Unification of disjunctive

Xem 1-12 trên 12 kết quả Unification of disjunctive
  • The paper describes a new implementation of feature structures containing disjunctive values, which can be characterized by the following main points: Local representation of embedded disjunctions, avoidance of expansion to disjunctive normal form and of repeated test-unifications for checking consistence. The method is based on a modification of Kasper and Rounds' calculus of feature descriptions and its correctness therefore is easy to see. It can handle cyclic structures and has been incorporated successfully into an environment for grammar development. ...

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  • This paper proposes a method for packing feature structures, which automatically collapses equivalent parts of lexical/phrasal feature structures of HPSG into a single packed feature structure. This method avoids redundant repetition of unification of those parts. Preliminary experiments show that this method can significantly improve a unification speed in parsing.

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  • Unification of disjunctive feature descriptions is important for efficient unification-based parsing. This paper presents constraint projection, a new method for unification of disjunctive feature structures represented by logical constraints. Constraint projection is a generalization of constraint unification, and is more efficient because constraint projection has a mechanism for abandoning information irrelevant to a goal specified by a list of variables. These works are based on graph unification rather than on term unification.

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  • Although disjunction has been used in several unificationbased grammar formalisms, existing methods of unification have been unsatisfactory for descriptions containing large quantities of disjunction, because they require exponential time. This paper describes a method of unification by successive approximation, resulting in better average performance.

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  • The notion of a Horn extended feature structure (HoXF) is introduced, which is a feature structure constrained so that its only allowable extensions are those satisfying some set of llorn clauses in featureterm logic, l l o X F ' s greatly generalize ordinary feature structures in admitting explicit representation of negative and implicational constraints. In contradistinction to the general case in which arbitrary logical constraints are allowed (for which the best known algorithms are exponential), there is a highly tractable algorithm for the unification of HoXF's. ...

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  • Substantial efforts have been made in order to cope with disjunctions in constraint based grammar formalisms (e.g. [Kasper, 1987; Maxwell and Kaplan, 1991; DSrre and Eisele, 1990].). This paper describes the roles of disjunctions and inheritance in the use of feature structures and their formal semantics. With the notion of contexts we abstract from the graph structure of feature structures and properly define the search space of alternatives.

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  • This paper proposes a method for generating a logicalconstraint-based internal representation from a unification grammar formalism with disjunctive information. Unification grammar formalisms based on path equations and lists of pairs of labels and values are better than those based on first-order terms in that the former is easier to describe and to understand. Parsing with term-based internal representations is more efficient than parsing with graph-based representations.

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  • A grammatical description often applies to a linguistic object only when that object has certain features. Such conditional descriptions can be indirectly modeled in Kay's Functional Unification Grammar (FUG) using functional descriptions that are embedded within disjunctive alternatives. An extension to FUG is proposed that allows for a direct representation of conditional descriptions. This extension has been used to model the input conditions on the systems of systemic grammar. Conditional descriptions are formally defined in terms of logical implication and negation.

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  • We investigate the logical structure of concepts generated by conjunction and disjunction over a monotonic multiple inheritance network where concept nodes represent linguistic categories and links indicate basic inclusion (ISA) and disjointhess (ISNOTA) relations. We model the distinction between primitive and defined concepts as well as between closed- and open-world reasoning. We apply our logical analysis to the sort inheritance and unification system of HPSG and also to classification in systemic choice systems. ...

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  • This paper presents a connectionist syntactic parser which uses Structure Unification Grammar as its grammatical framework. The parser is implemented in a connectionist architecture which stores and dynamically manipulates symbolic representations, but which can't represent arbitrary disjunction and has bounded memory. These problems can be overcome with Structure Unification Grammar's extensive use of partial descriptions.

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  • Attributes are partial: it need not be the case that every attribute is d ef!ned for every complex element. The set of attribute-value structures partially ordered by the subsumption relation (together with all additional entity T that every attribute-value structure subsumes) forms a lattice, and the join operation on this lattice is called the unification operati(m 119]. Example: (from [16]). The attribute-value structure (1) has six complex elements labelled el ... e6 and two corastant elements, singular and third. ...

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  • We propose a treatment of coordination based on the concepts of functor, argument and subcategorization. Its formalization comprises two parts which are conceptually independent. On one hand, we have extended the feature structure unification to disjunctive and set values in order to check the compatibility and the satisfiability of subcategorization requirements by structured complements.

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