Introduction to RDF and RDF Schema

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Introduction to RDFand RDF Schema

• Thomas Baker

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Tim Berners-Lee vision
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Core architectural principles

• Simple linked data model
• A has something to do with B
• A is related to B
• URIs everything has a unique identifier
• Resources described
• Metadata terms used to describe them

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URIs Everything defineduniquely on the Web
Tim Berners-Lee The most fundamental
specification of Web architecture, while one of
the simpler, is that of the Universal Resource
Identifier, or URI. The principle that anything,
absolutely anything, on the Web should be
identified distinctly is core.
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"RDF"

• Set of conventions for applications exchanging
  metadata
• Basic model for making statements about
• Resources anything named with a URI
• Description stating the properties of the
  resource using terms named by URIs
• Framework a common model (grammar) for
  statements using diverse vocabularies

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Machine-understandable

• Computers do not really understand things
• But RDF supports logical operations can process
  data so it seems they understand
• For machine-processability, statements usually
  set into XML tags
• Fundamental to RDF graph model. Other notations
  representing graphs are secondary.

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Elementary sentences

• RDF statements
• Subject what the statement is about
• Predicate property or characteristic of the
  subject
• Object part that identifies the value of the
  property

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RDF Model Primitives
Resource
Property
Value
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Simple statement in RDF
"http//doc was created by E. de Vere."
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdf"http//
www.w3.org/1999/02/22-rdf-syntax-ns" xmlnsdc"ht
tp//purl.org/dc/elements/1.1/ gt
ltrdfDescription about"http//doc gt
ltdccreatorgt Edward de Vere lt/dccreatorgt
lt/rdfDescriptiongt lt/rdfRDFgt
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Common model to integrate data

• Simple subject-predicate-object construct can
  express most of the data processed by machines
• Entries in a library catalog
• Rows in a spreadsheet
• Assertions in formal logic
• Tables in a database
• Working assumption
• More complex will not interoperate in a diverse
  Web
• Instead of asking machines to understand people's
  language, ask people to make the extra effort
  Tim Berners-Lee

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Example Description of a book
Title Antony and Cleopatra
Author Edward de Vere
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Make the subject explicit
Title Antony and Cleopatra
Book I am holding
has
has
Author Edward de Vere
Book I am holding
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Subject and predicate identifiers
dctitle Antony and Cleopatra
http//tbaker.org/book1
dccreator Edward de Vere
http//tbaker.org/book1
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Result an RDF statement
dctitle Antony and Cleopatra
http//tbaker.org/book1
dccreator Edward de Vere
http//tbaker.org/book1
Subject
Predicate
Object
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Simple statement in RDF
"http//doc was created by E. de Vere."
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdf"http//
www.w3.org/1999/02/22-rdf-syntax-ns" xmlnsdc"ht
tp//purl.org/dc/elements/1.1/ gt
ltrdfDescription about"http//doc gt
ltdccreatorgt Edward de Vere lt/dccreatorgt
lt/rdfDescriptiongt lt/rdfRDFgt
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URIs as anchors for merging data

• URIs are fixed points on global Web for
• Metadata vocabulary terms
• The resources described by those terms
• These points can be used to superimpose graphs,
  merging statements
• Creates market for aggregation, data merging,
  annotation, and filtering services

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First source
author
http//pj.org/doc/1
http//pj.org/person/pete
name
email
Pete
pete_at_pj.org
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Second source
http//pj.org/doc/1
subject
XML
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Third source
organisation
http//pj.org/person/pete
UKOLN
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Three descriptions merged
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RDF schemas define vocabularies

• RDF schemas define
• Types of things (exPerson)
• Properties (exage)
• Types of things that can serve as the subjects or
  objects of statements involving those properties
  (e.g., that exage must be an xsdinteger)

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DAMLOIL, OWL

• Beyond RDF (rdfsClass, rdftype), more words
  to characterize relations between resources
• Merger of DARPA Agent Markup Language and
  Ontology Inference Layer
• damlsameIndividualAs
• Web Ontology Language (OWL)
• owlsameClassAs
• owlcomplementOf

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Thomas.Baker_at_bi.fhg.de
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URIs anchor conceptsindependently of language
dccreator
Server in Germany
DCMI Server
Server in Jakarta