Product Life-Cycle Metadata Modeling and Its Application with RDF
IEEE Transactions on Knowledge and Data Engineering
Integration of ontological knowledge within the authoring and retrieval of multimedia metaobjects
International Journal of Web and Grid Services
Sharing knowledge in a supply chain using the semantic web
Expert Systems with Applications: An International Journal
The three layers of adaptation granularity
UM'03 Proceedings of the 9th international conference on User modeling
Semantics and complexity of SPARQL
ISWC'06 Proceedings of the 5th international conference on The Semantic Web
EMMA – a formal basis for querying enhanced multimedia meta objects
Journal on Data Semantics IV
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To make the WWW machine-understandable there is astrong demand both for languages describing metadata andfor languages querying metadata. The Resource DescriptionFramework (RDF), a language proposed by W3C, canbe used for describing metadata about (Web) resources.RDF Schema (RDFS) extends RDF by providing meansfor creating application specific vocabularies (ontologies).While the two above languages are widely acknowledgedas a standard means for describing Web metadata, a standardizedlanguage for querying RDF metadata is still anopen issue. Research groups coming from both industry andacademia are presently involved in proposing several RDFquery languages. Due to the lack of an RDF algebra suchquery languages use APIs to describe their semantics andoptimization issues are mostly neglected. This paper proposesRAL, an RDF algebra suitable for defining (and comparing)the semantics of different RDF query languages and(at a future stage) for performing algebraic optimizations.After the definition of the data model we present the operatorsby means of which the model can be manipulated.The operators come in three flavors: extraction operatorsretrieve the needed resources from the input RDF model,loop operators support repetition, and construction operatorsbuild the resulting RDF model.