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- item-1 hasContent luigi-iannone.
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- item-2 hasContent ignazio-palmisano.
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- 57 creator amadis-martinez.
- 57 creator axel-polleres.
- 57 creator edna-ruckhaus.
- 57 creator javier-sierra.
- 57 creator maria-esther-vidal.
- 57 creator tomas-lampo.
- 57 type InProceedings.
- 57 label "On the Efficiency of Joining Group Patterns in SPARQL Queries".
- 57 sameAs 57.
- 57 abstract "In SPARQL queries, the combination of triple patterns is expressed by using shared variables across patterns. Based on this characterization, basic graph patterns in a SPARQL query can be partitioned into groups of acyclic pattern combinations that share exactly one variable, or star-shaped groups. We observe that the number of triples in a group is proportional to the number of individuals that play the role of the subject or the object; however, depending on the degree of participation of the subject individuals in the properties, a group could be not much larger than a class or type to which the subject or object belongs. Thus, it may be significantly more efficient to independently evaluate each of the groups, and then merge the resulting sets, than linearly joining all triples in a basic graph pattern. Based on these properties of star-shaped groups, we have developed query optimization and evaluation techniques. We have conducted an empirical analysis on the benefits of the optimization and evaluation techniques in several SPARQL query engines. We observe that our proposed techniques are able to speed up query evaluation time for join queries with star-shaped patterns by at least one order of magnitude.".
- 57 hasAuthorList authorList.
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- 57 keyword "Cost Models".
- 57 keyword "Query Optimization".
- 57 keyword "RDF Query Engines".
- 57 keyword "SPARQL".
- 57 title "On the Efficiency of Joining Group Patterns in SPARQL Queries".
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- item-1 hasContent maria-esther-vidal.
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- 66 creator joerg-puehrer.
- 66 creator stijn-heymans.
- 66 creator thomas-eiter.
- 66 type InProceedings.
- 66 label "Dealing with Inconsistency when Combining Ontologies and Rules using DL-Programs".
- 66 sameAs 66.
- 66 abstract "Description Logic Programs (DL-programs) have been introduced as a realization of combined ontological and rule-based reasoning in the context of the Semantic Web. A DL-program loosely combines a Description Logic (DL) ontology with a non-monotonic logic program (LP) such that dedicated atoms in the LP, called DL-atoms, allow for a bidirectional flow of knowledge between the two components. Unfor- tunately, the information sent from the LP-part to the DL-part might cause an inconsistency in the latter, leading to the trivial satisfaction of every query. As a consequence, in such a case, the answer sets that define the semantics of the DL-program may contain spoiled informa- tion influencing the overall deduction. For avoiding unintuitive answer sets, we introduce a refined semantics for DL-programs that is sensitive for inconsistency caused by the combination of DL and LP, and dynam- ically deactivates rules whenever such an inconsistency would arise. We analyze the complexity of the new semantics, discuss implementational issues and introduce an adequate notion of stratification that guarantees uniqueness of answer sets.".
- 66 hasAuthorList authorList.
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- 66 keyword "DL-Programs".
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- 66 keyword "integration of rules and ontologies".
- 66 title "Dealing with Inconsistency when Combining Ontologies and Rules using DL-Programs".
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- 68 creator daniel-olmedilla.
- 68 creator philipp-kaerger.
- 68 creator piero-bonatti.
- 68 type InProceedings.
- 68 label "Reactive Policies for the Semantic Web".
- 68 sameAs 68.