RDF: Data Description With HTML, the Web is for reading With XML, the Web is for processing Necessary to know  who wrote this?  who owns it?  who authorised it?  when is it valid?  what rights are ascribed to it?

RDF: Metadata Data about data  information about documents title, author, journal, date, keywords  information about people role, history, salary, expertise  information about exhibits catalogue number, price, date, artist  information about metadata validity, purpose, compiler, authority

Height Width Title Artist Content: Some hills, a lake and the sun Represents: peace tranquility Blue Mountain Types of Metadata Catalogue information: artist, title, date acquired, size. Syntactic content: colour, texture and shapes. Semantic content: landscape or happiness.

Standards for Metadata What do you put in the metadata? What is the syntax? What is the semantics? Where does the metadata go?

RDF: Data Description Simple semantic network  resources  properties  values Schemas Statements Triples

RDF Model Tim Berners-Lee Author

RDF Model Tim Berners-Lee Author subject object predicate

RDF Model author Tim Berners-Lee name subject object predicate

RDF Syntax …put some metadata in here!... But RDF doesn't know about any metadata!

RDF Descriptions Someone has to invent schemes for describing things Schemas, ontologies, terminologies… External authorities Every term represented by URI  e.g.  use XML namespace to abbreviate  applies semantics and disambiguates

RDF Descriptions The title is "Trailblazing the literature" Trailblazing the literature Who defines the title? Dublin Core! XML Namespace DC= Trailblazing the literature

NB Simple RDF Example Trailblazing the literature RDF has its own namespace which is not shown here. You really need to add the following to the RDF element xmlns="

Simple RDF Example Trailblazing the literature Leslie Carr

Simple RDF Example Trailblazing the literature String Another Resource Use this RDF to get you started in the exercises!

RDF Collections The students in course are Amy, Tim, John, Mary, and Sue. RDF provides  bag  sequence  alternative

Why RDF? But why yet another standard? Any form of data can be modelled in plain XML. These slides are adapted from Tim Berners-Lee's Roadmap to the Semantic Web available at

RDF vs XML example RDF assertion  "The author of this page is Les".  triple(page, author, "Les") XMLcourseSession6.ppt#slide19 Les author

RDF vs XML How would this information be typically be represented in XML? Les or Les

RDF vs XML or href=" Les or just

RDF vs XML They all seem the same  because we understand the tags But how about these? bar bar foo

RDF vs XML Is a foo a thingy of a bar? Or bar a wotzit of a foo? There are grammatical questions we can ask of the XML structure…  e.g. does the x element contain a wotzit …but not semantic ones Because no XML semantics are defined

RDF vs XML IF a schema is defined AND IF the schema limits the number of ways of making the same statement THEN the questions  does x have a child foo with attribute a and value foo  who is the author of page MAY BE similar

RDF Schema Standard to extend RDF statements  via types, classes, inheritance  Les is the author of this book  An author is a type of person  A book is an item of merchandise Allows much richer sets of inferences

RDF Deployment Information can be "added" to items by a third party Information may be distributed  professional associations,  qualification authorities  reviewers, portal authorities Agent architecture  resolve conflicting claims

RDF Deployment Options for locating the metadata