16-01-2013, 03:52 PM
RDF and RDF Schema
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XML
• Base of a family of languages and dialects.
• Marks are defined to denote the meaning of the data they
“annotate”.
• Data is self-described.
• A dialect may be defined for any domain.
• Some dialects are:
• MathML, GML, MusicXML, RSS, RDF, RDF(S)…
XML in the Semantic Web
• Data may be exchanged.
• YES.
• Semantics of published data must be
explicit.
• NO, programs can not deduce the meaning of
“marked” data from the marks.
• Properties of data and metadata may be
inferred.
• NO. Does not provide inference techniques
RDF Model
• An RDF document is a graph G that represents a set
of triples <subject, predicate, object>
• Given the following infinite sets:
• U: references to URI.
• B: Blank nodes, represents an entity that is not instantiated,
an existential variable but “actual usage does not follow this
definition”. (On Blank Nodes. Alejandro Mallea and Marcelo
Arenas and Aidan Hogan and Axel Polleres. ISWC 2011)
• L: literals
• An RDF triple (V1,V2,V3) is defined as:
• V1 corresponds to a subject and belongs to (U ∪ B)
• V2 corresponds to a predicate and belongs to U
• V3 V1 corresponds to an object and belongs to (U ∪ B ∪ L)
• A graph is ground if it does not have blank nodes.
RDF Containers
• Describe groups of things
• A book was created by several authors
• A lesson is taught by several persons
• etc.
• RDF provides a container vocabulary
• rdf:Bag. Group of resources or literals, including duplicates,
where order is not significant
• rdf:Seq. Group of resources or literals, including duplicates,
where order is significant
• rdf:Alt. Group of resources or literals tha
RDF(S)
• Language based on Frames and Semantic
Networks to define vocabularies for RDF:
• Classes of resources and properties for a specific
domain, and classes of resources where
properties may be applied.
• Taxonomies of classes and properties.
• Instances.