SPECIAL IMPLEMENTATION CONSIDERATIONS - Database Design and Development: An Essential Guide for IT Professionals - page 387

SQL 3 Draft

ANSI X3.135

ANSI X3.135

ANSI X3.135

Initial Level

1986
1989
1992

Figure 13-8 SQL: evolution of standards.

Evolution of Standards Both the American National Standards Institute (ANSI)
and the International Standards Organization (ISO) have adopted and standard-
ized SQL over the years. Figure 13-8 shows the evolution of SQL as standardiza-
tion continues. Note how each new level adds and consolidates features.

Highlights of Each Version

ANSI X3.135—1986
Definition of language constructs: verbs, clauses, operators, syntax
Details of functions left to the discretion of implementers
ANSI X3.135—1989
Integrity enhancement
Support for primary and foreign key
ANSI X3.135—1992 (SQL 2)
Language enhancements
Detailed definitions for existing functions
SQL 3 Draft
Object-oriented capabilities

Data Definition in SQL

When you design a database system, you proceed through the logical and physical
phases. The components developed in these phases form the basis for your data-
base system. For the database management system (DBMS) to manage the data-
base content, the components of the logical design and the physical design must be
defined to the DBMS. In a relational database system, you have to define the logical
structures in terms of tables, columns, and primary keys. You need to relate the
tables and rows to physical files, blocks, and records. These also must be defined to
the DBMS.
Data definition language serves to define the logical and physical components
to the DBMS. You know that the definitions are recorded in the data dictionary of
the DBMS. The data definition language component of SQL makes it possible to
define the logical and physical components of the relational data model to the
DBMS.