GCSE Computing/Databases

What you need to know

1. How does a DBMS allow separation of data from applications?

A DBMS can present users (and other application programs) with views of the data that are particular to the needs of the application. The views are largely independent of the way that the data is physically stored in the database files. Application programs that need to use the data do not have to include code to directly access the database. Instead, the programs send requests and instructions to the database via the DBMS.

2. Why is it desirable to separate data from applications?

A prime advantage of modern databases is that the database and applications that use the data can be altered independently of each other. Without a DBMS, applications were data dependent. This means that the way in which the data was organised and the way in which it was accessed were both decided by the requirements of the application that accessed it. An understanding of how the data was stored and how it needed to be accessed had to be coded into the application.

3. What are the advantages of applications being data independant?

4. What are the principal features of a DBMS?

The prime purpose of a relational database management system is to maintain data integrity. This means all the rules and relationships between data are consistent at all times. But a good DBMS will have other features as well. These include: .A command language that allows you to create, delete and alter the database (data description language or DDL) .A way of documenting all the internal structures that make up the database (data dictionary) .A language to support the manipulation and processing of the data (data manipulation language). .Support the ability to view the database from different viewpoints according to the requirements of the user .Provide some level of security and access control to the data

The database concept

• (a) Describe a database as a persistent organised store of data
• (b) Explain the use of data handling software to create, maintain and interrogate a database.

The DBMS

• (c) describe how a DBMS allows the separation of data from applications and why this is desirable
• (d) describe the principal features of a DBMS and how they can be used to create customised data handling applications.

Relational databases

• (e) understand the relationship between entities and tables
• (f) understand the components of a relational database, such as tables, forms, queries, reports and modules
• (g) understand the use of logical operators in framing database queries
• (h) explain the use of key fields to connect tables and avoid data redundancy
• (i) describe methods of validating data as it is input.