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Thomas Eiter - One of the best experts on this subject based on the ideXlab platform.
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LPNMR - Pushing efficient evaluation of HEX programs by modular decomposition
Logic Programming and Nonmonotonic Reasoning, 2011Co-Authors: Thomas Eiter, Thomas Krennwallner, Michael Fink, Giovambattista Ianni, Peter SchüllerAbstract:The evaluation of Logic programs with access to external knowledge sources requires to interleave external computation and model building. Deciding where and how to stop with one task and proceed with the next is a difficult problem, and existing approaches have severe scalability limitations in many real-world application scenarios. We introduce a new approach for organizing the evaluation of Logic programs with external knowledge sources and describe a configurable framework for dividing the non-ground program into overlapping possiblysmaller parts called evaluation units. These units will then be processed by interleaving external evaluations and model building according to an evaluation and a model graph, and by combining intermediate results. Experiments with our prototype implementation show a significant improvement of this technique compared to existing approaches. Interestingly, even for Ordinary Logic programs (with no external access), our decomposition approach speeds up existing state of the art ASP solvers in some cases, showing its potential for wider usage.
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Well-founded semantics for description Logic programs in the semantic web
ACM Transactions on Computational Logic, 2011Co-Authors: Thomas Eiter, Thomas Lukasiewicz, Giovambattista Ianni, Roman SchindlauerAbstract:The realization of the Semantic Web vision, in which computational Logic has a prominent role, has stimulated a lot of research on combining rules and ontologies, which are formulated in different formalisms. In particular, combining Logic programming with the Web Ontology Language (OWL), which is a standard based on description Logics, emerged as an important issue for linking the Rules and Ontology Layers of the Semantic Web. Nonmonotonic description Logic programs (dl-programs) were introduced for such a combination, in which a pair (L,P) of a description Logic knowledge base L and a set of rules P with negation as failure is given a model-based semantics that generalizes the answer set semantics of Logic programs. In this article, we reconsider dl-programs and present a well-founded semantics for them as an analog for the other main semantics of Logic programs. It generalizes the canonical definition of the well-founded semantics based on unfounded sets, and, as we show, lifts many of the well-known properties from Ordinary Logic programs to dl-programs. Among these properties, our semantics amounts to a partial model approximating the answer set semantics, which yields for positive and stratified dl-programs, a total model coinciding with the answer set semantics; it has polynomial data complexity provided the access to the description Logic knowledge base is polynomial; under suitable restrictions, it has lower complexity and even first-order rewritability is achievable. The results add to previous evidence that dl-programs are a versatile and robust combination approach, which moreover is implementable using legacy engines.
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Datalog - First-Order encodings for modular nonmonotonic datalog programs
Datalog Reloaded, 2010Co-Authors: Minh Dao-tran, Michael Fink, Thomas Eiter, Thomas KrennwallnerAbstract:Recently Modular Nonmonotonic Logic Programs (MLP) have been introduced which incorporate a call-by-value mechanism and allow for unrestricted calls between modules, including mutual and self recursion, as an approach to provide module constructs akin to those in conventional programming in Nonmonotonic Logic Programming under Answer Set Semantics. This paper considers MLPs in a Datalog setting and provides characterizations of their answers sets in terms of classical (Herbrand) models of a first-order formula, extending a line of research for Ordinary Logic programs. To this end, we lift the well-known loop formulas method to MLPs, and we also consider the recent ordered completion approach that avoids explicit construction of loop formulas using auxiliary predicates. Independent of computational perspectives, the novel characterizations widen our understanding of MLPs and they may prove useful for semantic investigations.
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ICLP - Modular Nonmonotonic Logic Programming Revisited
Logic Programming, 2009Co-Authors: Minh Tran, Thomas Eiter, Michael Fink, Thomas KrennwallnerAbstract:Recently, enabling modularity aspects in Answer Set Programming (ASP) has gained increasing interest to ease the composition of program parts to an overall program. In this paper, we focus on modular nonmonotonic Logic programs (MLP) under the answer set semantics, whose modules may have contextually dependent input provided by other modules. Moreover, (mutually) recursive module calls are allowed. We define a model-theoretic semantics for this extended setting, show that many desired properties of Ordinary Logic programming generalize to our modular ASP, and determine the computational complexity of the new formalism. We investigate the relationship of modular programs to disjunctive Logic programs with well-defined input/output interface (DLP-functions) and show that they can be embedded into MLPs.
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Modular Nonmonotonic Logic Programming Revisited
Logic Programming, 2009Co-Authors: Minh Dao-tran, Michael Fink, Thomas Eiter, Thomas KrennwallnerAbstract:Recently, enabling modularity aspects in Answer Set Programming (ASP) has gained increasing interest to ease the composition of program parts to an overall program. In this paper, we focus on modular nonmonotonic Logic programs (MLP) under the answer set semantics, whose modules may have contextually dependent input provided by other modules. Moreover, (mutually) recursive module calls are allowed. We define a model-theoretic semantics for this extended setting, show that many desired properties of Ordinary Logic programming generalize to our modular ASP, and determine the computational complexity of the new formalism. We investigate the relationship of modular programs to disjunctive Logic programs with well-defined input/output interface (DLP-functions) and show that they can be embedded into MLPs.
Thomas Krennwallner - One of the best experts on this subject based on the ideXlab platform.
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LPNMR - Pushing efficient evaluation of HEX programs by modular decomposition
Logic Programming and Nonmonotonic Reasoning, 2011Co-Authors: Thomas Eiter, Thomas Krennwallner, Michael Fink, Giovambattista Ianni, Peter SchüllerAbstract:The evaluation of Logic programs with access to external knowledge sources requires to interleave external computation and model building. Deciding where and how to stop with one task and proceed with the next is a difficult problem, and existing approaches have severe scalability limitations in many real-world application scenarios. We introduce a new approach for organizing the evaluation of Logic programs with external knowledge sources and describe a configurable framework for dividing the non-ground program into overlapping possiblysmaller parts called evaluation units. These units will then be processed by interleaving external evaluations and model building according to an evaluation and a model graph, and by combining intermediate results. Experiments with our prototype implementation show a significant improvement of this technique compared to existing approaches. Interestingly, even for Ordinary Logic programs (with no external access), our decomposition approach speeds up existing state of the art ASP solvers in some cases, showing its potential for wider usage.
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Datalog - First-Order encodings for modular nonmonotonic datalog programs
Datalog Reloaded, 2010Co-Authors: Minh Dao-tran, Michael Fink, Thomas Eiter, Thomas KrennwallnerAbstract:Recently Modular Nonmonotonic Logic Programs (MLP) have been introduced which incorporate a call-by-value mechanism and allow for unrestricted calls between modules, including mutual and self recursion, as an approach to provide module constructs akin to those in conventional programming in Nonmonotonic Logic Programming under Answer Set Semantics. This paper considers MLPs in a Datalog setting and provides characterizations of their answers sets in terms of classical (Herbrand) models of a first-order formula, extending a line of research for Ordinary Logic programs. To this end, we lift the well-known loop formulas method to MLPs, and we also consider the recent ordered completion approach that avoids explicit construction of loop formulas using auxiliary predicates. Independent of computational perspectives, the novel characterizations widen our understanding of MLPs and they may prove useful for semantic investigations.
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ICLP - Modular Nonmonotonic Logic Programming Revisited
Logic Programming, 2009Co-Authors: Minh Tran, Thomas Eiter, Michael Fink, Thomas KrennwallnerAbstract:Recently, enabling modularity aspects in Answer Set Programming (ASP) has gained increasing interest to ease the composition of program parts to an overall program. In this paper, we focus on modular nonmonotonic Logic programs (MLP) under the answer set semantics, whose modules may have contextually dependent input provided by other modules. Moreover, (mutually) recursive module calls are allowed. We define a model-theoretic semantics for this extended setting, show that many desired properties of Ordinary Logic programming generalize to our modular ASP, and determine the computational complexity of the new formalism. We investigate the relationship of modular programs to disjunctive Logic programs with well-defined input/output interface (DLP-functions) and show that they can be embedded into MLPs.
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Modular Nonmonotonic Logic Programming Revisited
Logic Programming, 2009Co-Authors: Minh Dao-tran, Michael Fink, Thomas Eiter, Thomas KrennwallnerAbstract:Recently, enabling modularity aspects in Answer Set Programming (ASP) has gained increasing interest to ease the composition of program parts to an overall program. In this paper, we focus on modular nonmonotonic Logic programs (MLP) under the answer set semantics, whose modules may have contextually dependent input provided by other modules. Moreover, (mutually) recursive module calls are allowed. We define a model-theoretic semantics for this extended setting, show that many desired properties of Ordinary Logic programming generalize to our modular ASP, and determine the computational complexity of the new formalism. We investigate the relationship of modular programs to disjunctive Logic programs with well-defined input/output interface (DLP-functions) and show that they can be embedded into MLPs.
Hans Tompits - One of the best experts on this subject based on the ideXlab platform.
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KR - Notions of strong equivalence for Logic programs with ordered disjunction
2008Co-Authors: Wolfgang Faber, Hans Tompits, Stefan WoltranAbstract:Ordered disjunctions have been introduced as a simple, yet expressive approach for representing preferential knowledge by means of Logic programs. The semantics for the resulting language is based on the answer-set semantics, but comes in different variants, depending on the particular interpretation of preference aggregation associated to the ordered disjunction connective. While in standard answer-set programming the question of when a program is to be considered equivalent to another received increasing attention in recent years, this problem has not been addressed for programs with ordered disjunctions so far. In this paper, we discuss the concept of strong equivalence in this setting. We introduce different versions of strong equivalence for programs with ordered disjunctions and provide model-theoretic characterisations, extending well-known ones for strong equivalence between Ordinary Logic programs. Furthermore, we discuss the relationships between the proposed notions and study their computational complexity.
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Combining answer set programming with description Logics for the Semantic Web
Artificial Intelligence, 2008Co-Authors: Thomas Eiter, Roman Schindlauer, Thomas Lukasiewicz, Giovambattista Ianni, Hans TompitsAbstract:We propose a combination of Logic programming under the answer set semantics with the description Logics SHIF(D) and SHOIN(D), which underly the Web ontology languages OWL Lite and OWL DL, respectively. To this end, we introduce description Logic programs (or dl-programs), which consist of a description Logic knowledge base L and a finite set P of description Logic rules (or dl-rules). Such rules are similar to usual rules in nonmonotonic Logic programs, but they may also contain queries to L, possibly under default negation, in their bodies. They allow for building rules on top of ontologies but also, to a limited extent, building ontologies on top of rules. We define a suite of semantics for various classes of dl-programs, which conservatively extend the standard semantics of the respective classes and coincide with it in absence of a description Logic knowledge base. More concretely, we generalize positive, stratified, and arbitrary normal Logic programs to dl-programs, and define a Herbrand model semantics for them. We show that they have similar properties as Ordinary Logic programs, and also provide fixpoint characterizations in terms of (iterated) consequence operators. For arbitrary dl-programs, we define answer sets by generalizing Gelfond and Lifschitz's notion of a transform, leading to a strong and a weak answer set semantics, which are based on reductions to the semantics of positive dl-programs and Ordinary positive Logic programs, respectively. We also show how the weak answer sets can be computed utilizing answer sets of Ordinary normal Logic programs. Furthermore, we show how some advanced reasoning tasks for the Semantic Web, including different forms of closed-world reasoning and default reasoning, as well as DL-safe rules, can be realized on top of dl-programs. Finally, we give a precise picture of the computational complexity of dl-programs, and we describe efficient algorithms and a prototype implementation of dl-programs which is available on the Web.
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Characterizing Notions of Strong Equivalence for Logic Programs with Ordered Disjunctions
2007Co-Authors: Wolfgang Faber, Hans Tompits, Stefan WoltranAbstract:Ordered disjunctions have recently been introduced as a simple, yet expressive approach for representing preferential knowledge by means of Logic programs. The semantics for the resulting language is based on the answer-set semantics, but comes in dierent avors, depending on the particular notion of preference associated to the disjunction connective. While in standard answer-set programming, the question of when a program is to be considered equivalent to another received increasing attention in recent years, this problem has not been addressed for programs with ordered disjunctions so far. In this paper, we discuss the concept of strong equivalence in the latter setting. We introduce dierent versions of strong equivalence for programs with ordered disjunctions and provide model-theoretic characterizations, extending well-known ones for strong equivalence between Ordinary Logic programs. Furthermore, we discuss interesting relations between the proposed notions.
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combining answer set programming with description Logics for the semantic web
Principles of Knowledge Representation and Reasoning, 2004Co-Authors: Thomas Eiter, Roman Schindlauer, Thomas Lukasiewicz, Hans TompitsAbstract:Towards the integration of rules and ontologies in the Semantic Web, we propose a combination of Logic programming under the answer set semantics with the description Logics SHIF(D) and SHOIN(D), which underly the Web ontology languages OWL Lite and OWL DL, respectively. This combination allows for building rules on top of ontologies but also, to a limited extent, building ontologies on top of rules. We introduce description Logic programs (dl-programs), which consist of a description Logic knowledge base L and a finite set of description Logic rules (dl-rules) P. Such rules are similar to usual rules in Logic programs with negation as failure, but may also contain queries to L, possibly default negated, in their bodies. We define Herbrand models for dl-programs, and show that satisfiable positive dl-programs have a unique least Her-brand model. More generally, consistent stratified dl-programs can be associated with a unique minimal Her-brand model that is characterized through iterative least Herbrand models. We then generalize the (unique) minimal Herbrand model semantics for positive and stratified dl-programs to a strong answer set semantics for all dl-programs, which is based on a reduction to the least model semantics of positive dl-programs. We also define a weak answer set semantics based on a reduction to the answer sets of Ordinary Logic programs. Strong answer sets are weak answer sets, and both properly generalize answer sets of Ordinary normal Logic programs. We then give fixpoint characterizations for the (unique) minimal Herbrand model semantics of positive and stratified dl-programs, and show how to compute these models by finite fixpoint iterations. Furthermore, we give a precise picture of the complexity of deciding strong and weak answer set existence for a dl-program.
Benjamin N Grosof - One of the best experts on this subject based on the ideXlab platform.
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Representing E-Commerce Rules Via Situated Courteous Logic Programs in RuleML
Electronic Commerce Research and Applications, 2004Co-Authors: Benjamin N GrosofAbstract:We give an overview of current efforts to standardize e-business rules knowledge representation (KR) in XML as part of the Semantic Web. We focus especially on the design approach and criteria of RuleML, an emerging standard that we co-lead. We discuss the issues of standardization and Webizing which RuleML addresses. We extend, for the first time, RuleML’s definition from the Ordinary Logic programs KR to situated courteous Logic programs (SCLP), an expressively general KR that supports prioritized conflict handling and procedural attachments for actions and queries. We give an overview of our prototype SweetRules, (Semantic WEb Enabling Technology – Rules component), a set of tools which enable, for the first time, communication and inferencing of e-business rules represented in SCLP RuleML. We illustrate SCLP RuleML by giving example rulesets from the realm of e-commerce business policies in supply chain management. 1
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Delegation Logic: A Logic-based approach to distributed authorization
ACM Transactions on Information and System Security, 2003Co-Authors: Benjamin N Grosof, Joan FeigenbaumAbstract:We address the problem of authorization in large-scale, open, distributed systems. Authorization decisions are needed in electronic commerce, mobile-code execution, remote resource sharing, privacy protection, and many other applications. We adopt the trust-management approach, in which "authorization" is viewed as a "proof-of-compliance" problem: Does a set of credentials prove that a request complies with a policy?We develop a Logic-based language, called Delegation Logic (DL), to represent policies, credentials, and requests in distributed authorization. In this paper, we describe D1LP, the monotonic version of DL. D1LP extends the Logic-programming (LP) language Datalog with expressive delegation constructs that feature delegation depth and a wide variety of complex principals (including, but not limited to, k-out-of-n thresholds). Our approach to defining and implementing D1LP is based on tractably compiling D1LP programs into Ordinary Logic programs (OLPs). This compilation approach enables D1LP to be implemented modularly on top of existing technologies for OLP, for example, Prolog.As a trust-management language, D1LP provides a concept of proof-of-compliance that is founded on well-understood principles of Logic programming and knowledge representation. D1LP also provides a Logical framework for studying delegation.
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IEEE Symposium on Security and Privacy - A practically implementable and tractable delegation Logic
SSRN Electronic Journal, 2000Co-Authors: Benjamin N Grosof, Joan FeigenbaumAbstract:We address the goal of making Delegation Logic (DL) into a practically implementable and tractable trust management system. DL (N. Li et al., 1999) is a Logic based knowledge representation (i.e., language) for authorization in large scale, open, distributed systems. DL inferencing is computationally intractable and highly impractical to implement. We introduce a new version of Delegation Logic that remedies these difficulties. To achieve this, we impose a syntactic restriction and redefine the semantics somewhat. We show that, for this revised version of DL, inferencing is computationally tractable under the same commonly met restrictions for which Ordinary Logic Programs (OLP) inferencing is tractable (e.g., Datalog and bounded number of Logical variables per rule). We give an implementation architecture for this version of DL; it uses a delegation compiler from DL to OLP and can modularly exploit a variety of existing OLP inference engines. As proof of concept, we have implemented a large expressive subset of this version of DL, using this architecture.
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Issues in Agent Communication - An Approach to Using XML and a Rule-Based Content Language with an Agent Communication Language
Issues in Agent Communication, 2000Co-Authors: Benjamin N Grosof, Yannis LabrouAbstract:We argue for an XML encoding of FIPA Agent Communication Language (ACL), and give an alpha version of it, called Agent Communication Markup Language (ACML), which we have implemented. The XML approach facilitates: (a) developing/maintaining parsers, integrating with WWW-world software engineering, and (b) the enriching capability to (hyper-)link to ontologies and other extra information. The XML approach applies similarly to KQML as well. Motivated by the importance of the content language aspect of agent communication, we focus in particular on business rules as a form of content that is important in e-commerce applications such as bidding negotiations. A leading candidate content language for business rules is Knowledge Interchange Format (KIF), which is currently in the ANSI standards committee process. We observe several major practical shortcomings of KIF as a content language for business rules in e-commerce. We argue instead for a knowledge representation (KR) approach based on Courteous Logic Programs (CLP) that overcomes several of KIF’s representational limitations, and argue for this CLP approach, e.g., for its Logical non-monotonicity and its computational practicality. CLP is a previous KR that expressively extends declarative Ordinary Logic programs cf. Prolog; it includes negation-as-failure plus prioritized conflict handling. We argue for an XML encoding of business rules content, and give an alpha version of it, called Business Rules Markup Language (BRML), which we have implemented. BRML can express both CLP and a subset of KIF (i.e., of first-order Logic) that overlaps with CLP. BRML expressively both extends and complements KIF. The overall advantages of an XML approach to content language are similar to those for the XML approach to ACL, and indeed complements the latter since content is carried within ACL messages. We have implemented both ACML and BRML/CLP; a free alpha prototype of BRML/CLP, called IBM CommonRules, was released on the Web in July of 1999.
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diplomat compiling prioritized default rules into Ordinary Logic programs for e commerce applications
National Conference on Artificial Intelligence, 1999Co-Authors: Benjamin N GrosofAbstract:Rules promise to be widely useful in Internet electronic commerce. Declarative prioritized default rule knowledge representations offer the advantage of handling conflicts that arise in updating rule sets, but have as yet had little practical deployment. DIPLOMAT is a Java library that embodies a new approach to the implementation of such prioritized default rules: to compile them into Ordinary Logic programs (LP's) cf. pure Prolog. We apply the approach to a newly generalized version of courteous LP's, a semantically attractive and computationally tractable form of prioritized default rules. Compilation enables courteous LP's functionality to be added modularly to Ordinary LP rule engines, via a preprocessor, with tractable computational overhead. This takes a long step towards actual deployment of prioritized-default knowledge representation in commercially fielded technology and applications.We give in the demo storyboard an automated example e-commerce application scenario: inferencing in a 70-rule courteous LP that represents personalized pricing and promotions on a bookstore's Web storefront.
Michael Fink - One of the best experts on this subject based on the ideXlab platform.
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LPNMR - Pushing efficient evaluation of HEX programs by modular decomposition
Logic Programming and Nonmonotonic Reasoning, 2011Co-Authors: Thomas Eiter, Thomas Krennwallner, Michael Fink, Giovambattista Ianni, Peter SchüllerAbstract:The evaluation of Logic programs with access to external knowledge sources requires to interleave external computation and model building. Deciding where and how to stop with one task and proceed with the next is a difficult problem, and existing approaches have severe scalability limitations in many real-world application scenarios. We introduce a new approach for organizing the evaluation of Logic programs with external knowledge sources and describe a configurable framework for dividing the non-ground program into overlapping possiblysmaller parts called evaluation units. These units will then be processed by interleaving external evaluations and model building according to an evaluation and a model graph, and by combining intermediate results. Experiments with our prototype implementation show a significant improvement of this technique compared to existing approaches. Interestingly, even for Ordinary Logic programs (with no external access), our decomposition approach speeds up existing state of the art ASP solvers in some cases, showing its potential for wider usage.
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JELIA - A Logical semantics for description Logic programs
Logics in Artificial Intelligence, 2010Co-Authors: Michael Fink, David PearceAbstract:We present a new semantics for Description Logic programs [1] (dl-programs) that combine reasoning about ontologies in description Logics with non-monotonic rules interpreted under answer set semantics. Our semantics is equivalent to that of [1], but is more Logical in style, being based on the Logic QHT of quantified here-and-there that provides a foundation for Ordinary Logic programs under answer set semantics and removes the need for program reducts. Here we extend the concept of QHT-model to encompass dl-programs. As an application we characterise some Logical relations between dl-programs, by mating the idea of QHT-equivalence with the concept of query inseparability taken from description Logics.
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Datalog - First-Order encodings for modular nonmonotonic datalog programs
Datalog Reloaded, 2010Co-Authors: Minh Dao-tran, Michael Fink, Thomas Eiter, Thomas KrennwallnerAbstract:Recently Modular Nonmonotonic Logic Programs (MLP) have been introduced which incorporate a call-by-value mechanism and allow for unrestricted calls between modules, including mutual and self recursion, as an approach to provide module constructs akin to those in conventional programming in Nonmonotonic Logic Programming under Answer Set Semantics. This paper considers MLPs in a Datalog setting and provides characterizations of their answers sets in terms of classical (Herbrand) models of a first-order formula, extending a line of research for Ordinary Logic programs. To this end, we lift the well-known loop formulas method to MLPs, and we also consider the recent ordered completion approach that avoids explicit construction of loop formulas using auxiliary predicates. Independent of computational perspectives, the novel characterizations widen our understanding of MLPs and they may prove useful for semantic investigations.
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ICLP - Modular Nonmonotonic Logic Programming Revisited
Logic Programming, 2009Co-Authors: Minh Tran, Thomas Eiter, Michael Fink, Thomas KrennwallnerAbstract:Recently, enabling modularity aspects in Answer Set Programming (ASP) has gained increasing interest to ease the composition of program parts to an overall program. In this paper, we focus on modular nonmonotonic Logic programs (MLP) under the answer set semantics, whose modules may have contextually dependent input provided by other modules. Moreover, (mutually) recursive module calls are allowed. We define a model-theoretic semantics for this extended setting, show that many desired properties of Ordinary Logic programming generalize to our modular ASP, and determine the computational complexity of the new formalism. We investigate the relationship of modular programs to disjunctive Logic programs with well-defined input/output interface (DLP-functions) and show that they can be embedded into MLPs.
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Modular Nonmonotonic Logic Programming Revisited
Logic Programming, 2009Co-Authors: Minh Dao-tran, Michael Fink, Thomas Eiter, Thomas KrennwallnerAbstract:Recently, enabling modularity aspects in Answer Set Programming (ASP) has gained increasing interest to ease the composition of program parts to an overall program. In this paper, we focus on modular nonmonotonic Logic programs (MLP) under the answer set semantics, whose modules may have contextually dependent input provided by other modules. Moreover, (mutually) recursive module calls are allowed. We define a model-theoretic semantics for this extended setting, show that many desired properties of Ordinary Logic programming generalize to our modular ASP, and determine the computational complexity of the new formalism. We investigate the relationship of modular programs to disjunctive Logic programs with well-defined input/output interface (DLP-functions) and show that they can be embedded into MLPs.