The original concept behind relational databases was first published by Edgar Frank Codd (an IBM researcher,
commonly referred to as E.F.Codd) in a paper, “Derivability, Redundancy, and Consistency of Relations Stored in
Large Data Banks” (RJ599), dated 08/19/1969. However, what is commonly viewed as the first milestone in the
development of relational databases is a publication by Codd entitled „A Relational Model of Data for Large Shared Data Banks“ in Communications of the ACM (Vol.
13, No. 6, June 1970, pp. 377-87). This was only a revised version of the 1969 paper.
This article awoke massive public opinion in both the academic community and industry in the feasibility and
usability of relational databases for commercial products.
Several other articles by Codd throughout the seventies and eighties are still viewed almost as gospel for
relational database implementation. One of these articles is the famous so-called 12 rules for relational
databases, which was publish in two parts in Computerworld. Part 1 was named „Is Your DBMS Really Relational?"
(published 10/14/1985); Part 2 was called „Does Your DBMS Run By the Rules?" (10/21/1985).
Codd continuously added new rules to these 12 originals and published them in his book "The Relational Model for
Database Management, Version 2" (Addison-Wesley, 1990).
But to continue with the evolution of SQL and relational databases we must take a step back in time to the year
In 1974 Donald Chamberlin and others developed for IBM System R as a first prototype of a relational database.
The Query Language was named SEQUEL (Structured English Query Language).
System R also became part of IBM’s prototype SEQUEL-XRM during 1974 and 1975. It was completely rewritten in
1976 – 1977. In addition there were new features like multi-table and multi-user capabilities implemented. The
result of this revision was quickly named SEQUEL/2, but had to be renamed due to legal reasons to SQL because
Hawker Siddeley Aircraft Company claimed the trademark SEQUEL for themselves.
In 1978 systematic tests were performed to prove real world usability on customers’ systems. It became a big
success for IBM, because this new system proved both useful and practical. With this result, IBM began to develop
commercial products based on System R. SQL/DS came out in 1981; DB2 hit the streets in 1983.
But although IBM had done most of the research work, in fact, it was a small unknown software company named
Relational Software to first release a RDBMS in 1979, two years before IBM. This unknown software company was
later renamed Oracle. As an interesting sidenote, Relational Software released its product as Version 2. Obviously
a brilliant marketing move: no one had to worry about a buggy and/or unstable Version 1 of this new kind of
The victory of SQL was well on its way.
Being the de facto standard, SQL became also an official standard through the American National Standards
Institute (ANSI) certification in 1986 (X3.135-1986). But this standard could only be viewed as a cleaned-up
version of DB2’s SQL dialect. Just one year later, in 1987, followed the standardization by the International
Standards Organization (ISO 9075-1987).
Only two years later, ANSI released a revised standard (X3.135-1989). So did ISO with ISO/IEC 9075:1989.
Partially due to the commercial interests of the software firms, many parts of the standard were left vague
and unclear. This standard was viewed as the least common denominator and missed its intention. It was some 150
To strengthen and establish the standard, ANSI revised SQL89 thoroughly, and released in 1992 the SQL2 standard
(X3.135-1992). This time they did it right!
Several weaknesses of SQL89 were eliminated. Further conceptual features were standardized although at that
time they were far beyond the possibilities of all relational databases. The new standard was some 500 pages long.
But even today there is no single product available that fully complies with SQL92. Due to this disparity there
were three level of conformity introduced:
- Entry level conformance. Only small changes compared
- Intermediate conformance. At least 50% of the standard
has to be implemented.
- Full conformance.
Recently SQL99, also known as SQL3, was published. This standard addresses some of the modern, previously
ignored features of certain modern SQL systems. There are object-relational database models, call-level interfaces
and integrity management.
SQL99 replaces SQL92 level of conformance with its own: Core SQL99 and Enhanced SQL99.
SQL99 is split into 5 parts:
- Framework (SQL / Framework)
- Foundation (SQL / Foundation)
- Call Level Interface (SQL / CLI)
- Persistent Stored Modules (SQL / PSM)
- Host Languages Binding (SQL / Bindings)
Another impressive feature of SQL99 is the number of pages of this standard, some 2,000 pages long.
SQL has established itself as standard of database query language.
So what’s next?
Well, at a minimum SQL4 is due to be released in this century.