Class Algebra as a Description

A class algebra has been used to model the query and data manipulation language for a prototype object-oriented database system which is being implemented for the WorldWide Web ?]. The Prolog prototype (i.e. operational semantics, if you will) is lo-dan=prologProgs=modeloo:txt. The class algebra includes a Boolean algebra for class union, intersection, and complement (i.e. diierence with any). This Boolean algebra is extended with dot (partof), cross product, projection, and selection to make it subsume relational algebra. All classes which are deened with these class expressions have an extent which is the set of all objects that are described by the class expression. As such, this class algebra is a kind of description logic. Moreover, subclass deeni-tion, variable and function declaration, data assignment , function and relation deenition, and other side-eeect operators such as insert/delete are deened for this class algebra. A comparison is made between this class algebra and ODMG-93's OQL ?], SQL, Prolog, and rst-order predicate logic.