Lecture 6_Requirements Engineering

Safety critical system requires a very structured development process The system with rapidly changing requirements, a less formal, flexible process is useful.

Waterfall Model

Separate and distinct phases of specification and development Specification and development are interleaved The system is developed as a series of versions (increments), with each version adding functionality to the previous version.

Throw-away prototyping

Benefits of Incremental Development



Cost related with accommodating customer requirements is minimized. Early customer feedback Customer feedback helps in identifying the problems earlier. More rapid delivery and deployment of useful software to the customer is possible, even if all the functionality has not been included.

1 Preparing for listening
to a lecture
Unit 3 Listening to Lectures
1 Preparing for listening to a lecture
Tips before listening to a lecture:
1) Find out the topic of the lecture to be delivered.
Unit 3 Listening to Lectures
2 Paying attention to the introduction
Read the following introductions of two lectures and guess the topic and content of each of them.
2 What is the relationship between carbon dioxide, greenhouse gases and the thinning ozone layer with global warming? Carbon dioxide is a greenhouse gas. Burning oil, coal and fossil fuels leads to a sharp increase in the greenhouse gas which build up and condense, forming a thick gas layer of carbon dioxide. This gas traps heat from the sun and destroys the ozone layer, the layer which protects the Earth from harmful radiation, causing global warming.

II. Observational Studies Case-control study Cross-sectional study Cohort study Case series Case report
Types of Designs (continued)
III. Other Study Types Meta analyses Experimental study Review Historical manuscript
Types of Study Variables
Continuous variables -- can be measured as precisely as instrumentation permits ➢cholesterol, HDL-cholesterol, age, per-patient change in percent diameter stenosis
Designing a Clinical Research Study
A. Stating Objective: Framing Research Question B. Defining the Study Population C. Selecting the Appropriate Study Design D. Defining the Study Variables E. Rewrite Objectives into Testable Hypotheses F. Selecting the Study Sample and Sample Size Considerations G. Bias and Masking in Clinical Studies H. Determination of Analytic Plan

To characterize fully the data needs of the prospective database users. method: questionaire, chatting, Result: requirements of database users
Database Design phases---step2
The needs of the users play a central role in the design process.
We focus on the design of the database schema in this chapter.
Database Design phases---step1
Chooses a data model and translate those requirements into a conceptual schema. method: E-R model or E-R diagram Result: E-R diagram
Database Design phases---step3
E-R model consists of:
Entity sets Relationship sets Attributes constraints

Entity sets
A database can be modeled as: a collection of entities, relationship among entities.
Incompleteness, eg:
student(student_id, select_course, grade) What happened when you insert a student who didn’t