from
The Free On-line Dictionary of Computing (8 July 2008)
functional database
<database, language> A {database} which uses a {functional
language} as its {query language}.
Databases would seem to be an inappropriate application for
functional languages since, a {purely functional language}
would have to return a new copy of the entire database every
time (part of) it was updated. To be practically {scalable},
the update mechanism must clearly be {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 {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 {linear type} system.
There are two main classes of functional database languages.
The first is based upon {Backus}' {FP} language, of which
{FQL} is probably the best known example. {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
languages}, 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
{PFL} [Poulovassilis&Small, VLDB-91], and {Machiavelli} [Ohori
et al, ACM SIGMOD Conference, 1998].
{Query optimisation} is very important for database languages
in general and the {referential transparency} of functional
languages allows optimisations which would be harder to verify
in presence of {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)