S Stavros Christodoulakis ACM - NTUAbikakis/papers/SPARQL-RW - Poster...S PARQL R W: Transparent...
Transcript of S Stavros Christodoulakis ACM - NTUAbikakis/papers/SPARQL-RW - Poster...S PARQL R W: Transparent...
SPARQL ̶ RW : Transparent Query Access over Mapped RDF Data Sources Kostantinos Makris 1 Nikos Bikakis 2,3 Nektarios Gioldasis 1 Stavros Christodoulakis 1
EDBT 2012 | 15th International Conference on Extending Database Technology | Berlin | Germany
Sparql
ReWritingSRW
The SPARQL2XQuery Framework
Bridging the Gab between the XML and the Semantic Web Worlds.
· XML Schema to OWL Transformation (XS2OWL plug-in)
· Mapping Specification & Generation between OWL - RDF/S and XML Schemas
· SPARQL to XQuery Query Translation
· XML ⎯ RDF Data Transformations
Family Framework
X
2
Sparql
XQuery
XS
Source Target
Motivating Example
1 Technical University of Crete, Greece 2
National Technical University of Athens, Greece
3 "Athena" Research Center, Greece
Query ReWriting
Intro
· Describes mappings between OWL/RDF-S ontology schemas· Defines and supports all the possible mapping types which can be exploited by the SPARQL query rewriting process.· The supported mappings are highly dependent to the SPARQL expressiveness.
Grammar
· Four basic notions: ‒ Class Expression ‒ Object Property Expression ‒ Datatype Property Expression ‒ Instance Expression· Expressions are defined using several operators: union (⨆), intersection (⨅), composition (○), inverse (—), domain/range restrictions, etc.· Supports N:M cardinality mappings using equivalence or subsumption relationships.
SemanticsFormal semantics based on Description Logics.
Mapping Model
The SPARQL‒RW Framework
The SPARQL-RW (SPARQL ReWriting) Framework provides a generic method for
SPARQL query rewriting, with respect to a set of predefined mappings between
ontology schemas
Key Features
· Mapping Model ‒ Specifies mapping types which can be
exploited by the SPARQL query rewriting process
‒ Formally described using Description Logics ‒ Supports Flexible & Rich Mappings
· Query Rewriting Method ‒ Based on a set of predefined mappings
between ontologies ‒ Semantics Preserving
· Java System Prototype
Architecture
Problem Definition
Let a source ontology OS, a target ontology OT
and a set of mappings M between OS and OT. Our framework takes as input a SPARQL query QS expressed over OS, and rewrites it to a semantically correspondent SPARQL query QT (expressed over OT) w.r.t. M.
Intro
Overview
· The SPARQL query rewriting process lies in the query’s graph pattern rewriting. · For each Basic Graph Pattern, rewrite each triple pattern a) by Predicate b) by Object c) by Subject.· The rewriting is independent of the query type (i.e., Select, Ask), the SPARQL solution sequence modifiers (i.e., Order By, Distinct) and the SPARQL algebra operators (i.e., Union, Optional).· Triple Patterns Types ‒ Data Triple Patterns: Deal with data and not schema info. ‒ Schema Triple Patterns: Deal with schema info. Contain RDF/RDFS/OWL terms.
Semantics Preserving Rewriting
Let DS and DT be the RDF datasets of a source and a target ontology, respectively. Similarly, let DU be the RDF dataset which is produced by merging the DS and DT datasets using a set of mappings M.
Definition (Semantics Preserving Rewriting). Let tp be a triple pattern and rp the graph pattern resulted from one step rewriting of tp w.r.t. a mapping μ M. The rewriting step performed for tp, w.r.t. the mapping μ, is semantics preserving iff the evaluation of tp and the evaluation of rp over DU, preserve the semantics of mapping μ.
In other words, let V be the common variable set between tp and rp. The relationship R (i.e., ≡, ⊑, ⊒) that holds for the mapping used in the rewriting step, should also hold between [[tp]]DU and [[rp]]DU
projected on V.
πV ([[tp]]DU) R πV ([[rp]]DU), where R { ≡, ⊑, ⊒ }
SPARQL QueriesUsing DBpedia 3.2 Vocabulary
Select ?x { ?x dbpprop-el:όνομα "Christos Papadimitriou" }
DBpedia
v. 3.7
DBLP
ACM
YAGO
IEEE
Freebase
Greek
DBpedia
DBpedia
v. 3.2
Initial TriplesRewritten Triples by
Predicate PartRewritten Triples by
Object Part
Predicate Mappings
Object Mappings
Subject Mappings Rewritten Triples by
Subject Part (Final Triples)
Mappings(RDF)
SPARQL
Qt
Qs
RDF Data
Target Ontology
SPARQL‒RW
RDF
RDF Data
Source Ontology
Mapping Type Determinator
Mapping Parser
Query Analyzer & Composer
Results VisualizerGraph Pattern Rewriter
Rewriting Rules& Axioms
FILTER Expr. Rewriter
Triple Pattern Rewriter
Triple Pattern Type Determinator
Subject Rewriter
Object Rewriter
Predicate Rewriter