1. A computer-implemented method of registering an ontology with a search engine provider, comprising: receiving an ontology definition comprising a plurality of terms from an ontology owner; and creating an ontology index based on the ontology definition and a keyword index, wherein the keyword index includes a plurality of relationships between a plurality of keywords and a plurality of documents residing on a network, and wherein the ontology index includes a plurality of relationships between the plurality of terms and the plurality of documents residing on the network, comprising: creating a plurality of ontology index entries, wherein each of the plurality of ontology index entries corresponds to a respective one of the plurality of terms in the ontology definition; and for each of the plurality of ontology index entries: searching the keyword index for the corresponding one of the plurality of terms to identify one or more related documents; and inserting an identifier of the identified one or more related documents into the ontology index entry.