2. The ontology query system of claim 1 wherein the ontology query includes a third clause indicating at least one condition that must be satisfied by at least one of first values of properties or second values of compositions of properties defined on the at least one subject class.
1. An ontology query system comprising: a central computer within an distributed ontology system comprising a global ontology directory, the global ontology directory indexing class and relation definitions, wherein class definitions define ontological classes, the ontological classes being sets of instances having a common characterization, and relation definitions define ontological relations, the ontological relations being inter-relationships between classes that are used to relate instances of one or more classes; a plurality of ontology server computers, comprising: a corresponding plurality of repositories, each repository of the plurality of repositories containing different portions of the ontological classes and relation definitions and different portions of superclass-subclass definitions, and wherein at least one superclass-subclass definition is contained in a repository of the plurality of repositories that resides on a different ontology server computer than the ontology server computer housing the repository containing the definition of the subclass or the ontology server computer housing the repository containing the definition of the superclass; and a corresponding plurality of query processors for responding to queries relating to the ontological classes and the relation definitions in said plurality of repositories; an authoring tool communicating with said repositories for updating said repositories, comprising: a validator for ensuring that updates made to said repositories maintain backward compatibility, so that expressions that were valid before being updated remain valid after said updating is performed; and a relation editor for editing relation definitions in said repositories, by expanding domains of relations; an Extensible Markup Language (XML) embedder communicating with said repositories for embedding an XML Schema within a designated repository by identifying class and relation definitions implicit in the XML Schema, wherein said identifying comprises user-aided choosing of class and relation definitions implicit in the XML Schema that are embedded within the designated repository; a computer network connecting said central computer with said plurality of ontology server computers; and a query builder capable of generating an ontology query, the ontology query including a first clause and a second clause, wherein the first clause indicates at least one subject class to which the ontology query applies, wherein the second clause indicates at least one of a property or a composition of properties to be displayed, wherein the at least one of the property or the composition of properties is defined on the at least one subject class, and wherein the at least one subject class is in the ontological classes.