The article presents the experience of developing computer ontology as one of the tools for automatic natural language processing. A computer ontology that contains a consistent specification of meanings of lexical units with different relations between them represents a model of lexical semantics and both syntactic and semantic valencies, reflecting the Tibetan linguistic picture of the world. The article describes the approach of using computer ontology as a means of introducing semantic restrictions for morphosyntactic disambiguation on the basis of the corpus of indigenous grammatical treatises.