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On the Representation of Roles in ObjectOriented and Conceptual Modelling
, 2000
"... The duality of objects and relationships is so deeply embedded in our thinking that almost all modelling languages include it as a fundamental distinction. Yet there is evidence that the two are naturally complemented by a third, equally fundamental notion: that of roles. Although definitions of the ..."
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Cited by 132 (9 self)
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The duality of objects and relationships is so deeply embedded in our thinking that almost all modelling languages include it as a fundamental distinction. Yet there is evidence that the two are naturally complemented by a third, equally fundamental notion: that of roles. Although definitions of the role concept abound in the literature, we maintain that only few are truly original, and that even fewer acknowledge the intrinsic role of roles as intermediaries between relationships and the objects that engage in them. After discussing the major families of role conceptualizations, we present our own basic definition and demonstrate how it naturally accounts for many modelling issues, including multiple and dynamic classification, object collaboration, polymorphism, and substitutability. <3 2000 Elsevier Science B.V. All rights reserved.
Practical Unificationbased Parsing of Natural Language
, 1993
"... The thesis describes novel techniques and algorithms for the practical parsing of realistic Natural Language (NL) texts with a widecoverage unificationbased grammar of English. The thesis tackles two of the major problems in this area: firstly, the fact that parsing realistic inputs with such gr ..."
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Cited by 48 (7 self)
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The thesis describes novel techniques and algorithms for the practical parsing of realistic Natural Language (NL) texts with a widecoverage unificationbased grammar of English. The thesis tackles two of the major problems in this area: firstly, the fact that parsing realistic inputs with such grammars can be computationally very expensive, and secondly, the observation that many analyses are often assigned to an input, only one of which usually forms the basis of the correct interpretation. The thesis starts by presenting a new unification algorithm, justifies why it is wellsuited to practical NL parsing, and describes a bottomup active chart parser which employs this unification algorithm together with several other novel processing and optimisation techniques. Empirical results demonstrate that an implementation of this parser has significantly better practical
FiniteTree Analysis for Constraint LogicBased Languages: The Complete Unabridged Version
, 2001
"... Logic languages based on the theory of rational, possibly infinite, trees have much appeal in that rational trees allow for faster unification (due to the safe omission of the occurscheck) and increased expressivity (cyclic terms can provide very efficient representations of grammars and other usef ..."
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Cited by 40 (16 self)
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Logic languages based on the theory of rational, possibly infinite, trees have much appeal in that rational trees allow for faster unification (due to the safe omission of the occurscheck) and increased expressivity (cyclic terms can provide very efficient representations of grammars and other useful objects). Unfortunately, the use of infinite rational trees has problems. For instance, many of the builtin and library predicates are illdefined for such trees and need to be supplemented by runtime checks whose cost may be significant. Moreover, some widelyused program analysis and manipulation techniques are correct only for those parts of programs working over finite trees. It is thus important to obtain, automatically, a knowledge of the program variables (the finite variables) that, at the program points of interest, will always be bound to finite terms. For these reasons, we propose here a new dataflow analysis, based on abstract interpretation, that captures such information. We present a parametric domain where a simple component for recording finite variables is coupled, in the style of the open product construction of Cortesi et al., with a generic domain (the parameter of the construction) providing sharing information. The sharing domain is abstractly specified so as to guarantee the correctness of the combined domain and the generality of the approach. This finitetree analysis domain is further enhanced by coupling it with a domain of Boolean functions, called finitetree dependencies, that precisely captures how the finiteness of some variables influences the finiteness of other variables. We also summarize our experimental results showing how finitetree analysis, enhanced with finitetree dependencies, is a practical means of obtaining precise finitenes...
A Complete And Recursive Feature Theory
, 1992
"... Various feature descriptions are being employed in logic programming languages and constrainedbased grammar formalisms. The common notational primitive of these descriptions are functional attributes called features. The descriptions considered in this paper are the possibly quantified firstorder ..."
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Cited by 27 (5 self)
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Various feature descriptions are being employed in logic programming languages and constrainedbased grammar formalisms. The common notational primitive of these descriptions are functional attributes called features. The descriptions considered in this paper are the possibly quantified firstorder formulae obtained from a signature of binary and unary predicates called features and sorts, respectively. We establish a firstorder theory FT by means of three axiom schemes, show its completeness, and construct three elementarily equivalent models. One of the models consists of socalled feature graphs, a data structure common in computational linguistics. The other two models consist of socalled feature trees, a recordlike data structure generalizing the trees corresponding to firstorder terms. Our completeness proof exhibits a terminating simplification system deciding validity and satisfiability of possibly quantified feature descriptions.
The FirstOrder Theory of Ordering Constraints over Feature Trees
 Discrete Mathematics and Theoretical Computer Science
, 2001
"... The system FT of ordering constraints over feature trees has been introduced as an extension of the system FT of equality constraints over feature trees. We investigate the firstorder theory of FT and its fragments, both over finite trees and over possibly infinite trees. We prove that the firstor ..."
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Cited by 19 (5 self)
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The system FT of ordering constraints over feature trees has been introduced as an extension of the system FT of equality constraints over feature trees. We investigate the firstorder theory of FT and its fragments, both over finite trees and over possibly infinite trees. We prove that the firstorder theory of FT is undecidable, in contrast to the firstorder theory of FT which is wellknown to be decidable. We determine the complexity of the entailment problem of FT with existential quantification to be PSPACEcomplete, by proving its equivalence to the inclusion problem of nondeterministic finite automata. Our reduction from the entailment problem to the inclusion problem is based on a new alogrithm that, given an existential formula of FT , computes a finite automaton which accepts all its logic consequences.
A settheoretical approach for the induction of inheritance hierarchies
 Electronic Notes in Theoretical Computer Science
, 2001
"... An approach for the automatic construction of inheritance hierarchies is presented. It is based on the strict settheoretical point of view in the mathematical theory of Formal Concept Analysis. The resulting hierarchies are concept lattices. An extension of the approach to the induction of nonmonot ..."
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Cited by 15 (4 self)
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An approach for the automatic construction of inheritance hierarchies is presented. It is based on the strict settheoretical point of view in the mathematical theory of Formal Concept Analysis. The resulting hierarchies are concept lattices. An extension of the approach to the induction of nonmonotonic inheritance networks is also discussed. It turns out that the main ideas of Formal Concept Analysis, i. e. the formal context, the concept lattice and the set of implications, provide three different ways of looking at the data to be represented, each of which provides a different way to solve problems of knowledge representation. 1
Ordering Constraints over Feature Trees
, 1999
"... Feature trees are the formal basis for algorithms manipulating record like structures in constraint programming, computational linguistics and in concrete applications like software configuration management. Feature trees model records, and constraints over feature trees yield extensible and modular ..."
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Cited by 14 (5 self)
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Feature trees are the formal basis for algorithms manipulating record like structures in constraint programming, computational linguistics and in concrete applications like software configuration management. Feature trees model records, and constraints over feature trees yield extensible and modular record descriptions. We introduce the constraint system FT of ordering constraints interpreted over feature trees. Under the view that feature trees represent symbolic information, the relation corresponds to the information ordering ("carries less information than"). We present two algorithms in cubic time, one for the satisfiability problem and one for the entailment problem of FT . We show that FT has the independence property. We are thus able to handle negative conjuncts via entailment and obtain a cubic algorithm that decides the satisfiability of conjunctions of positive and negated ordering constraints over feature trees. Furthermore, we reduce the satisfiability problem of Dorre's weak subsumption constraints to the satisfiability problem of FT and improve the complexity bound for solving weak subsumption constraints from O(n^5) to O(n³).
Classification in Featurebased Default Inheritance Hierarchies
, 1993
"... Abstract. Increasingly, inheritance hierarchies are being used to reduce redundancy in natural language processing lexicons. Systems that utilize inheritance hierarchies need to be able to insert words under the optimal set of classes in these hierarchies. In this paper, we formalize this problem fo ..."
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Cited by 14 (0 self)
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Abstract. Increasingly, inheritance hierarchies are being used to reduce redundancy in natural language processing lexicons. Systems that utilize inheritance hierarchies need to be able to insert words under the optimal set of classes in these hierarchies. In this paper, we formalize this problem for featurebased default inheritance hierarchies. Since the problem turns out to be NPcomplete, we present an approximation algorithm for it. We show that this algorithm is efficient and that it performs well with respect to a number of standard problems for default inheritance. A prototype implementation has been tested on lexical hierarchies and it has produced encouraging results. The work presented here is also relevant to other types of default hierarchies. Abstract. In zunehmendem Masse werden Erbschaftshierarchien zur kompakten Beschreibung von Worteigenschaften in Sprachverarbeitungslexica verwendet. Systeme, die Erbschaftshierarchien benützen, müssen Worte in die optimale Klasse (oder Menge von Klassen) der Hierarchien einfügen können. Dieser Beitrag formalisiert das Problem für merkmalsbasierte defaultHierarchien. Da das Problem NPvollständig ist, wird hier ein Approximationsalgorithmus vorgeschlagen. Es wird gezeigt, daß der Algorithmus effizient ist und daß er in Hinsicht auf einige Standardprobleme der defaultHierarchien gut funktioniert. Eine Prototypimplementierung zeigt gute Resultate an einigen Hierarchien, die für Lexica der Computerlinguistik geschrieben wurden. Diese Forschung kann auch für andere Arten von defaultHierarchien angewendet werden. 1
Towards a Semantics for Lexical Rules as used in HPSG
 In Proceedings of the ACQUILEX II Workshop on the Formalisation and Use of Lexical Rules
, 1995
"... We show how a mechanism that captures the functionality of lexical rules can be integrated into the logical setup for hpsg provided by King (1989, 1994) without having to enlarge the logic with a metalevel or extra notions such as defaults. A notation for lexical rules is introduced and a rewrite sy ..."
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Cited by 13 (3 self)
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We show how a mechanism that captures the functionality of lexical rules can be integrated into the logical setup for hpsg provided by King (1989, 1994) without having to enlarge the logic with a metalevel or extra notions such as defaults. A notation for lexical rules is introduced and a rewrite system is defined to map the lexical rules as specified by the linguist into ordinary constraints in the King logic. We therefore show how a denotational semantics for lexical rules as used in hpsg linguistics can be provided. Keywords: lexical rules, hpsg, logical issues of the hpsg architecture. 1 Introduction Lexical rules have been used by linguists to express generalizations over the lexicon for over 25 years. In the paradigm of hpsg they have become one of the key mechanisms used in current analysis, be it for crossserial dependencies and preposition stranding in Dutch, clitic climbing in French and Italian, verbsecond, finitivization and partial constituent fronting in German, or pa...