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ESWC 2013 Poster: Representing and Querying Negative Knowledge in RDF

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Typically, only positive data can be represented in RDF. However, negative knowledge representation is required in some application domains such as food allergies, software incompatibility, and school absence. We present an approach to represent and query RDF data with negative data. We provide the syntax, semantics, and an example. We argue that this approach fits into the open-world semantics of RDF according to the notion of certain answers.

Get more information at http://dx.doi.org/10.1007/978-3-642-41242-4_40

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ESWC 2013 Poster: Representing and Querying Negative Knowledge in RDF

  1. 1. TEMPLATE DESIGN © 2007www.PosterPresentations.comRepresenting and Querying Negative Knowledge in RDFFariz DarariFree University of Bozen-Bolzano, Italyfadirra@gmail.comOverviewTypically, only positive data can be represented in RDF. However,negative knowledge representation is required in some applicationdomains such as food allergies, software incompatibility andschool absence. We present an approach to represent and queryRDF data with negative knowledge. We provide the syntax,semantics and an example. We argue that this approach fits intothe open-world semantics of RDF according to the notion ofcertain answers.Syntax• Negative RDF data are represented abstractly by:not(s, p, o)• Practical implementation by using reification with types:posStatement and :negStatement• Inconsistency occurs when:The intersection between positive and negative RDF datais not empty.• As for querying, there will be a preprocessing step to de-reify positive and negative RDF data and put them into thegraphs :posGraph and :negGraph, respectively.• SPARQL queries can contain negative triple patterns.Semantics• Simple Interpretation I of a vocabulary V is defined by (W3C):1. A non-empty set IR of resources, called the universe of I.2. A set IP, called the set of properties of I.3. A mapping IEXT from IP into the powerset IR x IR.• Semantics of positive RDF data (W3C):If E is a ground positive triple (s, p, o), then I(E) = true if s, p and oare in V, I(p) is in IP and <I(s), I(o)> is in IEXT(I(p)),otherwise I(E)= false.• Semantics of negative RDF data:If E is a ground negative triple not(s, p, o), then I(E) = true if s, pand o are in V, I(p) is in IP and <I(s), I(o)> is not in IEXT(I(p)),otherwise I(E)= false.• Semantics of SPARQL QueriesDuring evaluation, all positive triple patterns in the body of querieswill be delegated into positive graph :posGraph, whereas allnegative triple patterns will be delegated into negative graph:negGraph using GRAPH graph patterns.• TheoremFor a SPARQL query Q with positive and negative triple patternsand a consistent RDF data D, the evaluation of query Q over Dgives certain answers over all models of D.Motivating Scenario: Food AllergiesLet D be the following RDF data:{(john, eats, egg), (john, eats, nut),(tom, eats, egg), not(john, eats, fish)}Let Q be the following query:SELECT {?x} {(?x, eats, egg), not(?x, eats, fish)}Evaluating Q to D gives us: {{?x/john}}Observe that in the implementation, for example, thenegative triple not(john, eats, fish) will berepresented using reification as:_:t1:john:negStatement:eats:fish:subj:pred:objAfter dereification, the triple :john :eats :fish isstored in the graph :negGraph.The query Q during evaluation has the following form:SELECT ?x WHERE {GRAPH :posGraph {?x :eats :egg}GRAPH :negGraph {?x :eats :fish}}Future WorkWhat if:• Blank nodes were included?• RDFS schema were considered?• More expressive SPARQL queries were used?ReferenceM. Arenas, C. Gutierrez, J. Pérez, On the Semantics of SPARQL In:Semantic Web Information Management: A Model BasedPerspective, Springer, 2010 (ISBN: 978-3-642-04328-4)AcknowledgmentThe author was supported by the European Masters Program inComputational Logic (EMCL) and the project Querying IncompleteData (QUID) funded by the FU Bozen-Bolzano.

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