Database
A database may be defined as a collection of interrelated data stored together with as little redundancy as possible to serve one or more applications in an optimal fashion; the data are stored so that they are independents of programs which use the data; a common and controlled approach is used in adding new data and in modifying and retrieving existing data within the data base one system is said to contain a collection of databases if they are entirely separate in structure.
The restructuring should be possible without having to rewrite the application program and in general should cause as little upheaval as possible the ease with which a database can be changed will have a major effect on the rate at which data-processing application can be developed in a corporation.
The term data independence is often quoted as being one of the main attributes of a database int implies that the data and the may be changed without changing the other, when a single setoff data items serves a variety of applications, different application programs perceive different relationships between the data items, to a large extent database organization is concerned with the as how and where the data are stored.
A database used for many applications can have multiple interconnection referred to as entities. An entity may be a tangible object or no tangible if it has various properties which we may wish to record. It can describe the real world. The data item represents an attribute and the attribute must be associated which the relevant entity. We relevant entity we design values to the attributes one attribute has a special significance in that it identifies the entity.
Logical data description is called a model.
We must distinguish a record and a record examples, when talking about all personnel records when it is really a record type, not combined with its data value.
A model is used to describe the database used storage in the database data item type and record types of general charts, subschema paragraph refers to an application programmer view of data, many different patterns can get from one mode. The schema
and the subschema are both used by the database management system the primary function of which is to serve the application programs by execution their data operations.
A DBMS will usually be handling multiple data calls concurrently, it must organize its system buffers so that different data operations can be in process together, it provides a data definition language to specify the conceptual schema and most likely some of the details regarding the implementation of the conceptual schema by the physical schema the describe the conceptual schema in terms for a “data model”.
The choice of a data model is a difficult one, since it must be such enough in structure to describe significant aspects of the real world, yet it must be possible to determine fairly automatically an efficient implementation of the conceptual conceptual schema by a physical schema. It should be emphasized that while a DBMS might be used to build small databases many databases involve millions of bytes and an inefficient implementation can be disastrous.
The hierarchical and network structures have been used for DBMS since the 1960’s . the relational structure was introduced in the early 1970’s.
In the relational model two-dimensional tables represent the entities and their relationships every table represents an entities are represented by common columns containing values from a domain or range of possible values .The end user is presented with a simple data model his and her request and don not reflect any complexities due to system-oriented aspects a relational data model is what the user sees , but it is mot necessarily what will be implemented physically.
The relational data model removes the details of storage structure and access strategy from the user inter-face the model providers a relatively higher degree of data to make use of this property of the relational data model however, the design of the relations must be complete and accurate. Although some DBMS based on the relational data model are commercially available today it is difficult to provide a complete set of operational capabilities with required efficiency on a large scale it appears today that technological improvements in providing faster and more reliable hardware may answer the question positively.
