]introduces us to the input/output automata(IOA) formalism,which wasfirst developed as a tool for modelling concurrent and distributed discrete event systems.This work has now been extended to model continuous systems[NLV03].Refinement in the context of IOAs is described in [LV95].2.3Compositional methodsComposition consists of building a system out of several smaller components so that the combined effect of the components satisfies the requirements of the7system.This idea wasfirst advocated in[FP78],and has now become a much establishedfield by itself.Such methods are undeniably necessary in order to verify or construct large scale systems.We prefer to treat a component as a ‘black box’so their composition need not refer to program text.Properties of the component are described by its specification.A variety of terms like rely-guarantee[Jon83],assumption-commitment[MC81],and assumption-guarantee [JT96]are used to describe compositional reasoning.We distinguish between the construction of compositional programs and compositional positional programs are programs that are com-positional by nature whereas compositional reasoning involves arbitrary parallel programs and attempts to construct a compositional proof of the program as a whole by considering the individual parts separately.[Lam98]describes why compositional proof techniques in the context of concurrency are to be avoided.[AL93]pins down the conditions under which specifications can be com-posed.As descriptions are entirely at a semantic level and transition traces are observed,no specific language is referred to,which makes the work appli-cable to a number of other approaches.A description of how specifications can be composed is given,followed by a discussion on how an implementation of a specification by another can be proved.This allows the non-cyclical composition principle to be stated which can be used to prove whether the composition of two specifications implements a program.[XdRH97]provides an overview of compositional methods using the rely-guarantee approach and its relation to the Owicki-Gries and assumption-com-mitment approaches,including proofs of soundness and completeness of the sys-tem.Following[Stø90],the paper also outlines how additional information can be added to the specification so that one may reason about deadlock freedom.From[MS00]we learn that leads-to relations are generally not compositional, yet,specific instances of when they are can be ing a notion called progress sets generalised versions of known compositional theorems for leads-to are produced.[CS95,CS96a]explores how a weakest guarantees(wg)property transformer can be defined,which forms a relationship with the guarantees property similar to that of wp to Hoare-triples.This is used in[CC02]to show us how compositional approaches can be used in specification,development and verification of concurrent programs.[DS96]explores compositionality of the ‘to-always’class of progress properties with which limited results are obtained. [Sha98]introduces us to lazy composition,an alternative paradigm to rely-guarantee where proofs of components meeting their expectations are delayed till sufficient detail has been provided to their design.[dRdBH+01,JPZ91,SdR94]shows how we can use transformational design techniques to develop distributed programs.An attempt is made to produce a layered version of the algorithm where each layer is a smaller concurrent program than the original.The layers themselves are conflict composed which means the ordering of statements only matter when the statements are in conflict.From this,using the communication closed layers(CCLs)theorem,an equivalent dis-tributed version is produced.The motivation behind this approach is that layered versions are easier to verify than distributed ones.Decomposition of the8global invariant takes place as proofs focus only on each layer of the program. [JPZ91]presents a framework that combines action systems with CCLs in a way that supports composition.[JZ92]presents a derivation of a complicated algo-rithm for determining minimum weight spanning trees of graphs using CCLs, and provides a good example of how CCLs are useful in derivation of complex systems.2.4Program constructionA survey of popular data refinement techniques and the relationships between a number of different formalisms is given in[dRE96].Traditionally,two types of simulation relations exist–forwards(or downwards)and backwards(or up-wards).Neither relation by itself is complete and to achieve completeness,one mustfind an intermediate system such that there is a forwards simulation from the concrete to the intermediate and a backwards simulation from the interme-diate to the abstract.[LV95]describes how a single relation that captures both forwards and backwards simulation can be constructed.This is done by con-structing a relation that relates concrete states to sets of abstract states.[Bro93] describes a refinement calculus using transition trace semantics which[Din98] advocates as a good basis for the stepwise refinement of parallel programs.The method in[Din98]supports compositional reasoning,local variables,fairness and reasoning about liveness properties.Another way of constructing concurrent programs is by starting out with a coarse-grained solution,where large chunks of the operation is performed atomically,then reducing granularity of code until we can guarantee atomicity of the statements in our implementation machine.This is the approach taken in[FvG99,GD05].People have also looked at ways to algorithmically construct concurrent pro-grams,however,most of these methods are deficient in some way.For example, the algorithm of[MW84]produces programs with a highly centralised archi-tecture and[EC82]produces concurrent programs in a shared memory model, however,a large number of shared variables may need to be accessed atomically, making many programs infeasible.More recently[EH93,AE96]have developed synthesis algorithms to tackle the problems listed above.However,the method in[AE96]is incomplete(solutions are not always found)and although[EH93] always produces a solution adding a new process requires the whole algorithm to be repeated from scratch.[YKB02]describes a method of synthesising Java monitors using an airport ground traffic control system as an example,but this too has problems regarding the complexity of the solution.2.5Non-blocking algorithmsThe idea of non-blocking algorithms was introduced by Lamport[Lam87],and [HW90]defined linearisability,which is the main correctness condition used in non-blocking algorithms.It is generally accepted that non-blocking versions outperform their blocking counterparts(eg.[MS96,FH]).However,the lock9free property alone is not enough to avoid problems such as infinite overtak-ing,for which reason the notion of wait-free algorithms was developed[Her91]. Derivations of non-blocking algorithms in the style of[FvG99]are presented in[Moo02],and[AC05]describes a development of a concurrent non-blocking queue using Event-B.3Results to dateAs the name suggests,this section outlines the work done so far.Progress for Owicki-Gries An early achievement in this project has been the development of a progress logic for the previously incomplete Owicki-Gries theory[DG05].One of the aims here is to make the change as small as possible, so that familiarity with the Owicki-Gries formalism is maintained.Thefirst realisation is that it is impossible to reason about progress without referring to a program’s control state.Hence,we need to introduce a systematic method of labelling the various control points.This is done by labelling each atomic statement with a unique initial label.Thefinal atomic statement of each process is also given a uniquefinal label so that we may reason about termination.We introduce control variables(program counters),modelled on auxiliary variables,which capture control information without influencing a program’s controlflow.Prior to execution of any statement the program counter must be equal to the statement’s initial label,which indicates that control is currently at the statement.Once the statement is executed,the value of the program counter is updated to the initial label of the statement that follows sequentially.To capture the change in a program’s control state,modified wlp rules for labelled statements are introduced.Finally,progress rules from UNITY are modified tofit the Owicki-Gries formalism,so that temporal‘eventuality’properties could be proved[DG05].This work has been submitted to‘Logical Methods in Computer Science’and is currently under review.The main advantage provided by the extension was that it allowed progress considerations to drive program development in the style of[FvG99].[GD05] presents a significant example of this where the extended theory is used to derive Dekker’s mutual exclusion algorithm.Java monitors Another achievement has been the formalisation of Java syn-chronisation commands in the extended Owicki-Gries model.This not only allowed safety and progress properties of multi-threaded Java programs to be verified,but also provided a basis for the development of Java monitors.The derivation procedure consists of two distinct stages.Thefirst is the development of the model using the standard Feijen-van Gasteren approach.As the model would most likely make atomicity assumptions Java is unable to guarantee,a transformation procedure is necessary to translate the program to the model for the Java monitor.This work has been submitted to QSIC05,and serves as10an example of how the Feijen-van Gasteren development method together with the extended Owicki-Gries theory,can be used to develop Java programs.There are many future directions for this work.For example,exception han-dling has not yet been formalised.When an exception does occur,the behaviour of the program changes significantly.Although exception handling does not af-fect our goal of designing correct Java programs,formalising exception handling, would allow us to design programs that catch exceptions correctly.It might also be possible streamline the two stage process in favour of an approach in which Java programs are generated more directly.Here,one would have to derive the algorithm itself with a Java implementation in mind,rather than a derivation followed by a translation.A difficulty would be reasoning about Java’s wait statement which blocks halfway through its execution.Refinement rules Although this derivation style is successful,we might still like to apply traditional refinement techniques such as simulation,a technique that has been used effectively to prove correctness of non-blocking algorithms [DGLM04].With the idea in mind that translation should be avoided when-ever possible,another achievement has been the development of rules to prove simulation.These rules were adapted from other formalisms and hence do not contain anything theoretically new,but has been a useful learning exercise and demonstrates that the Owicki-Gries formalism can be extended with simulation rules.Latest achievements Some advances have been made towards derivations of non-blocking algorithms for concurrent data structures,and reasoning about concurrent real-time systems using timing annotation.Safety and progress proofs in PVS have also been looked at.4Research planAs mention in Section1,the goal for the next two years is to focus on derivations of non-blocking algorithms,in particular,non-blocking algorithms in the context of real-time.To avoid problems such as priority inversion,it looks likely that we will need to focus on wait-free algorithms.[HvR00]describes a refinement model for real time systems where the idea of timing annotation has been introduced.Each atomic transition is associated with an‘execution moment’that records when the effect of the transition was realised.Timing annotation allows us to reason about timing requirements for each statement,i.e.,to check when in time each statement may execute.Failure of programs to satisfy timing requirements may help us introduce new code in the same manner as[FvG99].We might also see the need to extend the progress logic further by providing a basis for the‘next’temporal operator.As it is not part of the UNITY logic,‘next’is also missing from Owicki-Gries extension.With leads-to,one can only show that a property eventually becomes true but not that it becomes true in11the immediate next state.Yet,for wait-free algorithms,identifying the sorts of conditions that are required for‘next’to be true may be useful.Research goals1.Extensions to the Owicki-Gries system:(a)Support for real-time(b)Support for‘next’(c)Complete refinement rules2.Derivations in the style of Feijen and van Gasteren that consider safetyand progress:(a)Real-time algorithms(b)Programs that incorporate‘next’(c)Non-blocking concurrent data structures(d)Wait-free algorithms(e)Implementation in Java3.Tool support for the extensions and derivation process.Non-blocking queueTimeline for2006Timeline for2007This year will be spent tying up any loose ends and writing up the thesis.12References[Aba90]M.Abadi.An axiomatization of Lamport’s temporal logic of ac-tions,1990.[AC05]J.R.Abrial and D.Cansell.Formal construction of a non-blocking concurrent queue algorithm(a case study in atomicity).Journalof Universal Computer Science,2005.[AE96]P.C.Attie and E.A.Emerson.Synthesis of concurrent systems for an atomic read/atomic write model of computation.In Proceed-ings of the5th Annual ACM Symposium on Principles of Dis-tributed Computing,pages111–120,Philadelphia,Pennsylvania,United States,1996.[AL91]M.Abadi and mport.The existence of refinement mappings.Theoretical Computer Science,82(2):253–284,1991.[AL93]M.Abadi and posing specifications.ACM Trans.ng.Syst.,15(1):73–132,1993.[AL95]M.Abadi and mport.Conjoining specifications.ACM Trans.ng.Syst.,17(3):507–535,1995.[AO91]K.R.Apt and E.R.Olderog.Verification of sequential and con-current programs.Springer-Verlag New York,Inc.,1991.[AS85] B.Alpern and F.B.Schneider.Defining liveness.21:181–185, 1985.[AS87] B.Alpern and F.B.Schneider.Recognizing safety and liveness.Distributed Computing,2(3):117–126,1987.[AS89] B.Alpern and F. B.Schneider.Verifying temporal proper-ties without temporal logic.ACM ng.Syst.,11(1):147–167,1989.[Ash75] E.A.Ashcroft.Proving assertions about parallel programs.JCSS, 10:110–135,February1975.[Bac89]R.J.R.Back.Refinement calculus,part II:Parallel and reactive programs.In REX Workshop for Refinement of Distributed Sys-tems,LNCS430.Springer-Verlag,Nijmegen,The Netherlands,1989.[Bac92a]R.J.R.Back.Refinement calculus,lattices and higher order logic.Technical Report CaltechCSTR:1992.cs-tr-92-22,California Insti-tute of Technology,1992.13。
Timed games with branching-time winning conditionsAniello MuranoDipartimento di Informatica ed Applicazioni,Universit`a degli Studi di Salerno,Via S.Allende,84081Baronissi(SA){murano}@dia.unisa.itThe theory of games,traditionally related to the economic-theoretic environment(see for instance [19]),has been attracting the interest of many researchers in both computer science and control theory. The notion of a game naturally arises in the verification of reactive systems and program synthesis [4,21].In the compositional approach,a reactive system is seen as a set of interacting components, each of them is modelled as an open system(that is,a system whose behaviour depends on the current state as well as the behaviour of the environment in which it is embedded).The interaction between a component and the rest of the system,or the interaction between a controller and the related plant, both can be modeled as a two-player game.For verifying closed systems,where a system behaviour is completely determined by the current state,model-checking is a very successful technique[6,7,8]. The equivalent of model-checking for open systems is checking for the existence of a winning strategy, according to a given winning condition,in a two-player game[15].In this paper we focus on the verification of open real-time systems,modeled as nondeterministic timed automata[2]:finite automata augmented with afinite set of real-valued clocks.The transitions of a timed automaton are enabled according to the current state,that is,the current location and the current clock values.In a transition,clocks can be instantaneously reset.The value of a clock is exactly the time elapsed since the last time it was reset.A clock constraint(guard)is associated to each transition with the meaning that a transition can be taken only if the associated guard is enabled.A clock constraint(invariant)can also be associated to each location with the meaning that the automaton can stay in a location as long as the corresponding invariant remains true.When interpreting a nondeterministic timed automaton as a(timed)game graph,we capture the choices of the protagonist by the symbols associated with the transitions and nondeterminism is used to model the possible choices of the antagonist.To model the case that the protagonist stays idle and the antagonist is moving,we use a special symbol denoted byξ.The case that both players stay idle is captured by letting time elapse in a location.A play of a timed game is thus constructed in the following way.At each time,a player declares the time it will wait idling,along with its next choice. At the time one of the players or both move,both players are allowed to redeclare their next move and the time they will issue it.Technically,a play is a run of the automaton modeling the game.A game is given by a game graph along with a winning condition that establishes which computations are winning for the protagonist.In this paper we solve Ctl and Tctl games,that is,timed games with1a winning condition given,respectively,by a formula of the branching-time temporal logic Ctl[6],or its real-time extension Tctl[1].C tl Timed Games.A way to decide discrete games is to reduce them to the emptiness problem for tree automata(see,for example[22]).Here,we extend the automata-theoretic approach to solve Ctl timed games.Given a timed game(G,ϕ),where G is a game graph andϕa Ctl formula, we construct a tree automaton A G that accepts all theω–trees corresponding to a strategy of the protagonist.We construct this automaton exploiting the clock region relation[2].Then,we construct another tree automaton Aϕaccepting all the trees satisfying the property expressed byϕ.Since strategies of the protagonist correspond to trees accepted by A G,to construct Aϕwe only need to capture models with arity bounded above by the arity of A G(i.e.the maximum branching degree of A G transitions).Thus,there exists a winning strategy of the protagonist in the game(G,ϕ) if and only if the intersection between the languages accepted by A G and Aϕis not empty.Since the size of Aϕis exponential in the size ofϕ[25],checking the emptiness for a B¨u chi tree automaton is polynomial in the number of its states[26],and the intersection of the languages accepted by A G and Aϕis accepted by a B¨u chi tree automaton whose number of states is exponential in the number of states of A G and Aϕ[23],we obtain an algorithm that takes exponential time.Since timed reachability games are known to be Exptime-hard[14],we have that our result is complete.T ctl Timed Games.The syntax of Tctl is given by augmenting the temporal operators of Ctl(except for the“next”,which is discarded since it does not have a clear meaning in a dense time domain)with a timing constraint of type≈c,where≈is one among<,≤,>,≥,and=,and c is a natural number.While Ctl allows to express qualitative temporal requirements on the occurrence of events,with Tctl it is also possible to express quantitative requirements.For example,using Ctl we can express assertion like“p1is true until p2is true”,but we cannot express assertion like“p1is true until p2is true within time2”,which can be expressed in Tctl.In Tctl timed games,thus,we allow dense real-time in both the game graph and the winning condition.Model-checking of Tctl-formulas is Pspace-complete while checking for their satisfiability is undecidable[1].In a recent paper,the satisfiability of Tctl is proved to be Exptime-complete if equality is not allowed in timing constraints of the formulas[16].Here we obtain the same complex-ity/decidability result for games.We prove that Tctl games are Exptime-complete,if equality is not allowed in timing constraints.Our approach to solve Tctl games relies on a reduction to the emptiness problem of timed B¨u chi tree automata.Given a timed automaton G and a Tctl–formula ϕ,we solve the game(G,ϕ)by constructing two timed B¨u chi tree automata:A G and Aϕ.The auto-maton A G accepts,for each strategy F of the protagonist,a timedω-tree which is“embedded”into F.The automaton Aϕaccepts instead all the models ofϕwith arity bounded above by the arity of G.By the known results on timed B¨u chi tree automata[17],the intersection of A G and Aϕis still a timed B¨u chi tree automaton,and accepts all the trees that satisfyϕand are embedded into a strategy.Thus,a timed game G admits a winning strategy with respect to a formulaϕif and only if the language accepted by the intersection automaton is not empty.Denoting the product of the sizes ofϕand G by K,we have that the number of states of the intersection automaton is exponential in K while the size of its clock constraints is linear in K.Since checking the emptiness for a timed B¨u chi tree automaton is polynomial in the number of states and exponential in clock size[17],we obtain an algorithm that takes exponential time.The result we obtain is tight,in the sense that Tctl games2are Exptime-complete(hardness is a consequence of the Exptime-hardness of the reachability timed games[14]).Finally,by allowing equality in the timing constraints,Tctl games turns out to be undecidable. It is possible to prove this result by reducing the satisfiability problem of Tctl–formulas,which is known to be undecidable[1]to our problem.Another approach to prove this result is to introduce the module-checking problem of Tctl–formulas in dense real-time,and prove that this problem is undecidable when equality is allowed in the timing constraints[18].Here,the proof is obtained by reducing the problem of deciding whether a nondeterministic two-counter machine has a recurring computation(this problem is known to beΣ11-hard[12]).Games have been studied in the context of discrete,timed,and hybrid systems(see[5,13,21,24]. In literature,different formulations of games with winning conditions expressed by temporal logics have been considered.In[3],alternating temporal logic is introduced.In[15]the model checking of open systems(module checking)is studied.This problem turns out to be Exptime-compete for specification given by Ctl-formulas and2Exptime-complete for specification given by Ctl*-formulas. Rectangular hybrid games with winning conditions expressed by Ltl formulas were solved in[13].In [9],the controller synthesis of timed automata with linear-time specifications given also as timed automata is addressed.Finally,in[10]an automata-theoretic approach to solve Ltl timed games is also considered.Acknowledgments.This abstract contains results obtained during my Ph.D.studies and have been obtained in collaboration with other researchers that I would like to thank:Moshe Vardi, Marherita Napoli,Salvatore La Torre,Marco Faella.References[1]R.Alur,C.Courcoubetis,and D.L.Dill.Model-checking in dense rmation andComputation,104(1):2–34,1993.[2]R.Alur and D.L.Dill.A theory of timed automata.Theoretical Computer Science,126:183–235,1994.[3]R.Alur,T.A.Henzinger,and O.Kupferman.Alternating-time temporal logic.In Proc.of the38thIEEE Symposium on Foundations of Computer Science,pages100–109,1997.[4]M.Abadi,mport,and P.Wolper.Realizable and unrealizable specifications of reactive systems.In Proc.of the16th Intern.Colloquium on Automata,Languages and Programming,ICALP’89,LNCS372,pages1–17,1989.[5]E.Asarin,O.Maler,A.Pnueli,and J.Sifakis.Controller synthesis for timed automata.In Proc.IFAC Symposium on System Structure and Control,pages469–474.Elsevier,1998.[6]E.A.Emerson and ing branching-time temporal logic to synthesize synchronizationskeletons.Science of Computer Programming,2:241–266,1982.[7]E.M.Clarke,E.A.Emerson,A.P.Sistla.Automatic verification offinite-state concurrent systemsusing temporal-logic specifications.ACM Transactions on Programming Languages and Systems,v.8,2:244-263,19863[8]E.M.Clarke,puter-aided verification.IEEE Spectrum,v.33,6:61–67,1996[9]D.D’Souza,P.Madhusudan.Timed control synthesis for external specifications.In Proc.of the19th Annual Symposium on Theoretical Aspects of Computer Science,(STACS’02),LNCS2285:571–582,2002.[10]M.Faella, Torre,and A.Murano.Automata-theoretic decision of timed games.In Proc.of the3rd International Workshop on Verification,Model Checking,and Abstract Interpretation,VMCAI 2002,LNCS2294,pages94–108.Springer-Verlag,2000.[11]M.Faella, Torre and A.Murano.Dense Real-Time Games.Proc.of the Seventeenth AnnualIEEE Symposium on Logic in Computer Science(LICS02),pages167–176,2002.[12]D.Harel,A.Pnueli,J.Stavi.Propositional Dynamic Logic of Regular Programs”,In Journal ofComputer and System Sciences,26:222-243,1983[13]T.A.Henzinger,B.Horowitz,and R.Majumdar.Rectangular hybrid games.In Proc.of the10thInternational Conference on Concurrency Theory,CONCUR’99,LNCS1664,pages320–335,1999.[14]T.Henzinger and P.Kopke.Discrete-time control for rectangular hybrid automata.TheoreticalComputer Science,221(1–2):369–392,1999[15]O.Kupferman and M.Y.Vardi.Module checking.In Computer Aided Verification,Proc.Eighth Int.Workshop,LNCS1102,pages75–86.Springer-Verlag,1996.[16] Torre and M.Napoli.A decidable dense branching-time temporal logic.In Proc.of the20th Conference on the Foundations of Software Technology and Theoretical Computer Science, FSTTCS’00,LNCS1974,pages139–150.Springer-Verlag,2000.[17] Torre and M.Napoli.Timed tree automata with an application to temporal logic.ActaInformatica,38(2):89–116,2001.[18]A.Murano and M.Vardi.Real-time module checking.Work in progress.[19]J.Von Neumann and O.Morgenstern.Theory of Games and Economic Behavior.Princeton Uni-versity Press,1944.[20]A.Pnueli.The temporal logic of programs.In Proc.of the18th IEEE Symposium on Foundationsof Computer Science,pages46–77,1977.[21]A.Pnueli and R.Rosner.On the synthesis of a reactive module.In Proc.of the16th ACM Symposiumon Principles of Programming Languages,pages179–190,1989.[22]M.O.Rabin.Automata on infinite objects and Church’s problem.Trans.Amer.Math.Soc.,1972.[23]W.Thomas.Automata on infinite objects.In J.van Leeuwen,editor,Handbook of TheoreticalComputer Science,volume B,pages133–191.Elsevier Science Publishers,1990.[24]W.Thomas.On the synthesis of strategies in infinite games.In Ernst W.Mayr and Claude Puech,editors,12th Annual Symposium on Theoretical Aspects of Computer Science,STACS’95,LNCS 900,pages1–13.Springer-Verlag,1995.[25]M.Y.Vardi and P.Wolper.Automata-theoretic techniques for modal logics of programs.Journal ofComputer and System Sciences,32:182–211,1986.[26]M.Y.Vardi and P.Wolper.Reasoning about infinite rmation and Computation,115:1–37,1994.4。
艺术和科学的结合例子英语作文Art and science are often seen as two different ends of a spectrum, with art being the creative expression of human emotions and experiences, and science being the systematic study of the natural world. However, in reality, the two disciplines are not as separate as they may seem. In fact,art and science are often integrated in various ways, and their combination can create innovative and impactful outcomes.One example of the integration of art and science is in the field of medical illustration. Medical illustrators use their artistic skills to create accurate and detailed visual representations of complex biological processes, anatomy, and medical devices. These illustrations serve as valuable tools for both researchers and healthcare professionals, allowing them to better understand and communicate complex scientificconcepts. By combining art with science, medical illustrators play a crucial role in advancing medical knowledge and improving patient care.Another example of art and science integration is foundin the field of bio-inspired design. This interdisciplinary approach combines principles from biology and engineering to develop innovative solutions inspired by nature. For instance, engineers and designers often look to the natural world for inspiration when developing new products and technologies, such as biomimetic materials, structures, and mechanisms. By studying the intricate designs and processes found in living organisms, scientists and artists can collaborate to create more sustainable and efficient solutions for various industries.Furthermore, art and science are integrated in the emerging field of data visualization. Data visualization involves using visual elements such as charts, graphs, andinteractive interfaces to communicate complex information and patterns in data. Designers and researchers often work together to create visually engaging and informative representations of scientific data, making it easier for others to understand and interpret the information. Through creative and thoughtful design, data visualization can turn abstract data into compelling stories and insights, bridging the gap between science and the public.In addition, art and science come together in the field of digital media and interactive technology. Artists and technologists collaborate to create immersive experiences, interactive installations, and digital artworks that explore scientific concepts and provoke thought and emotion. By combining artistic expression with technological innovation, these works push the boundaries of both art and science, offering new perspectives and engaging the public in meaningful ways.Overall, the integration of art and science offers endless possibilities for creativity, discovery, and impact. Whether it's through medical illustration, bio-inspired design, data visualization, or digital media, the combination of art and science has the power to transform how we perceive and understand the world. As society continues to evolve,it's important to recognize and celebrate the dynamic synergy between art and science, and the potential it holds for shaping a brighter future.。
Industrial Construction Vol.52,No.1,2022工业建筑㊀2022年第52卷第1期㊀47㊀脆弱的联盟论复杂性建筑与复杂性科学的关系周官武(石家庄铁道大学建筑与艺术学院,石家庄㊀050043)㊀㊀摘㊀要:在放弃解构论述后,复杂性建筑转而寻求与复杂性科学结盟,形成以非线性算法生成为核心,更加精确㊁严格的设计体系,以此突破现代主义建筑范式的形式语言和设计方法束缚㊂通过对这一联盟始终面临的过分迎合时尚潮流和商业文化㊁实施过程中的妥协对 复杂性 的破坏㊁逻辑与现实的必要性等问题的论述,进而分析了复杂性科学作为城市空间基本元素在建筑研究中的适用性,据此认为,复杂性建筑与复杂性科学的联盟并不稳固,与复杂性科学结盟看似提高了复杂性建筑的科学成色及其创作中科学判断的比重,但作为社会产物的建筑终究无法脱离价值判断,否则就必然会损害建筑的适用性㊂㊀㊀关键词:复杂性建筑;复杂性科学;方法论;联盟㊀㊀DOI :10.13204/j.gyjzG21040811The Fragile Alliance On the Relation Between ComplexityArchitecture and Complexity ScienceZHOU Guanwu(School of Architecture and Art,Shijiazhuang Tiedao University,Shijiazhuang 050043,China)Abstract :After abandoning Deconstructivism,complexity architecture turned to seek alliances with complexity scienceto form an exact and rigorous design system with nonlinear algorithm generation as the core,so as to break through themodernism architectural paradigm.Through discussion on the problems that the alliance has always faced such as catering to fashion trends and business culture,destroying complexity due to compromise in the process ofimplementation,the necessity of logic and reality,the applicability of complexity science in the research of architecture as basic element of urban space were analyzed.Based on that,the alliance between complexity architecture andcomplexity science was considered to be not stable.The alliance with complexity science seemed to increase the scientific quality of complexity architecture and the proportion of scientific judgment in its creation,however,architecture as a social product could not be separated from value judgment,otherwise it would inevitably damage theapplicability of architecture.Keywords :complexity architecture;complexity science;methodology;alliance作㊀㊀者:周官武,男,1971年出生,硕士,副教授㊂电子信箱:451147901@ 收稿日期:2021-04-08㊀㊀当下,西方发达国家的基础设施建设已进入缓慢发展的阶段,规模宏大的中国基础设施建设则方兴未艾,看似南辕北辙的两种现象却共同成就了一个风口,为建筑的去实质化提供了广阔市场㊂建筑创作以创新名义挣脱 适用性 的约束,在发明空间之路上突飞猛进㊂为了更多㊁更快地发明空间,建筑学全力发明着概念,并不断从外部引进更多概念㊂其中,复杂性建筑的贡献尤其令人眼花缭乱,解构㊁非线性㊁涌现性㊁褶子,诸如此类为晦涩建筑形式做注脚和背书的晦涩概念,多来自同一个源头 复杂性科学㊂1㊀当代建筑的理论匮乏焦虑自从现代建筑运动将创造性确定为核心价值,建筑学便丢掉了按图索骥的工匠式传统,高度依赖理论的注解和支持,因而经常性陷入理论匮乏引发的焦虑㊂现代建筑运动确立的现代建筑范式是理论与实践的综合体系,以哲学严格性和社会责任感著称㊂在现代建筑范式支持下,建筑师只需依循柯布西耶㊁密斯开创的传统,聚焦效率与服务,不必为寻求新理论而困扰(图1[1])㊂然而,现代建筑范式的形式语言是相对固化的,48㊀工业建筑㊀2022年第52卷第1期图1㊀多米诺体系Fig.1㊀The structure system of Domino商业文化却要求形式不断花样翻新来刺激公众的感官,藉以推动消费的增长㊂作为建筑创作主体的建筑师无法无视商业文化的驱策而永久托庇于现代建筑范式羽翼之下㊂他们不得不尝试跳出现代建筑范式的安全区,探寻新的建筑形式语言㊂问题是,瞬间的范式脱离只需灵光一现,但要另辟天地,就必须夯实逻辑基础,构建与现代建筑范式相仿的可靠理论台地㊂因此,相对历史上任何时期的建筑,当代建筑都更加渴求理论来提供认识论和方法论㊂但建筑界往往怯于理论思考,这使建筑学的理论产出总是无法满足自身需求,不得不经常求诸外部,从其他人文社会学科和自然科学中寻觅理论引擎㊂复杂性建筑与复杂性科学的结盟正是在这种情况下发生的㊂2㊀复杂性建筑与复杂性科学的联盟复杂性科学于20世纪80年代兴起,先后经历了埃德加㊃莫兰学说㊁普利高津引领的布鲁塞尔学派以及圣塔菲研究所的理论三个发展阶段,包括协同论㊁突变论㊁混沌理论㊁分形理论等一系列理论㊂复杂性科学以复杂性系统为研究对象,揭示了复杂性的广泛存在及其非线性㊁不确定性㊁自组织性㊁涌现性特征㊂其超越还原论的方法论,颠覆了传统的还原论研究范式,是分析处理复杂性事物的强大工具㊂所以,兴起不久,其影响即溢出自然科学领域,向哲学㊁社会科学等领域全面渗透[2]㊂复杂性建筑同样发端于20世纪80年代,解构建筑是其早期发展阶段,代表人物如艾森曼㊁屈米等大多受德里达解构理论影响㊂解构建筑并不标榜复杂性㊁非线性,更关切从价值论角度对整体性㊁结构进行颠覆㊂但解构建筑与后期复杂性建筑之间有明显的传承关系,而且其形态已经很复杂,有些作品甚至开始部分借助计算机非线性算法生成建筑形态,表现出一定的非线性特征[3]㊂20世纪90年代,复杂性科学的影响开始波及建筑学领域,复杂性建筑进入后期发展阶段㊂曾经的解构派领袖艾森曼这时候对解构失去了兴趣,开始大谈非线性㊂一度对解构建筑持严厉批评态度的查尔斯㊃詹克斯,也转而称赞解构建筑蕴含的复杂性,并预言非线性建筑运动即将到来[4]㊂复杂性科学为建筑的发展带来巨大的想象空间,计算机科学的飞速发展则使想象的落实成为可能㊂随着计算机模拟复杂系统技术的成熟,通过非线性算法生成复杂建筑形式不再遥不可及㊂格雷格㊃林恩㊁蓝天组等前卫建筑师敏锐地认识到其中蕴含的机会:一种颠覆性的设计方法及其一体化形式语言成为可能㊂他们开始积极寻求复杂性科学的指导,将非线性生成置于设计方法的核心,从而突破了现代建筑还原论方法的束缚,同时孕育出一种颠覆现代建筑语言的生成性形式语言,刷新了有序与无序㊁整体与局部等基本形式问题的认知㊂后期复杂性建筑对更复杂的非线性生成工具的渴求永无休止,这推动着算法生成工具不断发展完善,参数化设计正是在此基础上逐渐成熟㊁流行起来㊂当今天的建筑师通过参数化设计创造各种奇异形体或表皮时,他们或许只是追求视觉冲击,未必会深究设计工具与复杂性科学的关系,甚至意识不到自己采用的设计方法和形式语言是复杂性建筑实践的组成部分,而这恰恰证明复杂性建筑的思想和方法已深入人心㊂从早期到后期,复杂性建筑经历了重大理论变化,解构理论为复杂性科学所替代,价值论换成了科学论,科学主义对人文主义再次取得胜利[5]㊂这并不令人意外,一则,引进科学范式提高 科学 成色是建筑学的长期传统,况且作为最前沿科学理论,复杂性科学还自带时尚光环;二则,解构理论不仅存在逻辑问题,更无法解决设计方法问题,关键的概念 形式转化完全依赖主观理解和想象㊂而基于复杂性科学发展出的非线性生成设计方法可以确保概念 形式转化的严格性和精确性㊂最后也是最关键的,作为一种价值理论,解构理论却无法为复杂性形式提供有力的价值论证,逻辑上很难令人信服㊂所以,当复杂性科学揭示出复杂性的机理,西方建筑界从中看到了摆脱价值论困扰的希望,便无暇顾及复杂性科学是否适用于建筑,急匆匆宣布复杂性建筑投入复杂性科学麾下: 我们获得了第一个后基督教的新型综合世界观,一个能使科学家㊁理论家㊁建筑师㊁艺术家以及普通民众联合起来的结合点㊂它是由所谓 复杂性科学 阐明的新世界观㊂ [3]3㊀并不稳固的联盟拥有纯正科学血统的复杂性科学也是当今最富魅力的时尚题材,混沌㊁分形㊁非线性㊁蝴蝶效应之类术语掺杂在影视文艺作品中,使复杂性科学成为 一个专业人士与非专业人士,科学家与公众,既复杂又有吸引力的结合点㊂ [6]复杂性建筑与之结盟,方方面面皆大欢喜,建筑界得到新理论㊁新方法,公众得以满足时尚需求,商业文化则捕捉到一个可供长期炒作的消费热点㊂但问题是,这一维系专业群体㊁科学理论㊁流行文化㊁商业需求的纽带是否足够坚韧?第一个必须面对的问题是,公众对复杂性科学的热情有多少出自真正的科学认知和兴趣,又有多少出自被流行文化扭曲的浪漫想象㊂肤浅且变动不居的流行口味赋予的荣耀是廉价的,即使复杂性建筑可以分享复杂性科学的这份荣耀,但得到的支持也是不深刻㊁不持久的㊂第二个更为关键的问题是,复杂性科学是否能够在复杂性建筑中真正兑现㊂早期复杂性建筑多不具备足够 复杂性 ,如弗兰克㊃盖瑞的迪士尼音乐厅(图2[7])㊁艾森曼的辛辛纳提阿罗诺夫中心㊁李伯斯金的柏林犹太人纪念馆,已经被今天的评论家开除出 非线性建筑 ,尽管 它们部分地通过计算机非线性的方法生成出来 [8]㊂图2㊀迪士尼音乐厅Fig.2㊀Walt Disney Concert Hall后期复杂性建筑的非线性特征普遍更加鲜明[8],如格雷格㊃林恩的胚胎住宅(图3a[9]㊁图3b[10])㊁蓝天组的云状建筑(图3c[11])㊂这些作品大量使用数字化设计技术进行生成,具有典型的非线性空间形态,理论上的确很符合复杂性科学的标准㊂不过建筑最终得落实到现实空间㊂一旦进入实施环节,正如徐卫国教授指出的,那些基于非线性生成的建筑方案,如FOA的日本横滨国际码头(图4a[12])㊁扎哈㊃哈迪德的广州歌剧院(图4b[13]),蓝天组的大连国际会议中心(图4c[14]),都不得不向技术妥协,以大量平面转折寻求复杂曲面的近似效果㊂[8]非线性生成设计方法确实非常有吸引力,它使建筑形式的自动生成一定程度上成为可能,无须全程依赖人的控制㊂建筑师可以借助Wavefront㊁a㊁b 胚胎住宅;c Paneum中心㊂图3㊀复杂非线性建筑Fig.3㊀Complex nonlinear buildingsa 横滨国际客运码头;b 广州大剧院;c 大连国际会议中心㊂图4㊀基于非线性生成的建筑Fig.4㊀The architecture based on nonlinear generation Rhino等大型3D软件模拟各种力场的复杂相互作用,建构复杂性动力系统,只需改变一些系统参数即可引发系统的自组织演化㊂软件以动画呈现系统演化带来的几何形变,动画的瞬间定格即可得到原始的建筑形式,也即所谓的 动画形式 [15]㊂但在当前技术条件下,复杂性的真正兑现还局限于计算机内的生成过程,动画定格为 动画形式 的瞬间,生成便终结了,不确定性随之消失,得到的只是生成过程的片段和遗迹,自然也无法如詹克斯所期待的那样运动起来,与人共生,反映宇宙发生的过程㊂[3]而且,动画形式只是纯粹的几何形式,生成过程中悬搁脆弱的联盟 周官武49㊀的材料㊁工艺等建构问题依旧离不开人为干预㊂接下来的营建过程,需要确定技术保障下的确定形式㊁确定结构,只能拼凑线性部件 伪装 非线性㊂总体来看,复杂性建筑在形式生成初期阶段,在非线性生成过程确实比较严格地遵循着复杂性科学,但也仅限于此了㊂第三个问题,复杂性科学向建筑领域的全面渗透,并被复杂性建筑奉为圭臬是否具备逻辑和现实的必要性㊂有些学者认为,现代建筑范式只是工业社会的空间方案,而今天的社会则是所谓 后工业化信息社会 ,注定要将基于数字化技术的非线性建筑推向核心位置[16]㊂那么,信息社会与工业社会的空间需求是否有本质不同?信息时代确实带来一些新的空间需求,但这些新需求是否是现代建筑范式无法应对的?如果能够应对,为什么还要在资源危机频发的情况下,以如此巨大的代价寻求一个更复杂,却不能带来太多福利的解决方案?20世纪90年代以来,数字化依赖确已逐渐形成㊂但全面的数字化生存仍只存在于科幻作品之中,现实的数字化则寄居在现代建筑空间之内,并没有表现出明显的适应㊂或许现代建筑范式无法满足信息社会特有的空间需求,但还不足以引发现代建筑范式的崩溃㊂复杂性建筑依旧无法成为主流范式,离核心位置还远得很㊂所以,让人不得不怀疑:以复杂性科学为基础重塑建筑学,到底是出于现实的需要,还是为了给建筑学涂抹更多的科学装饰色,顺带解救陷入理论焦虑的建筑共同体?复杂性建筑从复杂性科学大量吸收规则㊁工具和方法,自觉接受后者的规定,并因此越来越依赖计算机技术,大量进行进行虚拟设计和仿真㊂复杂性建筑在解构建筑阶段曾激烈反对现代建筑的机械论,而今却彻底离不开机器,比异化的现代建筑更加异化了㊂非线性生成是复杂性建筑设计方法的核心,也是复杂性建筑从复杂性科学得到的最大馈赠㊂其实质是虚拟系统的自组织过程,对人而言则是一个 黑箱 ,可以排除价值判断和隐喻,保证生成形式的绝对抽象性㊂不过,即使是最狂热的复杂性建筑派也不敢完全信任计算机,他们会设计和选择算法,再通过反复输入输出寻求理想方案,其结果就是 黑箱 不黑,自组织滑向他组织㊂在现实面前,复杂性建筑与复杂性科学的联盟总是这么摇摇晃晃,把方法论逻辑搞得支离破碎㊂在与复杂性科学结盟后,复杂性建筑就经常脱离现实的轨道:无视人的需求和资源禀赋对建筑的规定性,一味追求 复杂性 ;排斥人对建筑天然拥有的干预控制权利,为计算机算法生成让路;无视建筑的人文属性,清除价值判断,诸如此类㊂归根结底,复杂性建筑并非出于建筑的现实和逻辑需要选择理论,而是预先选择理论,再裁剪现实以服从理论㊂但现实并不会真的服从理论,所以复杂性建筑必然要陷入两难困境:如果坚持复杂性科学逻辑就会在现实面前不断碰壁,如果向现实妥协又会违背复杂性科学逻辑,令两者的联盟变得脆弱不堪㊂4㊀复杂性科学是否适用于建筑建筑是否复杂到必须采用复杂性科学来进行研究,对于复杂性建筑与复杂性科学的联盟来说,这是一个根本性问题㊂建筑界对建筑的复杂性有两种不同理解㊂其一为文丘里所谓的复杂性,产生于大量堆积的样式符号的多层次意义纠缠,空间本身并不复杂㊂这是一种建筑意义的复杂性,用詹克斯喜用的 双重编码 来表达或许更准确[4]㊂其二为建筑本体的复杂性,如复杂性建筑的复杂性,表现为抽象几何形式构成的复杂空间关系,不附加外部意义或隐喻㊂由于意义的理解主观性太强,前者很容易导向无视建筑自身规律的形式主义游戏,而后者着眼建筑本身,逻辑要严密得多㊂但必须指出的是,复杂性建筑的复杂性由复杂性科学定义,不同于一般意义上的建筑本体的复杂性㊂这就带来一个问题:作为有限尺度的空间单位和更大尺度空间系统的构成元素,建筑是否具备这样的复杂性㊂ 在宏观的空间㊁时间尺度上,在建筑和城市的统一体中的确存在非线性㊁突变㊁混沌㊁自相似性的性质㊂ 它们真的能够在一个单体建筑上全部展现出来吗? [6]詹克斯曾经提出过一种缩微宇宙论,主张建筑必须追随科学尤其是复杂性科学, 表现宇宙发生的基本规律 自组织㊁突变以及向更高或更低层次的跃迁 [3]㊂ 建筑的下一个挑战是如何创造真正给能够运动的局部,使居住者或参观者与建筑建立共生关系,积极反映宇宙发生的过程㊂ [3]这一理论将建筑看作宇宙的同构缩微模型,与凯文㊃林奇在古代城市中发现的 宇宙模式 颇为相似,其内在逻辑也与 宇宙模式 一样充满神秘主义色彩[17]㊂詹克斯并不能证明建筑与宇宙间存在自相似性,或具有宇宙式的 复杂性 ,却强行要求建筑套用宇宙图式㊁提高复杂度,以便与复杂性科学相匹配㊂这样得到的建筑并不能反映宇宙,充其量是对宇宙的静态50㊀工业建筑㊀2022年第52卷第1期的㊁图式化的隐喻[6]㊂复杂性 并非元素的属性,而是系统对元素进行组织和整合的产物,是在系统整体层次上涌现出来的东西㊂ [18]因而,作为大空间系统的城市,或大规模聚落㊁城市区段表现出高度复杂性并不出人意料㊂早在复杂性科学影响建筑与城市研究领域之前,简㊃雅各布斯和克里斯托弗㊃亚历山大等学者对此就有深入阐述,复杂性科学则帮助我们对城市空间复杂性的认识更加精确㊁严格㊂但单体建筑只是城市空间系统的元素或局部,不具备系统整体才能具备的复杂性,赋予城市空间复杂性的自然与社会因素的复杂相互作用,及其历时性演化并不存在于建筑单体层面㊂[19]建筑的核心问题始终是适用性问题,即基于资源禀赋和人的需求,对经济㊁技术㊁功能及形式等各方面加以综合㊁平衡的问题㊂这些问题显然不是复杂性科学所能应对的㊂所以,复杂性科学对建筑的影响几乎从未超越形式层面㊂复杂性建筑推进了建筑形式和形式生成方法的革新,却并未提高建筑的适用性,反倒经常因为过度追求形式的复杂性而牺牲经济㊁技术和功能各方面的合理性㊂这不是作为科学工具的复杂性科学本身的问题,而是在非适用领域滥用科学工具造成的问题㊂复杂性建筑追随复杂性科学很大程度上是为了摆脱现代建筑范式的束缚㊂现代建筑强调功能与效率,反对任何非必要的空间㊁形式复杂化㊂这样或许会损害多样性,但对建筑的认知并无原则性问题㊂其真正问题在于过度推崇简约化,试图在本质复杂的城市层级上消灭复杂性㊂而复杂性建筑正相反,以复杂性为目标,不分单体建筑还是大规模空间系统㊂藉此固然可以跳出现代建筑范式的樊笼,却也同时迷失了面向建筑的问题视野㊂当建筑师沉迷于在建筑单体中构建复杂性,他们不只是在浪费宝贵的资源,也是对基本建筑价值的践踏:用喧嚣㊁自负的几何杂耍替代严肃的人类空间生产实践,其深层则是陷入混乱的哲学意识和社会责任感的沦丧㊂复杂性科学或许可以在大规模建筑群体和城市空间组织中大展身手,但用于单体建筑却是严重的对象选择错误,复杂性建筑的逻辑与现实困境的根源正在于此㊂5㊀结束语复杂性建筑与复杂性科学的结盟是建筑学科学化的又一次努力㊂复杂性建筑派试图将建筑形式的发生更多建立在科学逻辑之上,降低人的干预,减少价值判断的影响,提高建筑创作的客观性㊂这种尝试推进了设计方法的进步,对当下的建筑设计产生了深刻影响㊂但作为社会产物,人为㊁为人是建筑的根基,建筑的人文属性是内在的,必须永远接受价值的约束㊂建筑学的意义在于寻求 好的空间 ,这本身就是一个典型的价值问题㊂所以建筑创作无法摆脱价值判断,建筑也从来不是理想的自然科学应用领域㊂无视这一点,一味用科学判断挤压价值判断,并不能真正提高建筑学的科学成色或推进建筑工业化的深入,只会得到另一种创造新奇形式的手段,作为一时的流行符号而沦为商业文化的附庸㊂[20]复杂性建筑对复杂性的探索,扩展了建筑学的边界㊂但是,复杂性建筑是将过度的复杂性强加给无需过度复杂的建筑,让本应服从人和现实的建筑为复杂性科学理论服务[21]㊂复杂性建筑与复杂性科学的联盟就建立在这种头脚倒置的逻辑上,这必然导致对建筑自身规则的背离,产生内在的适用性问题:功能不佳㊁极高的实施难度㊁严重的资源浪费㊁空间设置不合理和缺乏效率㊂但现实并不会迁就理论,所以复杂性建筑的营建总是与数不尽的技术妥协相伴,最终变得不够 复杂性 或局限于表皮的复杂性,其与复杂性科学的联盟也随之摇摇欲坠㊂参考文献[1]㊀博奥席耶W,斯通诺霍O.勒㊃柯布西耶全集:第1卷[M].牛燕芳,程超,译.北京:中国建筑工业出版社,2005:18.[2]㊀黄欣荣.复杂性科学与哲学[M].北京:中央编译出版社,2007.[3]㊀JENCKS C.The architecture of the jumping universe[M].Lanham:National Book Network,Inc,1996.[4]㊀JENCKS C.The new moderns[M].New York:RizzoliInternational Publications Inc,1990.[5]㊀曾欢.西方科学主义思潮的历史轨迹:以科学统一为研究视角[M].北京:世界知识出版社,2009.[6]㊀周官武,姜玉艳.查尔斯㊃詹克斯的宇源建筑理论评析[J].新建筑,2003(6):58-61.[7]㊀THOMAS.The walt disney concert hall[EB/OL].2012-09-02[2021-03-27]./building/read/35/The-Walt-Disney-Concert-Hall/1192.[8]㊀徐卫国.褶子思想,游牧空间:关于非线性建筑参数化设计的访谈[J].世界建筑,2009(8):16-17.[9]㊀LECOMTE J.Speculative architectures[EB/OL].2013-10-02[2021-03-27].https:///editorial/articles/speculative-architectures.[10]KLEIN L.Tasting space[EB/OL].2013-04-10[2021-03-29]./tasting-space.[11]CORRADI M.Coop himmelb(L)AU:paneum-wunderkammer des Brotes,Asten[EB/OL].2018-07-02[2021-03-27]./paneum-wunderkammer-des-brotes-by-coop-himmelblau.htm.(下转第7页)脆弱的联盟 周官武51㊀充薄膜均可降低钢管应变水平,提高钢管对混凝土的约束作用㊂4)钢管径厚比越大,屈服强度越高,钢管的横向变形系数越大㊂钢管与混凝土间填充薄膜的试件横向系数大于钢管与混凝土间涂油处理的试件㊂5)基于Mander模型建议了钢管约束陶粒混凝土短柱轴压极限承载力计算公式,计算结果与试验结果吻合良好㊂参考文献[1]㊀中华人民共和国建设部.轻集料混凝土技术规程:JGJ512002[S].北京:中国建筑工业出版社,2002.[2]㊀YU Q L,SPIESZ P,BROUWERS H.Ultralightweight concrete:conceptual design and performance evaluation[J].Cement& Concrete Composites,2015,61:18-28.[3]㊀刘平,葛婷,王小亮.LC7.5轻质陶粒混凝土的配制与性能研究[J].建材发展导向,2019,17(12):105-108.[4]㊀GAO J,SUN W,MORINO K.Mechanical properties of steelfiber-reinforced,high-strength,lightweight concrete[J].Cement and Concrete Composites,1997,19(4):307-313. 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写一篇逻辑与悖论的英语作文The Intriguing World of Logic and Paradoxes.In the vast landscape of human thought and understanding, logic and paradoxes stand as unique and fascinating features. Logic, the science of valid reasoning, underpins our understanding of the world, allowing us to make sense of complex ideas and arguments. Paradoxes, onthe other hand, are statements or situations that seem to contradict themselves, yet retain a profound truth that challenges our conventional wisdom.The beauty of logic lies in its precision and clarity. Logical arguments are constructed using premises that are either true or false, and through the application of deductive reasoning, conclusions are drawn that are inevitable and undeniable. This process allows us to build knowledge systems that are robust and reliable, enabling us to understand and predict the behavior of the world around us.Paradoxes, by contrast, shatter the neat lines of logic, presenting situations that seem to defy reason. They often arise in areas such as physics, mathematics, and philosophy, where the limits of our understanding are pushed to the extreme. For example, the famous "Russell's Paradox" challenges the foundation of set theory by posing the question: "What is the set of all sets that do not contain themselves?" This statement appears to be self-referential, leading to a logical contradiction that highlights thelimits of our ability to define and categorize the universe.Paradoxes, however, are not merely puzzles or contradictions in terms. They often serve as powerful tools for deepening our understanding of complex concepts. By examining paradoxes, we are forced to reevaluate our assumptions and challenge the boundaries of our knowledge. This process can lead to profound insights and new perspectives that expand our understanding of the world.The intersection of logic and paradoxes is particularly fascinating. While logic seems to provide the foundationfor all understanding, paradoxes highlight the limits of logic itself. This tension between order and chaos, between precision and ambiguity, is what makes the study of logic and paradoxes so compelling.In conclusion, the world of logic and paradoxes is a rich and complex landscape that challenges our understanding and pushes the boundaries of our knowledge. Logic provides us with the tools for clear and precise thinking, while paradoxes force us to question our assumptions and reevaluate our understanding. This tension between order and chaos, precision and ambiguity, is what makes the study of logic and paradoxes so fascinating and enduring. As we continue to explore this intriguing world, we gain a deeper understanding of the universe and our place within it.。
抽象类英语作文Ah, the abstract class – a fascinating concept in the realm of object-oriented programming, existing not as a tangible entity, but as a blueprint, a skeletal framework upon which concrete, functional classes can be built. It's like the architect's initial sketch of a grand building, capturing the essence and structure, leaving the details and embellishments to the actual construction. Much like a philosopher pondering the concept of 'chairness' rather than a specific chair, the abstract class delves into the core of 'what it means to be' a certain type of object, defining the shared characteristics and behaviors that its descendants must embody. Imagine a world of shapes – squares, circles, triangles, each with their own unique properties, yet all sharing the fundamental essence of being a shape. An abstract class, in this scenario, would be the embodiment of 'shapeness', outlining the commonalities, such as having an area and a perimeter, but leaving the specifics of calculating those values to the individual shape classes. It dictates that each shape must know how to calculate its area and perimeter, but it doesn't impose a rigid formula, allowing for flexibility and specialization. The beauty of the abstract class lies in its ability to foster code reuse and organization. Instead of rewriting the same fundamental properties and methods for each shape class, we simply inherit them from the abstract 'Shape' class, ensuring consistency and reducing redundancy.It's like having a master recipe for a cake – the abstract class – and then allowing different bakers to add their own unique flavors and decorations – the concrete classes – while still maintaining the essential cake-ness. But the abstract class isn't just about convenience; it's also about establishing contracts and ensuring correctness. By defining abstract methods, it sets expectations for its subclasses, forcing them to provide implementations for those methods. This prevents the creation of incomplete or nonsensical objects. For example, our 'Shape' class might declare an abstract method called 'draw', ensuring that every shape knows how to represent itself visually. A circle would draw itself as a round figure, a square as four straight lines, but the act of drawing itself is mandatory, enforced by the abstract class. However, the abstract class, with all its wisdom and guidance, has limitations. It cannot beinstantiated directly; it's a concept, not a concrete reality. It's like trying to build a house using only the architect's sketch – you need bricks, wood, and concrete to make it tangible. Similarly, you need to create concrete classes that inherit from the abstract class, providing the specific implementations andfilling in the missing details. The abstract class is a powerful tool in the hands of a skilled programmer, enabling the creation of elegant, well-organized, and robust code. It's the embodiment of abstraction, focusing on the 'what' rather than the 'how', providing a framework for creating families of related objects while ensuring consistency and correctness. It's a testament to the power of thinking in abstractions, of recognizing commonalities and building upon them, a cornerstone of object-oriented programming and a testament to the elegance and efficiency that can be achieved through thoughtful design.。
抽象主义和写实主义英语作文Abstractionism and RealismThe debate between abstractionism and realism has been a longstanding one in the world of art. Both movements have their own unique approaches, philosophies, and legacies, which have shaped the artistic landscape over the centuries. In this essay, we will explore the defining characteristics of these two artistic styles, their historical context, and the ongoing dialogue between them.Abstractionism, as the name suggests, is a style of art that moves away from the realistic representation of the natural world. Instead, abstract artists seek to convey emotions, ideas, and concepts through the use of color, shape, line, and texture. Rather than depicting the physical world, they aim to create a visual language that speaks to the viewer's senses and emotions. Pioneers of the abstract movement, such as Wassily Kandinsky, Piet Mondrian, and Jackson Pollock, believed that art should not be constrained by the limitations of realism, but should instead explore the boundless possibilities of the imagination.One of the key principles of abstractionism is the rejection oftraditional representational techniques. Abstract artists often abandon the use of perspective, proportion, and realistic depiction in favor of a more intuitive and expressive approach. They may use bold, vibrant colors, geometric shapes, or gestural brushstrokes to create a sense of movement, rhythm, and emotion. The goal is not to create a faithful representation of reality, but to evoke a emotional response in the viewer.The rise of abstractionism can be traced back to the early 20th century, when artists began to question the traditional conventions of art. The Cubist movement, led by Pablo Picasso and Georges Braque, was a precursor to the abstract style, as it fragmented and distorted the representation of reality. This paved the way for the emergence of pure abstraction, which sought to move beyond the constraints of the physical world and explore the realm of the mind and spirit.In contrast, realism is an artistic style that aims to depict the world as it is, without embellishment or idealization. Realist artists strive to capture the details, textures, and nuances of the natural world, often using meticulous techniques to achieve a high level of accuracy and detail. The goal of realism is to create a faithful representation of reality, to the point where the viewer can almost believe that they are looking at a photograph rather than a painting.The origins of realism can be traced back to the 19th century, when artists such as Gustave Courbet, Jean-François Millet, and Honoré Daumier sought to challenge the dominant Romantic and Academic styles of the time. These artists believed that art should reflect the everyday lives and experiences of the common people, rather than the idealized and heroic subjects that were typical of the Romantic movement.One of the key characteristics of realism is the use of naturalistic techniques, such as accurate rendering of light and shadow, attention to detail, and a focus on the mundane and ordinary. Realist artists often used photographic references to achieve a high level of accuracy, and they were known for their meticulous attention to detail. This approach was in stark contrast to the more expressive and subjective styles of Romanticism and Impressionism.While abstractionism and realism may seem like polar opposites, they are both valid and important artistic movements that have contributed to the richness and diversity of the art world. In fact, there have been many artists who have straddled the line between these two styles, combining elements of both in their work.One such artist is Andrew Wyeth, who is known for his realistic depictions of the natural world, but with a subtle and poetic quality that hints at the abstract. His paintings, such as "Christina's World"and "Snow Storm," capture the beauty and complexity of the natural world, but with a dreamlike and introspective quality that invites the viewer to engage with the work on a deeper level.Another artist who has explored the intersection of abstractionism and realism is David Hockney, who is known for his vibrant and colorful paintings that blend realistic and abstract elements. His works often feature realistic depictions of the natural world, but with a bold and expressive use of color and composition that gives them a distinctly abstract quality.In the contemporary art world, the dialogue between abstractionism and realism continues to evolve. Some artists have embraced a hybrid approach, blending elements of both styles in their work, while others have remained firmly committed to one or the other. Regardless of their approach, the ongoing debate between these two artistic movements continues to inspire and challenge artists and viewers alike.In conclusion, the debate between abstractionism and realism is a complex and multifaceted one that has shaped the art world for centuries. While these two styles may seem like opposites, they are both valid and important artistic movements that have contributed to the richness and diversity of the art world. Whether one prefers the expressive and emotive qualities of abstractionism or themeticulous and realistic depictions of realism, there is no denying the enduring appeal and significance of these two artistic traditions.。
Using Temporal Logic to SpecifyAdaptive Program Semantics∗Ji Zhang and Betty H.C.ChengSoftware Engineering and Network Systems LaboratoryDepartment of Computer Science and EngineeringMichigan State UniversityEast Lansing,Michigan48824tted:{zh1IntroductionIncreasingly,computer software must adapt to changing conditions in both the supporting computing and communication infrastructure,as well as in the surrounding physical environment(1).However,adaptive programs may be prone to errant behavior due to its innate high complexity and possibly im-precise requirements.The benefit expected from adaptations,such as higher reliability and higher availability,may be countered by the errors introduced during the adaptive software development process.Furthermore,the correct-ness of adaptation becomes most crucial when the adaptive software is applied in a safety-critical domain,such as the control software for medical devices, etc.Correctness of adaptive programs cannot be properly addressed without precisely specifying the requirements for the adaptive programs.This paper introduces specifications for three commonly used adaptation semantics and two composition techniques to be used for constructing the temporal logic specification of an adaptive program.Numerous techniques have been proposed to address the correctness of adap-tations.Kulkarni et al.(2)introduced a transitional-invariant lattice approach that uses theorem proving techniques to show that during and after an adapta-tion,the adaptive program is always in correct states with respect to satisfying the transitional-invariants.Some approaches(3;4;5)use formal languages to describe the structural changes of the software at the design and implemen-tation levels.Other approaches(6;7;8;9;10;11;12;13)design adaptation protocols or algorithms to be used during component replacement to achieve a rigorous and safe adaptation procedure.Different approaches assume different adaptation semantics.For example,Appavoo et al.(12)introduced a hot-swapping technique,which does not allow the old and the new components to execute simultaneously to achieve strict sequential semantics.In contrast,in order to improve performance,Chen et al.(11)proposed a graceful adaptation process,which allows the old component and the new component to overlap their executions.These different semantics are implied by their designs and implementations.All of the above techniques focus on the design and the im-plementation of achieving adaptability,while the requirements for adaptation are largely assumed or ambiguous.We believe that the semantics for adaptive software should be explicitly cap-tured at the requirements level(14).The correctness of adaptive software can then be evaluated with respect to its adaptation requirements specification.A recent survey(15)describes numerous research efforts that have proposed ways to formally specify dynamically adaptive programs in the past several years.Graph-based approaches model the dynamic architectures of adaptive programs as graph transformations(16;17;18).Architecture Description Lan-guage(ADL)-based approaches model adaptive programs with connection andreconnection of connectors(10;19;4).A few efforts have formally specified the behavioral changes of adaptive programs,including those that use process algebras to specify the behavior of adaptive programs(20;21;22).This paper focuses on the specification of requirements of adaptations with temporal logics.We model an adaptive program as the composition of afinite number of steady-state programs(20)(briefly programs)and the adaptations among these programs.We assume that the properties(e.g.liveness and safety properties)of each program have already been specified with a Linear Tempo-ral Logic(LTL)formula(23).To specify an adaptation from one program to another,we introduce the Adapt operator-extended LTL(A-LTL),an extension to LTL.We introduce three basic adaptation semantics and use A-LTL to for-mally specify their semantics.We can compose the basic adaptation semantics with two types of compositional procedures:neighborhood compositions and sequential compositions to derive more complex adaptation semantics.We introduce adaptation semantics graphs,a graph-based representation of adap-tive programs semantics,which can be automatically processed to generate adaptive program specifications.The formal specifications for adaptive programs precisely describe the objec-tives for adaptive programs,which facilitate rigorous software requirements specifications,and thus improves the assurance of the software.The adap-tation semantics graphs and the generated temporal logic specifications may serve as guidance for the adaptation developers to clarify the intent for the adaptive program.The temporal specifications also enable us to perform nu-merous automated analyses of the adaptive program,such as specification consistency,model checking to verify the correctness of a program model, dynamic insertion of adaptation logic code into the program,etc.We have successfully applied our specification technique to a number of adap-tive mobile computing applications,including MetaSockets(24).The remain-der of this paper is organized as follows.In Section2,we introduce A-LTL and describe three basic adaptation semantics.Section3describes neighborhood specification compositions,sequential specification compositions,and adapta-tion semantics graphs.Section4illustrates our approach with a MetaSockets example.Section5concludes the paper and discusses future directions.2Adaptation SemanticsIn this paper,we take a most general view of programs,i.e.,all programs and adaptive programs are considered as state machines(FSAs).An adaptive program changes its behavior during its execution.The state space describing each different kind of steady-state(20)behavior is a non-adaptive program,orbriefly a program.The state space describing the change of behavior from one program(source program)to another(target program)is a simple adaptive program,which can be identified by the source and target program pair.2.1Adapt Operator-Extended LTLLTL is a temporal extension to propositional logic(23).An LTL formula is constructed over a set of atomic propositions(Π),using¬(not)and∧(and) boolean operators,and (next)and U(until)temporal connectives.Other operators are defined as abbreviations over the above basic operators,such as ∨(or),→(imply),↔(co-imply),♦(eventually),2(always),etc.Existing LTL operators are insufficient for specifying adaptation behavior. In LTL,the operator closest to capturing the meaning of adaptation is the until(U)operator.However,we cannot express an adaptation from the be-havior specified withφto the behavior specified withψusingφUψfor the following reason:If a state sequenceσ=s0,s1,···satisfiesφUψ(denoted as σ|=φUψ),thenφshould hold for all suffixes ofσstarting from all the states before a certain state.However,adaptation semantics usually only requireφto hold for a given interval ofσ.Several temporal logics,including the choppy logic(25),the Propositional Interval Temporal Logic(PITL)(26;27;28;29;30),and the Interval Temporal Logic(ITL)(31),are capable of expressing adaptation behavior.However,these logics are both too complex and incon-venient for our adaptation specification purposes.By“inconvenient”we mean that they do not have direct notation support.To specify adaptation behavior,we extend LTL with the adapt operator (“Ω ”).Informally,a program satisfies“φΩ ψ”(φ,ψ,andΩare three tem-poral logic formulae)means that the program initially satisfiesφ.In a certain state A,it stops being constrained byφ,and in the next state B,it starts to satisfyψ.We formally define A-LTL as follows:•Ifφis an LTL formula,thenφis also an A-LTL formula.•Ifφandψare both A-LTL formulae,thenξ=φΩ ψis an A-LTL formula.•Ifφandψare both A-LTL formulae,then¬φ,φ∧ψ,φ∨ψ,andφUψare all A-LTL formulae.We define the A-LTL semantics as follows.•Ifσis an infinite state sequence andφis an LTL formula,thenσsatisfies φin A-LTL if and only ifσsatisfiesφin LTL.Formally,σ|=φiffσ|=φin LTL.•Ifσis afinite state sequence andφis an A-LTL formula,thenσ|=fφiffσ |=φ,whereσ is an infinite state sequence constructed by repeating thelast state ofσ.•σ|=φΩ ψiffthere exist afinite state sequenceσ =(s0,s1,···s k)and an infinite state sequenceσ =(s k+1,s k+2,···),such thatσ=σ σ ,σ |=fφ,σ |=ψ,and(s k,s k+1)|=fΩ,whereφ,ψ,andΩare A-LTL formulae.A sequence satisfyingφΩ ψcan be considered the concatenation of two subsequences,where thefirst subsequence satisfiesφ,the second subse-quence satisfiesψ,and the two states connecting the two subsequences satisfyΩ.•Other operators(→,∧,∨,U,¬,etc)are defined similarly as those used in LTL.TheΩnotation of an adapt operator can be used for specifying additional safe conditions for the state in which the adaptation occurs and logical connections between the behavior before and after adaptation.Although in some cases, the extra constraints are not used(where we simply setΩto be true),we find this notation to be useful in many other cases.For example,we can useΩ=buffer-empty to constrain that the buffer must be empty when the adaptation occurs.We separate the behavior of an adaptive program into adaptation invariants, the properties that hold continuously during an execution of the program,and adaptation variants,the properties that change during the program’s execu-tion.Wefirst introduce three adaptation semantics specifications in A-LTL. These semantics are used to specify the adaptation variants of adaptations from a given source program to a given target program.Then we introduce composition techniques to handle general adaptive programs.Finally,we com-pose adaptation invariants with adaptation variants to specify the overall adaptive program behavior.2.2Semantics for Adaptation VariantsSeveral questions have to be answered before designing an adaptive program: (1)What is the expected behavior after adaptation?(2)What constraints,if any,exist for adaptations to occur?(3)Are the source program behavior and the target program behavior allowed to overlap?(4)Should the source/target program behavior be restricted during an adaptation,and what are the re-strictions,if any?An adaptation specification should precisely address all of the above questions.Based on results presented in the literature and our own experience,we summarize three commonly used semantics for adaptation.By formally specifying these semantics,we are able to precisely answer the above questions.We assume the source program and the target program have both been spec-ified in LTL,named base specifications.We specify the adaptation from the source program to the target program with A-LTL by extending the base specifications of the source and the target programs.For some adaptations, the source/target program behavior may need to be constrained during the adaptation.These constraints,termed restriction conditions,are specified in LTL.We assume the adaptive program has moderate computational reflection(32) capability,i.e.,it is conscious about its adaptation and the currently running steady-state program.This capability can be achieved by simply introducing flag propositions in the program to identify its current steady-state program or adaptation status.We assume that a decision-making procedure that trans-lates environment changes into specific adaptation requests is available.Our specification technique describes the expected program behavior in response to these requests.We use an atomic proposition A REQ to indicate the receipt of an adaptation request to a target program from the decision making procedure. In this section,we summarize three commonly occurring basic adaptation se-mantics interpretations from the literature(12;11;6;8)specified in terms of A-LTL.There are potentially many other possible adaptation semantics. In all three adaptation specification semantics,we denote the source and the target program base specifications as S SPEC and T SPEC,respectively.If appli-cable,the restriction condition during adaptation is R COND.We assume the flag propositions are already parts of the specifications.We use the term safe states to indicate the states where all the obligations of the source program are fulfilled,thus making it safe to terminate the source behavior.2.2.1One-point adaptation.Under one-point adaptation semantics,after receiving an adaptation requestA REQ,the program adapts to the target program T SPEC at a certain pointduring its execution.The prerequisite for one-point adaptation is that the source program S SPEC should always eventually reach a safe state during its execution.(S SPEC∧♦A REQ)Ω T SPEC(1) The formula states that the program initially satisfies S SPEC.After receiving an adaptation request,A REQ,it waits until the program reaches a safe state, i.e.,all obligations generated by S SPEC are satisfied.Then the program stops being obligated to satisfy S SPEC and starts to satisfy T SPEC.This semantics isvisually presented in Figure1(a),where circles represent a sequence of states. Solid lines represent state intervals and the label of each solid line represents the property that is held by the interval.The arrow points to the states when an adaptation request is received.This semantics is straightforward and is ex-plicitly or implicitly applied by many approaches(e.g.,(12;11;6))to deal with simple cases that do not require restraining the source behavior or overlapping the source and the target behavior.2.2.2Guided adaptation.Under guided adaptation semantics(visually depicted in Figure1(b)),after receiving an adaptation request,the programfirst restrains its source pro-gram behavior by a restriction condition,R COND,and then adapts to the target program when it reaches a safe state.This semantics is suitable for adapta-tions whose source programs do not guarantee reaching a safe state within a given amount of time.The restriction condition should ensure that the source program willfinally reach a safe state.S SPEC∧(♦A REQΩ1 R COND) Ω2 T SPEC(2) This formula states that initially S SPEC is satisfied.After an adaptation re-quest,A REQ,is received,the program should satisfy a restriction conditionRCOND(marked withΩ1 ).When the program reaches a safe state of the source,the program stops being constrained by S SPEC,and starts to satisfy T SPEC (marked withΩ2 ).The hot-swapping technique introduced by Appavoo et al(12)and the safe adaptation protocol(6)introduced in our previous work use the guided adaptation semantics.2.2.3Overlap adaptation.Under overlap adaptation semantics(visually depicted in Figure1(c)),the tar-get program behavior starts before the source program behavior stops.During the overlap of the source and the target behavior,a restriction condition is applied to safeguard the correct behavior of the program.This adaptation se-mantics is appropriate for the case when continuous service from the adaptive program is required.The restriction condition should ensure that the source program reaches a safe state.S SPEC∧(♦A REQΩ1 R COND) Ω2 true ∧ ♦A REQΩ1 T SPEC∧(R CONDΩ2 true) (3)This formula states that initially S SPEC is satisfied.After an adaptation re-quest,A REQ ,is received,the program should start to satisfy T SPEC and alsosatisfy a restriction condition,R COND (marked with Ω1 ).When the programreaches a safe state of the source program,the program stops being obliged by S SPEC and R COND (marked with Ω2 ).The graceful adaptation protocol in-troduced by Chen et al (11)and the distributed reset protocol introduced by Kulkarni et al (8)use the overlap adaptationsemantics.SPEC S SPECTSPEC S SPECT REQRSPEC S SPECTREQCONDFig.1.Adaptation semantics2.2.4Safety and Liveness Properties.Temporal logics are often applied to the specifications of safety and liveness properties of a program.A safety property asserts something bad never hap-pens,while a liveness property asserts something good will eventually hap-pen (33).Although general forms of safety and liveness properties are not preserved by the adaptation semantics defined above,some common forms of safety and liveness properties are preserved.We define a formula to be a point safety property if and only if =2¬η(read as ηnever holds during execution),where ηis a point formula (a formula that does not contain temporal operators).We define a formula to be pointliveness property if and only if =2(α→♦β)(read as it is always the case that ifαholds at some point,thenβwill eventually hold at a point after that point),where bothαandβare point formulae.LEMMA1:All three adaptation semantics preserve point safety properties.That is,if (S SPEC∨T SPEC)→2¬η,whereηis a point property,thenξ→2¬η,whereξis the adaptation specification based on either semantics.We only provide the proof for the one-point adaptation case.Other cases can be proved similarly.ProofLet the adaptation specificationξbe(Formula1)ξ=(S∧♦A REQ)Ω T SPECSPECFor an arbitrary sequenceσ|=ξ,∃σ |=S SPEC∧♦A REQ andσ |=T SPEC, andσ=σ σ .Since(S SPEC∨T SPEC)→2¬η,σ |=2¬η,andσ |=2¬η. Therefore,σ|=2¬η.This lemma implies that if a propositional invariant(such as a variable is never greater than a given value)should be held in both the source and the target subprograms,then the invariant is also held by a simple adaptive program under all three adaptation semantics.This conclusion does not apply to general temporal properties.LEMMA2:Point liveness properties are preserved by all three adaptation semantics. That is,if(S SPEC∨T SPEC)→2(α→♦β),thenξ→2(α→♦β),whereξis the adaptation specification based on either semantics.Also,we only provide the proof for the one-point adaptation case.Other cases can be proved similarly.Proof:Let the adaptation specificationξbe(Formula1)∧♦A REQ)Ω T SPECξ=(SSPECFor an arbitrary sequence s0,s1,···|=ξ,∃i,such that s0,s1,···s i|=S SPEC∧♦A REQ and s i+1,s i+2,···|=T SPEC.Since(S SPEC∨T SPEC)→2(α→♦β),we have s0,s1,···s i|=2(α→♦β),and s i+1,s i+2,···|=2(α→♦β).For an arbitrary state s j,if s j|=α,then we have•if j≤i,then there exists k(j<k≤i)such that s k|=β;•if j>i,then there exists k(j<k)such that s k|=β.That is,s0,s1,···|=2(α→♦β)Therefore,we haveξ→2(α→♦β).3Specification CompositionsThus far,we have described how to specify simple adaptive programs.These specifications can be composed to describe multiple adaptation options from a single steady-state program.We can also link a sequence of adaptation spec-ifications together to describe the behavior of executions with multiple adap-tation occurrences.3.1Neighborhood CompositionA simple adaptive program starts from one program and may adapt to only one target program.A more complex adaptive program may adapt to different target programs in response to different adaptation requests.The neighborhood composition is proposed to specify multiple adaptation options from a single program.We define the neighborhood adaptive program of a program S to be the composition of all the simple adaptive programs that share the same source program S.An execution starting from S can either adapt to a target program if a corresponding adaptation request is received,or remain in S if no adaptation request is received.Assume for all target programs,the properties of the simple adaptive program from S to the i th target program T i is specified with an A-LTL formula STi SPEC,and the properties of S are specified withS SPEC.We can construct the specification for the neighborhood of S by thedisjunction of S SPEC and STi SPEC.Let N SPEC be the neighborhood specification of S,we haveN SPEC=ki=1STiSPEC∨S SPEC(4)where k is the number of simple adaptive programs sharing the same source program S.3.2Sequential CompositionA complex adaptive program may sequentially perform adaptations more than once during a single execution.For example,an adaptive program may startfrom a program A,then sequentially perform adaptations from A to B to obtain program B,and B to C to obtain program C.Assume the properties ofA,B,and C are specified with ASPEC,B SPEC,and C SPEC,respectively.The A toB adaptation specification under a given adaptation semantics is a function ofASPEC and B SPEC:AB SPEC=ADAPT1(A SPEC,B SPEC).The B to C adaptationspecification under a given adaptation semantics is a function of B SPEC andC SPEC:BC SPEC=ADAPT2(B SPEC,C SPEC).The specification of A to B to Cmay be constructed by substituting AB SPEC for the B SPEC in BC SPEC.ABCSPEC=ADAPT2(ADAPT1(A SPEC,B SPEC),C SPEC)(5)Similarly,afinite number of simple adaptive program specifications can be sequentially composed to construct the specification of more complex adaptive programs.THEOREM:Both point safety and point liveness properties are preserved by the adap-tation semantics and the two types of compositions.Proof outline:This theorem can be proved by applying Lemma1and Lemma2.•For neighborhood compositions,from the lemmas,we know that if all base specifications imply a point safety(liveness)propertyφ,then all the disjuncts implyφas well.Then the disjunction(the neighborhood composition)also impliesφ.•For sequential composition,we can prove the conclusion inductively.(1)The base case states0-step sequential composition preserves pointsafety and liveness properties.This has been proved by Lemma1and Lemma2.(2)Then we assume any n-step sequential composition preserves pointsafety and liveness properties.An n+1-step sequential composition can be considered as an n-stepsequential composition composed with a base specification.Then wecan apply Lemma1and Lemma2to the n-step adaptation compo-sition case and claim that all n+1-step sequential compositions alsopreserve point safety and liveness properties.3.3Adaptation InvariantsIn spite of adaptations of a program,some properties should be held true throughout its execution.This type of properties,such as safety and liveness properties,are adaptation invariants.We use LTL formulae to specify adap-tation invariants of the program to ensure the properties that should be held throughout the execution of an adaptive program.3.4Adaptation Specification Visualization and Automatic GenerationAn adaptive program can be visually represented as a graph,where programs are vertices and adaptations are arcs.We add temporal logic information to the graph so that we are able to derive the adaptation temporal logic specification automatically from the graph.We define an adaptation semantics graph to be a tuple(S,S0,A,P,Φ,Ψ,INV),where S is a set of vertices representing the set of programs in an adaptive program.S0⊆S is a set of initial vertices,repre-senting the initial programs of the adaptive program.FunctionΦ:S→LTL maps each program to the base specification for the program.A⊆S×S is a set of arcs representing adaptations.Function P:A→semantics name maps an adaptation to one of the semantics names{one-point,guided,overlap}.Ψ:A→LTL is a partial function that maps guided or overlap adaptation to their associated restriction conditions.INV is the set of adaptation invariants. The adaptation specifications can be derived from the adaptation semantics graph.We have implemented a prototype,ASpecGen,which uses simple edge traversal to automate this process.The complexity of the algorithm is linear to the number of adaptations.4Case StudyIn this section we use MetaSockets(24)as an illustrative example to demon-strate our adaptation specification approach.MetaSockets are constructed from the regular Java Socket and MulticastSocket classes;however,their inter-nal structure and behavior can be modified at run time in response to external conditions.MetaSocket behavior can be adapted through the insertion and removal offilters that manipulate the data stream.For example,filters can perform encryption,decryption,forward error correction,compression,and so forth.We consider a sender’s MetaSocket with three differentfilters:a data com-pressionfilter(COM),a DES64-bit encryptionfilter(DES64),and a DES 128-bit encryptionfilter(DES128).The available adaptations are data com-pressionfilter insertion and removal,and DESfilter replacement.Note that to enforce security,the DESfilters can only be replaced by other DESfilters, but cannot be removed.Thesefilters can be combined in four different config-urations:DES64,DES128,DES64with COM(DES64COM),and DES128with COM(DES128COM).We consider the MetaSocket under each configuration a program.The adaptive program is initially running in the DES64program.4.1MetaSocket SpecificationsThe specifications of the programs are described as follows:•DES64program:DES64SPEC =(2DES64FL)∧2(DES64Input(x)→♦DES64Output(x))The DES64Input(DES64Output)are events indicating the input(output) of a packet to(from)the MetaSocket under DES64configuration.1The flag proposition DES64FLindicates that the program is running under the DES64configuration.The formula states that under this configuration,for every input packet to be encoded by the DES64filter,the MetaSocket should eventually output a DES64encoded packet.The following program aspects can be interpreted in a similar way.•DES128program:DES128SPEC=(2DES128FL)∧(2(DES128Input(x)→♦DES128Output(x)))•DES64COM program:DES64COMSPEC=(2DES64COMFL)∧(2(DES64COMInput(x)→♦DES64COMOutput(x)))•DES128COM program:=DES128COMSPEC(2DES128COM FL)∧(2(DES128COMInput(x)→♦DES128COMOutput(x)))To determine the semantics of each adaptation,we consider the following factors:(1)The MetaSocket component is designed for the transmission of real-time video and audio data.Therefore,we should minimize data blocking.(2)We should not allow both the source and the target programs to input simultaneously because that will cause ambiguity in the input.(3)We should not allow the target program to output data before any output is produced from the source program,otherwise,it will complicate the logic on the receiver. Based on the above considerations,it is appropriate to apply the overlap semantics with conditions prohibiting the types of overlap discussed above.2.The adaptation semantics graph is visually presented in FigureFig.2.Visual representation of MetaSocket adaptation semantics graphWe use the DES64to DES128adaptation as an example to demonstrate the simple adaptive program specification construction.In order to use overlap semantics,we have to define restriction conditions to prevent overlap of the source and target programs input and the overlap of the source and target programs output.Therefore,we define the restriction conditions to beR(DES64-DES128)=2(¬DES64Input(x)∧¬DES128Output(x)).(6) CONDThe intuition for this restriction condition is that it should not accept any more DES64inputs and will not produce any DES128outputs until all DES64out-puts have been produced.Given the source and target program specifications, the overlap semantics,and the restriction condition,we apply Formula3toderive the following specification:DES64-DES128SPEC =(7)DES64SPEC∧ ♦A REQ(DES128)true R COND(DES64-DES128) true true ∧ A REQ(DES128)true DES128SPEC∧(R COND(DES64-DES128)true true) Formula(7)states that after the program receives an adaptation request to the DES128program(A REQ(DES128)),it should adapt to the DES128program. Furthermore,the behavior of DES64and DES128may overlap,and during the overlapping period,the program should satisfy the restriction conditionR COND(DES64-DES128).In this example,theΩnotation of the adaptationoperators are not used.We simply assign true toΩin the four adapt operator locations.With the same approach,we specify other simple adaptive programs in the adaptive program.Further,both the source and the target specifications are point liveness properties.We can unify them with the following formula by disregarding the type of inputs and outputs.2(Input(x)→♦Output(x))(8) According to Lemma2,we can conclude that the adaptation also satisfies the point liveness property.In addition to the specification for adaptation behavior,the program should also satisfy a set of adaptation invariants to maintain its integrity.•Security invariant:During program execution,the sender MetaSocket should not cause any loss of packets,i.e.,all input packets should be output:INV2=2(Input(x)→♦Output(x))Note,this invariant is already guaranteed by the point liveness preservation property of the adaptation semantics.(Formula8.)。
