Modernizing IBM eServer iSeries Application Data Access - A Roadmap Cornerstone

12 Modernizing IBM Eserver iSeries Application Data Acess - A Roadmap Cornerstone

2.1 Background

To start with, let us take a very short look at the history and the components of SQL.

2.1.1 A short look at the history of SQL

In 1970, Dr. E.F. Codd, an employee of IBM, presented a relational model for databases. His

ideas were the groundwork for all modern Relational Database Management Systems

(RDBMS). The Structured English Query Language (SEQUEL) was developed in 1974 by

D.D. Chamberlin, an employee at IBM’s lab in San Jose (California) and renamed Structured

Query Language (SQL) three years later. The first commercial database with relational

capabilities was introduced with IBMs System/38, the predecessor of the AS/400 and iSeries.

The language SQL is not proprietary. This, and the fact that both the American National

Standards Institute (ANSI) and the International Standards Organization (ISO) formed SQL

Standards committees in 1986 and 1987, were major reasons for SQL to become a widely

accepted standard that is implemented in almost all RDBMSs.

At this time, three standards have been published by the ANSI-SQL group:

򐂰 SQL89 (SQL1)

򐂰 SQL92 (SQL2)

򐂰 SQL99 (SQL3)

2.1.2 The main parts of SQL

SQL includes a Data Definition Language (DDL) and a Data Manipulation Language (DML).

DDL contains statements to create, modify, and drop table and index definitions, as well as to

grant and revoke authorities on these objects. DML contains statements to insert, retrieve,

update, and delete database content.

For more information on SQL, you may refer to the following publications:

http://publib.boulder.ibm.com/pubs/html/as400/infocenter.html

This is the iSeries Information Center Entry Page, where you can find a lot of iSeries-related

information.

2.2 Reasons to modernize

In this section we take a more detailed look at the key points enumerated in the introduction

of this chapter.

2.2.1 Standard compliancy

In the introduction above, we learned that SQL is a widely used standard. But what does that

mean to your business? Possibly a lot:

򐂰 It is fairly easy to find books, training classes, and other resources on SQL in case you

need some advice or want to improve your knowledge of SQL.

򐂰 Most software tools support SQL, but the same is not true for DDS.

򐂰 You gain in portability. Your database definition and part of your business rules (defined

using Referential Integrity; see 2.2.6, “Data integrity” on page 17, for more details) can be

extracted easily and ported onto another platform or another DBMS, if that is required.