Object query language
OQL was developed to play the role of SQL for Object-Oriented Databases, especially those adhering to the ODMG Standard  where the language is defined. Unlike SQL, OQL is a functional language, and its operators can be composed to an arbitrary level of nesting within a query provided the query remains type-correct. Fegaras and Maier  have shown how OQL expressions have a direct translation into monoid Comprehensions.
Optimisation techniques for OQL that exploit its inherent functional nature are discussed in [5, 6, 8]. OQL has been influential in the development of the SQL3 standard and also the functional core of the XQuery language for XML. Thus optimisation techniques developed for OQL are also applicable to these languages.
The fundamental modelling concept of object identifiersfor entity instances was accepted into the database mainstream in the late 1980s, and the move to using SQL-like syntax for querying such data...
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