Chapter 3 Describing Web Resources in RDF Grigoris Antoniou Frank van Harmelen 1 Chapter 3 A Semantic Web Primer
1 Chapter 3 A Semantic Web Primer Chapter 3 Describing Web Resources in RDF Grigoris Antoniou Frank van Harmelen
Lecture Outline 1. Basic Ideas of rDF 2. XML-based Syntax of RDF 3. Basic Concepts of RdF Schema 4. The 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 RQL Chapter 3 A Semantic Web primer
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 RQL
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 3 Chapter 3 A Semantic Web primer
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
Nesting of Tags in XML David billington is a lecturer of Discrete Maths Discrete Maths/teaches> Lecturer Opposite nesting, same information Chapter 3 A Semantic Web primer
Chapter 3 A Semantic Web Primer 4 Nesting of Tags in XML David Billington is a lecturer of Discrete Maths David Billington Discrete Maths Opposite nesting, same information!
Basic deas of rdf e Basic building block: object-attribute-value ple 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 5 Chapter 3 A Semantic Web primer
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
Basic Ideas of RDF(2 o The fundamental concepts of rdF are resources properties statements 6 Chapter 3 A Semantic Web primer
Chapter 3 A Semantic Web Primer 6 Basic Ideas of RDF (2) ⚫ The fundamental concepts of RDF are: – resources – properties – statements
Resources e We can think of a resource as an object a thing" we want to talk about E.g. authors, books, publishers, places, people, hotels o Every resource has a uri, a Universal Resource Identifier ● A URi can be a URL (Web address)or some other kind of unique identifier 7 Chapter 3 A Semantic Web primer
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
Properties e Properties are a special kind of resources o They describe relations between resources E.g. written by, age, title, etc e Properties are also identified by Urls o Advantages of using URIs A global, worldwide, unique naming scheme Reduces the homonym problem of distributed data representation 8 Chapter 3 A Semantic Web primer
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
Statements o Statements assert the properties of resources o A statement is an object-attribute-value triple It consists of a resource, a property, and a value e Values can be resources or literals Literals are atomic values (strings) 9 Chapter 3 A Semantic Web primer
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)
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 o A graph(semantic net) ● An xml document 10 Chapter 3 A Semantic Web primer
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