SPECIAL IMPLEMENTATION CONSIDERATIONS - Database Design and Development: An Essential Guide for IT Professionals - page 381

Storage
of Data

Relational Model

RELATIONS
Tuples
Attributes
Primary Keys
Foreign Keys

Data
Dictionary

DDL

Data
Files

Usage
of Data

Figure 13-2 DDL component.

Storage
of Data

Relational Model

RELATIONS
Tuples
Attributes
Primary Keys
Foreign Keys

Data
Dictionary

DDL

Data
Files

Retrieve
Data

Usage
of Data

Figure 13-3 DML component: data access.

database system. Data access provides for retrieval of relevant portions of data
based on various criteria.
Figure 13-3 indicates those features of DML that deal with data access.

Data Maintenance Data access and retrieval are just one part of data manipula-
tion. The other parts include adding new data, deleting unwanted data, and
revising data values as necessary. The data maintenance part of DML allows the
maintenance of the data in the database.
Figure 13-4 presents the features of DML that are relevant to data maintenance
in a database system.

Data Control “Usage of data in the database” implies controlled usage under
proper authorization. There must be one language component to ensure proper data
control. The data control language (DCL) enables data security and control through
methods for proper access for authorized users. Authorization must include opening