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Relational model General information
34 U929-J-Z125-9-76
SQL - a uniform language for relational database systems
Development of the theory of relational databases by Codd and others was paralleled by
work on the user interface for such systems. The initial results of this work were first
presented in the “System R” prototype and were continually revised and supplemented with
further results in the years following. The first commercial implementations of this language
interface have been on the market since the early eighties under the name of SQL.
Major standardization organizations such as ANSI and ISO have been working on
standardizing SQL since 1982.
With the active support of Siemens, the ISO standard for SQL (ISO 9075:1989(E)) was
established in 1987.
The power of the SQL-DML enables users to perform all of the essential operations on the
database. New data can be inserted in the tables or data already in the tables can be
queried, updated or deleted. Tables can be linked with one another, and the result sets of
two or more queries combined. All processing by the DML is set-oriented. For example, a
selection yields a table which the user can then process further record by record, and an
update statement changes all the records that satisfy the specified conditions. It is precisely
this set-oriented processing that distinguishes SQL from database languages for non-
relational database systems.
This is also a major advantage for users in that it enables them to have a variety of actions
performed on the database by issuing a single statement. In the case of record-oriented
processing, all of these actions would have to be initiated separately.
In summary, SQL has the following main features:
– SQL is based on the relational data model developed by E.F. Codd and incorporates all
of its advantages: powerful data manipulation by means of descriptive set-processing
statements and simple data organization, which does not affect programs when altered.
– The use of the standardized SQL interface promotes the portability of DB applications
and provides a high degree of independence from special database interfaces (facili-
tates the procurement of know-how).
– SQL is a uniform, easy-to-learn language.
Each of these features results in increased productivity in application programming and
improves the cost-effectiveness of database use overall. The obvious advantages of SQL
have prompted nearly all manufacturers to offer the SQL interface in their present products
or to announce its incorporation in their future ones.
A separate manual (see the “SQL for UDS/SQL” manual) provides detailed information on
the basic concepts and terminology of SQL and describes the SQL language set supported
by UDS/SQL.