In order to execute database queries efficiently, they are usually translated into an algebra: a small set of operations together with some equivalences. The operations are implemented very efficiently by the database engine, and the equivalences are used to optimise the query. Since query languages for object-oriented databases are more complex than their relational counterparts, the algebra and translation, or processing framework, is more elaborate.
OBJECT-ORIENTED DATABASE QUERY LANGUAGE QUERY OPTIMISATION COLLECTION TYPE COMPREHENSIONS