An approach to abductive inference developed in the TAC-ITUS project has resulted in a dramatic simplification of how the problem of interpreting texts is conceptualized. Its use in solving the local pragmatics problems of reference, compound nominals, syntactic ambiguity, and metonymy is described and illustrated. It also suggests an elegant and thorough integration of syntax, semantics, and pragmatics.
FASTUS is a system for extracting information from free text in English, and potentially other languages as well, for entry into a database, and potentially for other applications. It works essentially as a cascaded, nondeterministic finite state automaton. There are four steps in the operation of FASTUS. In Step 1 sentences are scanned for certain trigger words to determine whether further processing should be done. In Step 2 noun groups, verb groups, and prepositions and some other particles are recognized. The input to Step 3 is the sequence of phrases recognized in Step 2; patterns of interest are identified in Step 3 and corresponding "incident structures" are built up. In Step 4 incident structures that derive from the same incident are identified and merged, and these are used in generating database entries. FASTUS is an order of magnitude faster than any comparable system; it can process a news report in an average of less than eleven seconds. This translates directly into fast development time. In the three and a half weeks between its first use and the MUC-4 evaluation in May 1992, we were able to build up its domain knowledge to a point where it was among the leaders in the evaluation.
This book is an investigation into the problems of generating natural language utterances to satisfy specific goals the speaker has in mind. It is thus an ambitious and significant contribution to research on language generation in artificial intelligence, which has previously concentrated in the main on the problem of translation from an internal semantic representation into the target language. Dr. Appelt's approach, based on a possible-worlds semantics of an intensional logic of knowledge and action, enables him to develop a formal representation of the effects of illocutionary acts and the speaker's beliefs about the hearer's knowledge of the world. The theory is embodied and illustrated in a computer system, KAMP (Knowledge and Modalities Planner), described in the book.
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