Semantic entity detection from multiple ASR hypotheses within the WFST framework

The paper presents a novel approach to named entity detection from ASR lattices. Since the described method not only detects the named entities but also assigns a detailed semantic interpretation to them, we call our approach the semantic entity detection. All the algorithms are designed to use automata operations defined within the framework of weighted finite state transducers (WFST) - the ASR lattices are nowadays frequently represented as weighted acceptors. The expert knowledge about the semantics of the task at hand can be first expressed in the form of a context free grammar and then converted to the FST form. We use a WFST optimization to obtain compact representation of the ASR lattice. The WFST framework also allows to use the word confusion networks as another representation of multiple ASR hypotheses. That way we can use the full power of composition and optimization operations implemented in the OpenFST toolkit for our semantic entity detection algorithm. The devised method also employs the concept of a factor automaton; this approach allows us to overcome the need for a filler model and consequently makes the method more general. The paper includes experimental evaluation of the proposed algorithm and compares the performance obtained by using the one-best word hypothesis, optimized lattices and word confusion networks.