Ontologies are emerging as a key solution to knowledge sharing, semantic retrieval, information exchange among heterogeneous systems, etc. An ontology management system (OMS), which supports building, using and maintaining of ontologies, and which provides a mechanism for querying ontologies and an easy-to-use programming interface to interact with them and their instances, is consequently witnessing in the areas. To promote research and development of OMS, this paper defines its general framework and functional modules according to that of a database management system (DBMS). And it analyzes each OMS sub-module in details while considering integrity of the whole system. An OMS is a powerful tool to create ontologies and expand the application, scope and quality of existing ones.