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246 Part Two Information Technology Infrastructure

on their own. Access and availability of information will be increased and
program development and maintenance costs reduced because users and
programmers can perform ad hoc queries of data in the database. The DBMS
enables the organization to centrally manage data, their use, and security.
Relational DBMS
Contemporary DBMS use different database models to keep track of entities,
attributes, and relationships. The most popular type of DBMS today for PCs
as well as for larger computers and mainframes is the relational DBMS.
Relational databases represent data as two-dimensional tables (called relations).
Tables may be referred to as files. Each table contains data on an entity and its
attributes. Microsoft Access is a relational DBMS for desktop systems, whereas
DB2, Oracle Database, and Microsoft SQL Server are relational DBMS for large
mainframes and midrange computers. MySQL is a popular open source DBMS,
and Oracle Database Lite is a DBMS for mobile computing devices.
Let’s look at how a relational database organizes data about suppliers and
parts (see Figure 6.4). The database has a separate table for the entity SUPPLIER
and a table for the entity PART. Each table consists of a grid of columns and

FIGURE 6.4 RELATIONAL DATABASE TABLES

A relational database organizes data in the form of two-dimensional tables. Illustrated here are tables for the entities SUPPLIER and PART
showing how they represent each entity and its attributes. Supplier_Number is a primary key for the SUPPLIER table and a foreign key for
the PART table.

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