tailieunhanh - Báo cáo khoa học: "On Parsing Strategies and Closure"

This paper proposes a welcome hypothesis: a computationally simple device z is sufficient for processing natural language. Traditionally it has been argued that processing natural language syntax requires very powerful machinery. Many engineers have come to this rather grim conclusion; almost all working parers are actually Turing Machines (TM). | On Parsing Strategies and Closure1 Kenneth Church MIT Cambridge MA 02139 This paper proposes a welcome hypothesis a computationally simple device2 3 is sufficient for processing natural language. Traditionally it has been argued that processing natural language syntax requires very powerful machinery. Many engineers have come to this rather grim conclusion almost all working parsers are actually Turing Machines TM . For example. Woods believed that a parser should have TM complexity and specifically designed his Augmented Transition Networks ATNs to be Turing Equivalent. 1 It is. well known cf. Chomsky64 that the strict context-free grammar model is not an adequate mechanism for characterizing the subtleties of natural languages. Woods70 If the problem is really as hard as it appears then the only solution is to grin and bear it. Our own position is that parsing acceptable sentences is simpler because there are constraints on human performance that drastically reduce the computational complexity. Although Woods correctly observes that competence models are very complex this observation may not apply directly to a performance problem such as parsing The claim is that performance limitations actually reduce parsing complexity. This suggests two interesting questions a How is the performance mode constrained so as to reduce its complexity and b How can the constrained performance model naturally approximate competence idealizations 1. The FS Hypothesis We assume a severe processing limitation on available short term memory STM as commonly suggested in the psycholinguistic literature Frazier79 Frazier and Fodor79 Cowper76 Kimball73 75 . Technically a machine with limited memory is a finite state machine FSM which has very good complexity bounds compared to a TM. 1. I would like to thank Peter Szolovits Mitch Marcus Bill Martin Bob Berwick Joan Bresnan Jon Allen Ramesh Patil Bill Swartout Jay Keyser Ken Wexler Howard Lasnik Dave McDonald Per-Kristian Halvorsen and .