Extending a description logic to cope with the completeness of multimedia documents

Logic is a suit able tool for modetling the retrieval of multirnedia docurnents, as it offers a well founded and universally accepted framework for representing documents and user requests. while viewiug retrieval as inference. Especially the lat ter feature is of extrerne int.erest to inforrnation retrieval. as it allows, among other t hings. to make proper usage of the many kinds of knowledge involved in this rask. However,logic as it is also suffers from severa! drawbacks t hat make it too rigid to cope with real dornains. We address one of these problems, by defining a logic for the retrieval of multimedia documents allowing the expression and proper handling of closure assertions. A closure assertion is meta-knowledge about the completeness of the knowledge on a specified individu al or predicate symbol.