Chris Collins on Software

What is the history of Structured English Query Language and what is its relationship to SQL?

In 1970 Dr. E. F. Codd published his paper,“A Relational Model of Data for Large Shared Data Banks”. This became the foundation for the relation database system. This paper described a new way to structure data within a database, and led to the relational database systems we use today.

While Dr. Codd’s paper defined the structure, his colleagues Donald D. Chamberlin and Raymond F. Boyce at IBM had been developing a query language known as SQUARE (Specifying Queries As Relational Expressions), which used set theory and predicate mathematics to select data from the database. This language had a terse mathematical syntax, but became the proving ground for concepts which are important to database manipulation.

By 1974, Chamberlin and Boyce published “SEQUEL: A Structured English Query Language” which detailed their refinements to SQUARE and introduced us to the data retrieval aspects of SEQUEL. This new SEQUEL language was as powerful as SQUARE, but Chamberlin and Boyce “kept in mind the notions of top down structured programming, the need for linear notation, and the need for readable programs that are easy to maintain and modify”. The resulting syntax could be described as block-structured English keyword syntax.

Using SQUARE to find all the names and salaries of employees who are in the toy department and whose manager is Anderson would be represented as:

NAME, SAL EMP DEPT, MGR ('TOY', 'ANDERSON')

The equivalent query in SEQUEL would be represented as:

SELECT NAME, SAL

FROM EMP

WHERE DEPT = 'TOY'

AND MGR = 'ANDERSON'

This type of syntax had many advantages, such as being easily learned by non-experts. Both SQUARE and SEQUEL had the advantage of being declarative languages. This allowed users to specify ‘what’ to do rather than ‘how’ to do it as in imperative, or procedural languages.

SEQUEL was later renamed to SQL by dropping the vowels, because SEQUEL was a trade mark registered by the Hawker Siddeley aircraft company. Thus SQL was born.

References

D D Chamberlin, R. F. Boyce, 1974, SEQUEL: A Structured English Query Language. Retrieved on May 16, 2007 from http://www.almaden.ibm.com/cs/people/chamberlin/sequel-1974.pdf.

Wikipedia Contributors, SQL. Retrieved on May 16 from http://en.wikipedia.org/wiki/SQL.