Semantics and constraint parsing of word graphs

A constraint-based parser capable of processing a word graph containing multiple sentence hypotheses has been developed. When syntactic constraints are applied to a word graph, this parse is able to prune the graph of many ungrammatical sentence hypotheses and limit the possible parses of the remaining sentences. However, in many cases syntactic information alone is insufficient for selecting a single sentence hypothesis from a word graph. Hence, semantic constraints have been added to the parser to limit ambiguity further. The authors review the constraint parsing algorithm and then provide a simple example illustrating how syntactic and semantic features can be used to prune word candidates from a word graph and eliminate incorrect parses for the remaining sentences. They also report on the effectiveness of syntactic and semantic constraints for reducing the ambiguity of word networks constructed for N-best sentence hypotheses provided by the ATIS (Air Travel Information System) database.<>