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Lexikon

functional database

A href="module.php?name=Lexikon&file=search&eid=1&query=database">database which uses a {functional language} as its {query language}. Databases would seem to be an inappropriate application for functional languages since, a href="module.php?name=Lexikon&file=search&eid=1&query=purely functional language">purely functional language would have to return a new copy of the entire database every time (part of) it was updated. To be practically href="module.php?name=Lexikon&file=search&eid=1&query=scalable">scalable, the update mechanism must clearly be href="module.php?name=Lexikon&file=search&eid=1&query=destructive">destructive rather than functional however it is quite feasible for the {query language} to be purely functional so long as the database is considered as an argument. One approach to the update problem would use a href="module.php?name=Lexikon&file=search&eid=1&query=monad">monad to encapsulate database access and ensure it was {single threaded}. Alternative approaches have been suggested by Trinder, who suggests non-destructive updating with shared data structures, and Sutton who uses a variant of a Phil Wadler' s href="module.php?name=Lexikon&file=search&eid=1&query=linear type">linear type system. There are two main classes of functional database languages. The first is based upon href="module.php?name=Lexikon&file=search&eid=1&query=Backus">Backus' href="module.php?name=Lexikon&file=search&eid=1&query=FP">FP language, of which href="module.php?name=Lexikon&file=search&eid=1&query=FQL">FQL is probably the best known example. href="module.php?name=Lexikon&file=search&eid=1&query=Adaplan">Adaplan is a more recent language which falls into this category. More recently, people have been working on languages which are syntactically very similar to modern {functional programming language}s, but which also provide all of the features of a database language, e.g. bulk data structures which can be incrementally updated, type systems which can be incrementally updated, and all data persisting in a database. Examples are href="module.php?name=Lexikon&file=search&eid=1&query=PFL">PFL [Poulovassilis&Small, VLDB-91], and href="module.php?name=Lexikon&file=search&eid=1&query=Machiavelli">Machiavelli [Ohori et al, ACM SIGMOD Conference, 1998]. href="module.php?name=Lexikon&file=search&eid=1&query=Query optimisation">Query optimisation is very important for database languages in general and the href="module.php?name=Lexikon&file=search&eid=1&query=referential transparency">referential transparency of functional languages allows optimisations which would be harder to verify in presence of href="module.php?name=Lexikon&file=search&eid=1&query=side-effect">side-effects. [Trinder, P., "Referentially transparent database languages", 1989 Glasgow Workshop on Functional programming] [Breazu-Tannen et al., DBPL-91]. [Poulovassilis, VLDB-94]. (1995-05-09)

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Free On-line Dictionary of Computing

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