The metalevel concepts for an object-oriented database model are presented. Usually, systems that include a metaclass concept are either only implicitly supporting the management of meta information, which restricts the application of this concept, or explicitly giving unrestricted access to manipulate metaclasses, which results in inconsistent states of the system. To make the explicit support more system-controlled, the metascheme is partitioned into two parts: the system view and the application view. Possible scheme level operations, the representation of methods and their implementation as a special kind of meta information, and a simple extension to the query algebra of the underlying object-oriented database system that allow users to query objects and metaobjects within a single algebra expression are described.
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