This paper describes an ontology-based knowledge system for creating and sharing user?s personal objects, with support for querying semantic associations. The user specifies and populates a local ontology, which helps him to organize his personal objects. For users who wish to work cooperatively, or divulgate their personal objects in the so-called community of practices, the system provides a mapping between the local and global ontologies, both defined using the Resource Description Framework (RDF) model. This global ontology is available on a Web server and provides global semantic query capability. The mapping task, as well as the objects organization process, is supported by a thesaurus. It ensures that each user?s view is preserved, as he is able to visualize and query objects using his original vocabulary, independently of the way they have been represented in the global ontology.