1. An ontology processing system that performs predetermined processing using an ontology that systematically expresses domain knowledge representing concepts and relationships between concepts, the ontology processing system comprising: a dimension-classified ontology storage unit that stores at least one dimension-classified ontology, for each of dimensions for combinations of conditions, the dimension-classified ontologies differing in domain knowledge content; a basic ontology storage unit that stores a basic ontology including domain knowledge content for when there is no condition; a dimension priority storage unit that stores dimension priorities representing priorities of the respective dimensions; a dimension-classified ontology fetcher that, when a condition is specified, fetches from the dimension-classified ontology storage unit one or more dimension-classified ontologies that meet the specified condition; a multidimensional ontology generator that overwrites the content of the fetched dimension-classified ontologies onto the basic ontology according to the dimension priorities of the dimension priority storage unit, in order from the dimension-classified ontology with the lowest dimension priority, and generates a multidimensional ontology to be used with the specified condition; and a processer that performs predetermined processing using the multidimensional ontology generated by the multidimensional ontology generator.