Date post: | 15-Apr-2017 |
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Resource Description Framework
STANLEY WANG SOLUTION ARCHITECT, TECH LEAD @SWANG68 http://www.linkedin.com/in/stanley-wang-a2b143b
• RDF is a W3C standard, which provides tool to describe Web resources provides interoperability between applications that exchange machine-
understandable information
• Composed of three basic elements Resources – the things being described Properties – the relationships between things Classes – the buckets used to group the things
Resource Description Framework
The elements are combined to make simple statements in the form of Triples:
<Subject> <Predicate> <Object>
Men In Black stars Will Smith <MenInBlack> <hasStar> <WillSmith>
Mary
Director
Secretary
to_be_in_
love_with
has_job
has_job
John
has_homepage
has_homepage
Ontology
RDF – Describe Semantic Web Resources
• Subject of an RDF statement is a resource • Predicate of an RDF statement is a property of a resource • Object of an RDF statement is the value of a property of a resource
RDF Statement
RDF Properties: type, subClassOf, subPropertyOf, range , domain, label,comment
Subject (resource) http://www.w3.org/Home/Lassila
Predicate (property) Creator
Object (literal) “Ora Lassila”
Ora Lassila is the creator of the resource http://www.w3.org/Home/Lassila.
RDF Example
Ora Lassila is the creator of the resource http://www.w3.org/Home/Lassila.
<rdf:RDF>
<rdf:Description about=
"http://www.w3.org/Home/Lassila">
<s:Creator>Ora Lassila</s:Creator>
</rdf:Description>
</rdf:RDF>
Predicate
RDF for Semantic Annotation
• RDF provides metadata about Web resources • Object -> Attribute-> Value triples • It has an XML syntax • Chained triples form a Graph
http://sepang.nottingham.edu.my/~bpayam/images/payam-barnaghi.png
has_image
#Payam payam@nottingh
am
has_email UNiM
has_teaching
http://www.nottingham.edu.my/CSIT/G53ELC
has_owner
<rdf:Description rdf:about=“#Payam”>
<has_email>payam@nottingham</has_email>
</rdf:Description>
http://sepang.nottingham.edu.my/~bpayam/#Payam
RDF Schema
• RDF Schema augments RDF to allow you to define vocabulary terms and the relations between those terms; • “extra meaning” to particular RDF predicates and
resources e.g., Class, subClassOf, Property, domain, range
• These terms are the RDF Schema building blocks (constructors) used to create vocabularies;
• RDF semantically extends RDF by providing a means to describe RDF Vocabularies;
RDF Schema is a W3C standard which defines vocabulary for RDF organizes this vocabulary in a typed hierarchy capable to explicitly
declare semantic relations between vocabulary terms
What does RDF Schema add?
• Defines vocabulary for RDF
• Organizes this vocabulary in a typed hierarchy
• class, subClassOf, type
• property, subPropertyOf
• domain, range
Alan Tom
Staff
Lecturer Research Assistant
subClassOf subClassOf
type
supervisedBy domain range
type
supervisedBy
Schema(RDFS)
Data(RDF)
Limitation of RDF
• RDF Schema is a vocabulary description language for describing properties and classes of RDF resources, with a semantics for generalization hierarchies of such properties and classes.
• RDFS is useful, but does not solve all possible requirements.
• Complex applications may want more possibilities: o similarity and/or differences of terms such as properties or classes o construct classes, not just name them o can a program reason about some terms? e.g. “if «Person» resources
«A» and «B» have the same «foaf:email» property, then «A» and «B» are identical”
This lead to the development of OWL (Web Ontology Language)