Introduction

One of the important issues facing commercial (and other) organizations is the issue of "managing" its data. That is, how do you ensure:

1. Availability
2. Data integrity/quality
3. Security
4. Efficient retrieval

For most organizations the answer is the effective use of appropriate "database technology". The computer-based systems that employ such technologies are referred to as "database systems". Figure 2-1 (pg 26) of the text presents the components of a typical database system. The components are:

1. Database:

   On pg 15 a definition is presented. A slightly different definition is:

   A self-describing collection of persistent, integrated data items.

   The terms self-describing, persistent and integrated may be loosely defined thus:

   • By self-describing we mean that the database contains data about itself (meta-data).
   • By persistent we mean that once data is stored in a database it can only be removed by an explicit request to the DBMS.
   • By integrated we mean that details of the relationships between entities in the database are included in the definition of the database.

2. Software

   The software consists of:

   1. Database Management System (DBMS) Engine

      The software that handles all access to the database. Conceptually, you may think of the role of the DBMS thus:

      • A user (or application program) issues a request for data.
      • The DBMS intercepts the request, analyzes it, and determines if the request can be satisfied.
      • The DBMS determines how to satisfy the request most efficiently.
      • The DBMS executes the necessary operations on the physical database and passes the result to the user.
      Note: The DBMS utilities and tools used by developers and database administrators are usually also considered part of the DBMS.

   2. Application Programs

      The applications developed in some programming language that make data requests to the DBMS.

3. Users

   Typically, by user we mean:

   • Application programmers.
   • Database Administrators (i.e. IT staff responsible for proper functioning of the database system)
   • End users (i.e. IT and non-IT staff that use the database system to perform their job function)

Benefits

Several benefits of database systems are presented on pg 14 (i.e. Integrated Data, Reduced Data Duplication, Program/Data Independence, Easier Representation of the Users Perspective). In addition, database systems are also considered to provide the following benefits:

1. Security:

   User and application security privileges are usually defined in the database. Since access to the database is mediated by the DBMS then, the DBMS also controls access to data.

2. Transaction support:

   A transaction is a logical unit of work that may involve several database operations. The typical example involves the operations necessary to transfer funds between two accounts. Clearly, at least two database operations are involved. That is, the transaction is not complete until both accounts are properly updated. DBMS provide facilities to define the operations that constitute a "logical unit of work".

Readings: Chapter 1 and Chapter 2.