Ulrich Koch (koch@mailhost.uni-koblenz.de)
Mon, 12 Dec 94 16:55:23 +0100
Hello Michal (and other HPSGers), I'm not the most knowledgeable person on this list, but I'll try my hands on this one. Somebody please correct me if I blunder. The following is based on [P&S 1994], Chapters 1-8. The SLASH feature expresses a long-distance dependency between a "missing" or "empty" constituent (the trace) and a non-empty constituent (the filler) that fills the "gap" left by the trace. A SYNSEM value X[SLASH Y] says basically, "I'm an X that still lacks a Y," or, "add a Y to me and I'll be an X." Example: What do you know _? Here the LOCAL value of "what" (the filler) is [1], and the SLASH value of "_" (the trace) is {[1]}. (SLASH is set-valued.) The trace is called the "bottom" of the SLASH dependency, i.e. where it "starts out." Nonlocal features like SLASH come in pairs: SLASH, REL and QUE each occur once in NONLOCAL|INHERITED (NONLOC|INHER) and once in NONLOCAL|TO-BIND. Nonempty TO-BIND|SLASH values occur in the Filler-Head Schema, which looks like this: X --> [LOCAL [1]], S[INHER|SLASH {[1], ...}, TO-BIND|SLASH {[1]}] FILLER-DTR HEAD-DTR This takes care of the "top" of the SLASH dependency (where it's "bound off," i.e. terminated). In between is the "middle" (where the SLASH dependency "percolates up the tree"). It's provided by the Nonlocal Feature Principle, which says: In a headed phrase, for each nonlocal feature F, the INHER|F value on the mother is the union of the INHER|F values on all daughters, minus the TO-BIND|F value on the head daughter. The tree for the above example looks roughly like this: S[INHER|SLASH {}] / \ NP[LOCAL [1]] S[INHER|SLASH {[1]} | TO-BIND|SLASH {[1]}] | / | \ | V NP VP[INHER|SLASH {[1]}] | | | / \ | | | V NP[LOCAL [1] | | | | INHER|SLASH {[1]}] | | | | | what do you know _ Here the SLASH dependency [1] "percolates up" from the trace until it's "bound off" (by the Filler-Head Schema) at the topmost S node. Chapter 9 of [P&S 1994] contains a trace-less account of filler-gap dependencies, where the nonempty INHER|SLASH value is not introduced by a trace, but by a lexical rule. Bibl.: [P&S 1994] Pollard, Carl J. and Sag, Ivan A. (1994) Head-driven phrase structure grammar. University of Chicago Press and CSLI Publications. Ulrich Koch, stud. inform. Rose tint my world Keep me safe from my trouble and pain
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