O - line Parsability and the Well - foundedness of Subsumption

Typed feature structures are used extensively for the speciication of linguistic information in many formalisms. The subsumption relation orders TFSs by their information content. We prove that subsumption of acyclic TFSs is well-founded, whereas in the presence of cycles general TFS subsumption is not well-founded. We show an application of this result for parsing, where the well-foundedness of subsumption is used to guarantee termination for grammars that are oo-line parsable. We deene a new version of oo-line parsability that is less strict than the existing one; thus termination is guaranteed for parsing with a larger set of grammars. This paper has not been submitted elsewhere in identical or similar form