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Model Streaming for Distributed Multi-Context Systems ⋆
"... Abstract. Multi-Context Systems (MCS) are instances of a nonmonotonic formalism for interlinking heterogeneous knowledge bases in a way such that the information flow is in equilibrium. Recently, algorithms for evaluating distributed MCS have been proposed which compute global system models, called ..."
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Abstract. Multi-Context Systems (MCS) are instances of a nonmonotonic formalism for interlinking heterogeneous knowledge bases in a way such that the information flow is in equilibrium. Recently, algorithms for evaluating distributed MCS have been proposed which compute global system models, called equilibria, by local computation and model exchange. Unfortunately, they suffer from a bottleneck that stems from the way models are exchanged, which limits the applicability to situations with small information interfaces. To push MCS to more realistic and practical scenarios, we present a novel algorithm that computes at most k ≥ 1 models of an MCS using asynchronous communication. Models are wrapped into packages, and contexts in an MCS continuously stream packages to generate at most k models at the root of the system. We have implemented this algorithm in a new solver for distributed MCS, and show promising experimental results. 1
Nested hex-programs
- CoRR
"... Abstract. Answer-Set Programming (ASP) is an established declarative programming paradigm. How-ever, classical ASP lacks subprogram calls as in procedural programming, and access to external computations (like remote procedure calls) in general. The feature is desired for increasing modularity and—a ..."
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Abstract. Answer-Set Programming (ASP) is an established declarative programming paradigm. How-ever, classical ASP lacks subprogram calls as in procedural programming, and access to external computations (like remote procedure calls) in general. The feature is desired for increasing modularity and—assuming proper access in place—(meta-)reasoning over subprogram results. While HEX-programs extend classical ASP with external source access, they do not support calls of (sub-)programs upfront. We present nested HEX-programs, which extend HEX-programs to serve the desired feature, in a user-friendly manner. Notably, the answer sets of called sub-programs can be individually accessed. This is particularly useful for applications that need to reason over answer sets like belief set merging, user-defined aggregate functions, or preferences of answer sets. 1
Semantic Reasoning with SPARQL in Heterogeneous Multi-Context Systems ⋆
"... Abstract. Multi-Context Systems (MCSs) are an expressive framework for interlinking heterogeneous knowledge systems, called contexts. Possible contexts are ontologies, relational databases, logic programs, RDF triplestores, etc. MCSs contain bridge rules to specify knowledge exchange between context ..."
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Abstract. Multi-Context Systems (MCSs) are an expressive framework for interlinking heterogeneous knowledge systems, called contexts. Possible contexts are ontologies, relational databases, logic programs, RDF triplestores, etc. MCSs contain bridge rules to specify knowledge exchange between contexts. We extend the MCS formalism and propose SPARQL-MCS where knowledge exchange is specified in the style of SPARQL CONSTRUCT queries. Different from previous approaches to variables in MCSs, we do not impose any restrictions on contexts. To achieve this, we introduce a general approach for variable substitutions in heterogeneous systems. We define syntax and semantics of SPARQL-MCS and investigate fixpoint evaluation of monotonic MCSs. 1
Advancing Multi-Context Systems by Inconsistency Management ⋆
, 1107
"... Abstract. Multi-Context Systems are an expressive formalism to model (possibly) non-monotonic information exchange between heterogeneous knowledge bases. Such information exchange, however, often comeswith unforseen side-effects leading to violation of constraints, making the system inconsistent, an ..."
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Abstract. Multi-Context Systems are an expressive formalism to model (possibly) non-monotonic information exchange between heterogeneous knowledge bases. Such information exchange, however, often comeswith unforseen side-effects leading to violation of constraints, making the system inconsistent, and thus unusable. Although there are many approaches to assess and repair a single inconsistent knowledge base, the heterogeneous nature of Multi-Context Systems poses problems which have not yet been addressed in a satisfying way: How to identify and explain a inconsistency that spreads over multiple knowledge bases with different logical formalisms (e.g., logic programs and ontologies)? What are the causes of inconsistency if inference/information exchange is nonmonotonic (e.g., absent information as cause)? How to deal with inconsistency if access to knowledge bases is restricted (e.g., companies exchange information, but do not allow arbitrary modifications to their knowledge bases)? Many traditional approaches solely aim for a consistent system, but automatic removal of inconsistency is not always desireable. Therefore a human operator has to be supported in finding the erroneous parts contributing to the inconsistency. In my thesis those issues will be adressed mainly from a foundational perspective, while our research project also provides algorithms and prototype implementations. 1
Promoting Modular Nonmonotonic Logic Programs ∗
"... Modularity in Logic Programming has gained much attention over the past years. To date, many formalisms have been proposed that feature various aspects of modularity. In this paper, we present our current work on Modular Nonmonotonic Logic Programs (MLPs), which are logic programs under answer set s ..."
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Modularity in Logic Programming has gained much attention over the past years. To date, many formalisms have been proposed that feature various aspects of modularity. In this paper, we present our current work on Modular Nonmonotonic Logic Programs (MLPs), which are logic programs under answer set semantics with modules that have contextualized input provided by other modules. Moreover, they allow for (mutually) recursive module calls. We pinpoint issues that are present in such cyclic module systems and highlight how MLPs addresses them.
Modularity in the Rule Interchange Format
"... Abstract. The adoption of standards by the knowledge representation and logic programming communities is essential for their visibility and impact. The Rule Interchange Format is a fundamental effort in this direction that should be supported by users, developers and theoreticians. For this reason, ..."
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Abstract. The adoption of standards by the knowledge representation and logic programming communities is essential for their visibility and impact. The Rule Interchange Format is a fundamental effort in this direction that should be supported by users, developers and theoreticians. For this reason, it is essential to the community to discuss the recommendations published by the W3C RIF Working Group. In particular, this paper presents the semantics of Rule Interchange Format (RIF) of multidocuments, analyses it and some deficiencies are elicited. A more general approach is proposed as an alternative semantics for multi-documents. As a side important result, some relevant problems in the semantics of RIF-FLD are also discussed and possible ways out are proposed.
Embeddings of Simple Modular Extended RDF
"... Abstract. The Extended Resource Description Framework has been proposed to equip RDF graphs with weak and strong negation, as well as derivation rules, increasing the expressiveness of ordinary RDF graphs. In parallel, the Modular Web framework enables collaborative and controlled reasoning in the S ..."
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Abstract. The Extended Resource Description Framework has been proposed to equip RDF graphs with weak and strong negation, as well as derivation rules, increasing the expressiveness of ordinary RDF graphs. In parallel, the Modular Web framework enables collaborative and controlled reasoning in the Semantic Web. In this paper we exploit the use of the Modular Web framework to specify the modular semantics for Extended Resource Description Framework ontologies. 1
Distributed Evaluation of Nonmonotonic Multi-context Systems
"... Multi-context Systems (MCSs) are a formalism for systems consisting of knowledge bases (possibly heterogeneous and non-monotonic) that are interlinked via bridge rules, where the global system semantics emerges from the local semantics of the knowledge bases (also called “contexts”) in an equilibriu ..."
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Multi-context Systems (MCSs) are a formalism for systems consisting of knowledge bases (possibly heterogeneous and non-monotonic) that are interlinked via bridge rules, where the global system semantics emerges from the local semantics of the knowledge bases (also called “contexts”) in an equilibrium. While MCSs and related formalisms are inherently targeted for distributed set-tings, no truly distributed algorithms for their evaluation were available. We address this short-coming and present a suite of such algorithms which includes a basic algorithm DMCS, an ad-vanced version DMCSOPT that exploits topology-based optimizations, and a streaming algorithm DMCS-STREAMING that computes equilibria in packages of bounded size. The algorithms be-have quite differently in several respects, as experienced in thorough experimental evaluation of a system prototype. From the experimental results, we derive a guideline for choosing the appropriate algorithm and running mode in particular situations, determined by the parameter settings. 1.
1 EMBEDDING DESCRIPTION LOGIC PROGRAMS INTO DEFAULT LOGIC Embedding Description Logic Programs into Default Logic
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