Chapter 7:
Resource Description
Framework (RDF)
Service-Oriented Computing: Semantics, Processes, Agents
– Munindar P. Singh and Michael N. Huhns, Wiley, 2005
RDF

Provides a basis for knowledge
representation



Chapter 7
Supports inferencing
Simple language to capture assertions
(statements), which help capture
knowledge, e.g., about resources
Combines old KR ideas (frames, OO
modeling) but uses the Web to enhance
their range and avoid some
longstanding problems
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
2
Why RDF?

XML


Gives us a document tree
Doesn’t identify the content represented by
a document, where content means




Chapter 7
Concepts the document is about
Relationships among them
Enables multiple representations for the
same content
RDF expresses the content itself
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
3
Resources and Literals


RDF captures descriptions of resources
A resource is an “addressable” object



A literal is something simpler


Chapter 7
Identified via a URI
Of which a description can be given (and
which is worth talking about)
A value, e.g., string or integer
Cannot be given a description
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
4
Statements or Triples



RDF is based on a simple grammar
An RDF document is just a set of
statements or triples
Each statement consists of




Chapter 7
Subject: a resource
Object: a resource or a literal
Predicate: a resource
Comes with RDFS, a vocabulary to
create vocabularies
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
5
Rendering RDF


RDF is not about the surface syntax but
about the underlying content
Using the XML serialization of RDF



RDF is not tied to XML
Standard XML namespace syntax
Namespaces defined by the RDF standard

Chapter 7
Typically abbreviated rdf and rdfs
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
6
Example in XML (Using Dublin Core)
<?xml version='1.0' encoding='UTF-8'?>
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:dc="http://purl.org/dc/elements/1.1/">
<rdf:Description rdf:about="http://www.wiley.com/SOC">
<dc:title>Service-Oriented Computing</dc:title>
<dc:creator>Munindar</dc:creator>
<dc:creator>Michael</dc:creator>
<dc:publisher>Wiley</dc:publisher>
</rdf:Description>
</rdf:RDF>

rdf:Description gathers statements about one subject
Chapter 7
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
7
Example in N-Triples Notation
<http://www.wiley.com/SOC>
<http://purl.org/dc/elements/1.1/title>
"Service-Oriented Computing" .
<http://www.wiley.com/SOC>
<http://purl.org/dc/elements/1.1/creator>
"Munindar" .
<http://www.wiley.com/SOC>
<http://purl.org/dc/elements/1.1/creator>
"Michael" .
<http://www.wiley.com/SOC>
<http://purl.org/dc/elements/1.1/publisher>
"Wiley" .

Could also write individual statements in the XML syntax, but the
rdf:Description element simplifies the notation
Chapter 7
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
8
Exercise

Graphs represent binary relationships
naturally


Express a three-party relationship


Chapter 7
The vendor ships SKU-99
The vendor ships SKU-99 quickly
Hint: think of gerunds from natural
language grammar
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
9
Reification of Statements

Reify: to make referenceable, essential
for quoting statements to



Make a statement into a resource; then
talk about it

Chapter 7
Agree or disagree with them
Assert modalities: possible, desirable, …
rdf:Statement is the class whose rdf:type
the given statement (object) is; additional
properties such as rdf:subject, rdf:object,
and rdf:predicate
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
10
RDF Schema

Analogous to an object-oriented type
system built on top of RDF. Defines






Chapter 7
rdfs:Class, rdfs:subClassOf
rdfs:Resource, rdfs:Literal
rdfs:Property, rdfs:subPropertyOf
rdfs:range, rdfs:domain
rdfs:label, rdfs:comment, rdfs:seeAlso
Applications of RDF Schema deferred to
OWL, which greatly enhances the above
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
11
RDF Schema versus XML Schema
Both help define custom vocabularies
 An XML Schema document gives us
syntactic details
 An RDF Schema document gives us
(part of) the meaning of a vocabulary
 An OWL document (next chapter)
captures richer meaning
Chapter 7
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
12
Collections

Function as containers




Accompanied by properties to extract
elements

Chapter 7
rdf:Bag
rdf:Sequence
rdf:Alt (choice)
Schematically represented as rdf:_1, and
so on
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
13
Chapter 7 Summary

RDF captures deeper structure than XML



RDF is based on an simple linguistic
representation: subject, predicate, object


But “webified” via URIs
RDF comes with RDF Schema



Chapter 7
RDF captures graphs in general
Meaning depends on the graph, not the document
that represents a graph
In essence, an object-oriented type system: a
vocabulary to create new vocabularies
Used for important vocabularies (FOAF, DC,
Mozilla extensions)
Provides a basis for OWL
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
14