Chapter 3 A Semantic Web Primer 1 Chapter 3 Describing Web Resources in RDF Grigoris Antoniou Frank van Harmelen
Chapter 3 A Semantic Web Primer 2 Lecture Outline 1. Basic Ideas of RDF 2. XML-based Syntax of RDF 3. Basic Concepts of RDF Schema 4. Τhe Language of RDF Schema 5. The Namespaces of RDF and RDF Schema 6. Axiomatic Semantics for RDF and RDFS 7. Direct Semantics based on Inference Rules 8. Querying of RDF/RDFS Documents using SPARQL
Chapter 3 A Semantic Web Primer 3 Drawbacks of XML XML is a universal metalanguage for defining markup It provides a uniform framework for interchange of data and metadata between applications However, XML does not provide any means of talking about the semantics (meaning) of data E.g., there is no intended meaning associated with the nesting of tags – It is up to each application to interpret the nesting.
Chapter 3 A Semantic Web Primer 4 Nesting of Tags in XML David Billington is a lecturer of Discrete Maths <course name="Discrete Maths"> <lecturer>David Billington</lecturer> </course> <lecturer name="David Billington"> <teaches>Discrete Maths</teaches> </lecturer> Opposite nesting, same information!
Chapter 3 A Semantic Web Primer 5 Basic Ideas of RDF Basic building block: object-attribute-value triple – It is called a statement – Sentence about Billington is such a statement RDF has been given a syntax in XML – This syntax inherits the benefits of XML – Other syntactic representations of RDF possible
Chapter 3 A Semantic Web Primer 6 Basic Ideas of RDF (2) The fundamental concepts of RDF are: – resources – properties – statements
Chapter 3 A Semantic Web Primer 7 Resources We can think of a resource as an object, a “thing” we want to talk about – E.g. authors, books, publishers, places, people, hotels Every resource has a URI , a Universal Resource Identifier A URI can be – a URL (Web address) or – some other kind of unique identifier
Chapter 3 A Semantic Web Primer 8 Properties Properties are a special kind of resources They describe relations between resources – E.g. “written by”, “age”, “title”, etc. Properties are also identified by URIs Advantages of using URIs: – Α global, worldwide, unique naming scheme – Reduces the homonym problem of distributed data representation
Chapter 3 A Semantic Web Primer 9 Statements Statements assert the properties of resources A statement is an object-attribute-value triple – It consists of a resource, a property, and a value Values can be resources or literals – Literals are atomic values (strings)
Chapter 3 A Semantic Web Primer 10 Three Views of a Statement A triple A piece of a graph A piece of XML code Thus an RDF document can be viewed as: A set of triples A graph (semantic net) An XML document
Chapter 3 A Semantic Web Primer 11 Statements as Triples (, , #David Billington) The triple (x,P,y) can be considered as a
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- Resource Description Framework, rdf, Semantic Web Primer