An ontology that is used to determine relationships between instances of objects having types. The ontology is made from a text file containing a DAML+OIL description of the ontology and includes a set of ontology objects and an accelerator that accelerates determination of the relationships. The accelerator is implemented using database tables and indexes. The ontology may be used as a data filter. A decision-centered visualization system uses the ontology to relate data items contained in event instances to task instances and to determine for a given task instance what portion of the data in the data item should be provided for display by a given task instance.