Key Terms

In data base design, we need to be familiar with several terms. Suppose we have a sales status system designed to give the sales activities of each salesperson. 

1. User's view is a profile that the user expects to see on a report. In our example, the user's view is a sales report.

2. Processing refers to the changes made produce the sales report.

3. Data model is a framework or a mental image of the user's view. The salesperson and the items sold.The steps are determined by the analyst as a framework for producing the user's view-the report.

   4. Data file is the area where the actual files are 8tored. The storage sequence is determined by the data model. In our example, the data are organized by salesperson and the Hen s under each salesperson.

          In a data base environment, the DBMS is the software that provides the interface between the data file on disk and the program that requests processing. The procedure is as follows:

  1. The user requests a sales report through the application program. The application program uses a data manipulation language (DML) to tell the DBMS what is required.

  2. The DBMS refers to the data model, which describes the view in a language called the data definition language (DDL). The DBMS uses DDL to determine how data must be structured to produce the user's view.

   3. The DBMS requests the input/output control system (IDCS) to retrieve the information from physical storage as specified by the application program. The output is the sales report.

To Summarize,

        1. DML manipulates data; it specifies what is required.

        2. DDL describes how data are structured.

        3. DBMS manages data according to DML requests and DDL descriptions.

As you can tell, DBMS performs several important functions:

   1. Storing, retrieving, and updating data.

   2. Creating program and data independence. Either one can be altered independently of the other.

   3. Enforcing procedures for data integrity. Data are immune from deliberate alteration because the programmer has no direct method of altering physical databases.

   4. Reducing data redundancy. Data are stored and maintained only once.

   5. Providing security facilities for defining users and enforcing authorizations. Access                       is limited to authorized users by passwords or similar schemes.

  6. Reducing physical storage requirements by separating the logical and physical aspects of the data base