1. Chapter 7: Resource Description Framework (RDF) Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005

2. Chapter 72Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns RDF Provides a basis for knowledge representation 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

3. Chapter 73Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Why RDF? XML Gives us a document tree Doesn’t identify the content represented by a document, where content means Concepts the document is about Relationships among them Enables multiple representations for the same content RDF expresses the content itself

4. Chapter 74Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Resources and Literals RDF captures descriptions of resources A resource is an “addressable” object Identified via a URI Of which a description can be given (and which is worth talking about) A literal is something simpler A value, e.g., string or integer Cannot be given a description

5. Chapter 75Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 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 Subject: a resource Object: a resource or a literal Predicate: a resource Comes with RDFS, a vocabulary to create vocabularies

6. Chapter 76Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 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 Typically abbreviated rdf and rdfs

7. Chapter 77Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Example in XML (Using Dublin Core) <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dc="http://purl.org/dc/elements/1.1/"> Service-Oriented Computing Munindar Michael Wiley rdf:Description gathers statements about one subject

8. Chapter 78Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Example in N-Triples Notation "Service-Oriented Computing". "Munindar". "Michael". "Wiley". Could also write individual statements in the XML syntax, but the rdf:Description element simplifies the notation

9. Chapter 79Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Exercise Graphs represent binary relationships naturally The vendor ships SKU-99 Express a three-party relationship The vendor ships SKU-99 quickly Hint: think of gerunds from natural language grammar

10. Chapter 710Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Reification of Statements Reify: to make referenceable, essential for quoting statements to Agree or disagree with them Assert modalities: possible, desirable, … Make a statement into a resource; then talk about it rdf:Statement is the class whose rdf:type the given statement (object) is; additional properties such as rdf:subject, rdf:object, and rdf:predicate

11. Chapter 711Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns RDF Schema Analogous to an object-oriented type system built on top of RDF. Defines 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

12. Chapter 712Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 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

13. Chapter 713Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Collections Function as containers rdf:Bag rdf:Sequence rdf:Alt (choice) Accompanied by properties to extract elements Schematically represented as rdf:_1, and so on

14. Chapter 714Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Chapter 7 Summary RDF captures deeper structure than XML RDF captures graphs in general Meaning depends on the graph, not the document that represents a graph RDF is based on an simple linguistic representation: subject, predicate, object But “webified” via URIs RDF comes with RDF Schema 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