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Modality in Dialogue: Planning, Pragmatics and Computation
, 1998
"... Natural language generation (NLG) is first and foremost a reasoning task. In this reasoning, a system plans a communicative act that will signal key facts about the domain to the hearer. In generating action descriptions, this reasoning draws on characterizations both of the causal properties of the ..."
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Cited by 36 (9 self)
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Natural language generation (NLG) is first and foremost a reasoning task. In this reasoning, a system plans a communicative act that will signal key facts about the domain to the hearer. In generating action descriptions, this reasoning draws on characterizations both of the causal properties of the domain and the states of knowledge of the participants in the conversation. This dissertation shows how such characterizations can be specified declaratively and accessed efficiently in NLG. The heart of this dissertation is a study of logical statements about knowledge and action in modal logic. By investigating the prooftheory of modal logic from a logic programming point of view, I show how many kinds of modal statements can be seen as straightforward instructions for computationally manageable search, just as Prolog clauses can. These modal statements provide sufficient expressive resources for an NLG system to represent the effects of actions in the world or to model an addressee whose knowledge in some respects exceeds and in other respects falls short of its own. To illustrate the use of such statements, I describe how the SPUD sentence planner exploits a modal knowledge base to
Model Elimination without Contrapositives and its Application to PTTP
 PROCEEDINGS OF CADE12, SPRINGER LNAI 814
, 1994
"... We give modifications of model elimination which do not necessitate the use of contrapositives. These restart model elimination calculi are proven sound and complete and their implementation by PTTP is depicted. The corresponding proof procedures are evaluated by a number of runtime experiments and ..."
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Cited by 22 (8 self)
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We give modifications of model elimination which do not necessitate the use of contrapositives. These restart model elimination calculi are proven sound and complete and their implementation by PTTP is depicted. The corresponding proof procedures are evaluated by a number of runtime experiments and they are compared to other well known provers. Finally we relate our results to other calculi, namely the connection method, modified problem reduction format and NearHorn Prolog.
On Computing Minimal Models
 Annals of Mathematics and Artificial Intelligence
, 1993
"... This paper addresses the problem of computing the minimal models of a given CNF propositional theory. We present two groups of algorithms. Algorithms in the first group are efficient when the theory is almost Horn, that is, when there are few nonHorn clauses and/or when the set of all literals that ..."
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Cited by 15 (1 self)
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This paper addresses the problem of computing the minimal models of a given CNF propositional theory. We present two groups of algorithms. Algorithms in the first group are efficient when the theory is almost Horn, that is, when there are few nonHorn clauses and/or when the set of all literals that appear positive in any nonHorn clause is small. Algorithms in the other group are efficient when the theory can be represented as an acyclic network of lowarity relations. Our algorithms suggest several characterizations of tractable subsets for the problem of finding minimal models. 1 Introduction One approach to attacking NPhard problems is to identify islands of tractability in the problem domain and to use their associated algorithms as building blocks for solving hard instances, often approximately. A celebrated example of this approach is the treatment of the propositional satisfiability problem. In this paper, we would like to initiate a similar effort for the problem of findi...
Model Elimination, Logic Programming and Computing Answers
 University of Koblenz
, 1995
"... We demonstrate that theorem provers using model elimination (ME) can be used as answer complete interpreters for disjunctive logic programming. More specifically, we introduce a mechanism for computing answers into the restart variant of ME. Building on this, we develop a new calculus called ancestr ..."
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Cited by 10 (5 self)
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We demonstrate that theorem provers using model elimination (ME) can be used as answer complete interpreters for disjunctive logic programming. More specifically, we introduce a mechanism for computing answers into the restart variant of ME. Building on this, we develop a new calculus called ancestry restart ME. This variant admits a more restrictive regularity restriction than restart ME, and, as a side effect, it is in particular attractive for computing definite answers. The presented calculi can also be used successfully in the context of automated theorem proving. We demonstrate experimentally that it is more difficult to compute (nontrivial) answers to goals, instead of only proving the existence of answers.
A nearHorn Prolog for Compilation
 Computational Logic: Essays in Honor of Alan
, 1989
"... NearHorn Prolog is a logic programming language which extends Prolog to handle nonHorn clauses. It was designed with the goal of minimizing the performance loss for programs with very few nonHorn clauses, while preserving the Prolog format. In this paper, we present a version of nearHorn Prolog ..."
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Cited by 10 (4 self)
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NearHorn Prolog is a logic programming language which extends Prolog to handle nonHorn clauses. It was designed with the goal of minimizing the performance loss for programs with very few nonHorn clauses, while preserving the Prolog format. In this paper, we present a version of nearHorn Prolog that provides a stronger proof system than used by previous nearHorn procedures, and takes advantage of the preprocessing capability of compilers to reduce the accompanying performance penalty. In fact, for a sizable class of nonHorn programs the added inference rule strength incurs no performance penalty at all. In addition to describing this variant, called Inheritance nearHorn Prolog, we prove its soundness and (classical) completeness. 1 Introduction Prolog has been a very successful realization of the concept of logic programming, becoming a serious alternative to LISP as an AI language and enjoying considerable commercial success. However, it has also been clear that a single lan...
Uniform Proofs and Disjunctive Logic Programming (Extended Abstract)
, 1995
"... ) y Gopalan Nadathur z Donald W. Loveland Department of Computer Science Department of Computer Science University of Chicago Duke University 1100 E 58th Street, Chicago, IL 60637 Box 90129, Durham, NC 277080129 gopalan@cs.uchicago.edu dwl@cs.duke.edu Abstract One formulation of the concept of ..."
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Cited by 10 (3 self)
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) y Gopalan Nadathur z Donald W. Loveland Department of Computer Science Department of Computer Science University of Chicago Duke University 1100 E 58th Street, Chicago, IL 60637 Box 90129, Durham, NC 277080129 gopalan@cs.uchicago.edu dwl@cs.duke.edu Abstract One formulation of the concept of logic programming is the notion of Abstract Logic Programming Language, introduced in [8]. Central to that definition is uniform proof, which enforces the requirements of inference direction, including goaldirectedness, and the duality of readings, declarative and procedural. We use this technology to investigate Disjunctive Logic Programming (DLP), an extension of traditional logic programming that permits disjunctive program clauses. This extension has been considered by some to be inappropriately identified with logic programming because the indefinite reasoning introduced by disjunction violates the goaloriented search directionality central to logic programming. We overcome this crit...
Computing Answers with Model Elimination
, 1997
"... We demonstrate that theorem provers using model elimination (ME) can be used as answercomplete interpreters for disjunctive logic programming. More specifically, we introduce a mechanism for computing answers into the restart variant of ME. Building on this we develop a new calculus called ancestry ..."
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Cited by 9 (2 self)
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We demonstrate that theorem provers using model elimination (ME) can be used as answercomplete interpreters for disjunctive logic programming. More specifically, we introduce a mechanism for computing answers into the restart variant of ME. Building on this we develop a new calculus called ancestry restart ME. This variant admits a more restrictive regularity restriction than restart ME, and, as a side effect, it is in particular attractive for computing definite answers. The presented calculi can also be used successfully in the context of automated theorem proving. We demonstrate experimentally that it is more difficult to compute (nontrivial) answers to goals, instead of only proving the existence of answers. Keywords. Automated reasoning; theorem proving; model elimination; logic programming; computing answers. In first order automatic theorem proving one is interested in the question whether a given formula follows logically from a set of axioms. This is a rather artificial t...
Analysis and Transformation of Proof Procedures
, 1994
"... Automated theorem proving has made great progress during the last few decades. Proofs of more and more difficult theorems are being found faster and faster. However, the exponential increase in the size of the search space remains for many theorem proving problems. Logic program analysis and transfo ..."
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Cited by 8 (2 self)
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Automated theorem proving has made great progress during the last few decades. Proofs of more and more difficult theorems are being found faster and faster. However, the exponential increase in the size of the search space remains for many theorem proving problems. Logic program analysis and transformation techniques have also made progress during the last few years and automated theorem proving can benefit from these techniques if they can be made applicable to general theorem proving problems. In this thesis we investigate the applicability of logic program analysis and transformation techniques to automated theorem proving. Our aim is to speed up theorem provers by avoiding useless search. This is done by detecting and deleting parts of the theorem prover and theory under consideration that are not needed for proving a given formula. The analysis and transformation techniques developed for logic programs can be applied in automated theorem proving via a programming technique called ...
Refinements of Theory Model Elimination and a Variant without Contrapositives
 University of Koblenz, Institute for Computer Science
, 1994
"... Theory Reasoning means to buildin certain knowledge about a problem domain into a deduction system or calculus, which is in our case model elimination. Several versions of theory model elimination (TME) calculi are presented and proven complete: on the one hand we have highly restricted versions of ..."
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Cited by 8 (6 self)
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Theory Reasoning means to buildin certain knowledge about a problem domain into a deduction system or calculus, which is in our case model elimination. Several versions of theory model elimination (TME) calculi are presented and proven complete: on the one hand we have highly restricted versions of total and partial TME. These restrictions allow (1) to keep fewer path literals in extension steps than in related calculi, and (2) discard proof attempts with multiple occurrences of literals along a path (i.e. regularity holds). On the other hand, we obtain by small modifications to TME versions which do not need contrapositives (a la NearHorn Prolog). We show that regularity can be adapted for these versions. The independence of the goal computation rule holds for all variants. Comparative runtime results for our PTTPimplementations are supplied. 1 Introduction The model elimination calculus (ME calculus) has been developed already in the early days of automated theorem proving [Lovel...