Introduction to SQL, A Brief History.

The history of SQL begins in an IBM laboratory in San Jose, California, where SQL was developed in the late 1970's. The initials stand for Structured Query Language, and the language itself is often referred to as "sequel." It was originally developed for IBM's DB2 product (a relational database management system, or RDBMS, that can still be bought today for various platforms and environments). In fact, SQL makes an RDBMS possible. SQL is a nonprocedural language, in contrast to the procedural or third generation languages (3GLs) such as COBOL and C that had been created up to that time.
The characteristic that differentiates a DBMS from an RDBMS is that the RDBMS provides a set-oriented database language. For most RDBMSs, this set-oriented database language is SQL. Set oriented means that SQL processes sets of data in groups.
Two standards organizations, the American National Standards Institute (ANSI) andthe International Standards Organization (ISO), currently promote SQL standards toindustry. The ANSI-92 standard is the standard for the SQL used throughout this book.Although these standard-making bodies prepare standards for database system designersto follow, all database products differ from the ANSI standard to some degree. Inaddition, most systems provide some proprietary extensions to SQL that extend thelanguage into a true procedural language. We have used various RDBMSs to preparethe examples in this book to give you an idea of what to expect from the commondatabase systems. (We discuss procedural SQL--known as PL/SQL--on Day 18, "PL/SQL: AnIntroduction," and Transact-SQL on Day 19, "Transact-SQL: An Introduction.")
A little background on the evolution of databases and database theory will help you understand the workings of SQL. Database systems store information in every conceivable business environment. From large tracking databases such as airline reservation systems to a child's baseball card collection, database systems store and distribute the data that we depend on. Until the last few years, large database systems could be run only on large mainframe computers. These machines have traditionally been expensive to design, purchase, and maintain. However, today's generation of powerful, inexpensive workstation computers enables programmers to design software that maintains and distributes data quickly and inexpensively.