Sublanguage
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In relational database theory, the term sublanguage, coined by E. F. Codd in 1970, refers to a computer language used to define or manipulate the structure and contents of a relational database management system (RDBMS). Typical sublanguages associated with modern RDBMS's are QBE (Query by Example) and SQL (Structured Query Language). In 1985, Codd encapsulated his thinking in twelve rules which every database must satisfy in order to be truly relational. The fifth rule is known as the Comprehensive data sublanguage rule, and states:
- A relational system may support several languages and various modes of terminal use (for example, the fill-in-the-blanks mode). However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings, and that is comprehensive in supporting all of the following items:
- Data definition
- View definition
- Data manipulation (interactive and by program)
- Integrity constraints
- Authorization
- Transaction boundaries (begin, commit, and rollback)
The term sublanguage has also sometimes been used to denote a computer language that is a subset of another language. For instance, ALGOL 68S was a subset of ALGOL 68 designed to make it possible to write a single-pass compiler for this sublanguage. In [Informatics], natural language processing, and [machine translation], a sublanguage is the language of a restricted domain, particularly a technical domain. In mathematical terms, "a subset of the sentences of a language forms a sublanguage of that language if it is closed under some operations of the language: e.g., if when two members of a subset are operated on, as by and or because, the resultant is also a member of that subset" (Z.S. Harris Language and Information, Columbia U. Press, 1988, p. 34).
[edit] References
- Codd, E. (1985). "Is Your DBMS Really Relational?" and "Does Your DBMS Run By the Rules?" ComputerWorld, October 14 and October 21.
- Sager, N. Nhàn, N.T. (2002) The computability of strings, transformations, and sublanguage, in The Legacy of Zellig Harris, eds. by Bruce E. Nevin and Stephen M. Johnson. John Benjamins Publishing Co., Amsterdam/Philadelphia. Volume 2, Chapter 4, pp. 79-120.
