RDFResource Description Framework

By: Dan Johnson & Jena Block

OutlineRDF definitionWhat is Semantic web?Search Engine ExampleWhat is RDF?TriplesVocabulariesRDF/XMLWhy RDF?

RDF

A standard for encoding metadata and other information on the Semantic Web

What is Semantic Web?•A project that aims to enable machines to do the searching, aggregating and combining of the Web's information without a human operator•An extension to the Web that adds new data and metadata to existing Web documents, extending those documents into data•An abstract intention to apply machine-exclusive meaning to the information on the web

• Documents that are not “Semantic” are in a language specific to people

• To make these documents “Semantic” we must apply a framework to the data within the document so the computer can understand it

Search Engine

Blah blah blah blah tapioca blah blah blah pudding. Chocolate pudding, blah blah blah tapioca shake. Blah blah blah blah. Blah blah blah blah tapioca pudding.

Search: “Tapioca Pudding”

SearchRestaurants Menus Desserts Sides

Search for:“Restaurants that serve Tapioca Pudding”

SearchRecipe Sites Desserts Sides

Search for:“Recipes for Tapioca Pudding”

Semantic Search Engine

Semantic search is narrower, more specific,

and more efficient

What is RDF?•Resource Description Framework•Enables the encoding, exchange and reuse of structured metadata•A general method to break down data into smaller pieces with rules of the semantics of those pieces•A way of putting web data into a context which the computer can understand

We already have ways of putting web data into a context which the computer can understand• Databases use tables• XML uses hierarchies

However, these techniques can be too restrictive

What is RDF?

The data below is too flexible to be represented by a table or hierarchy so we use a graph

To describe the data in the graph in terms that the computer can understand, we describe each relationship individually

e.g. “vincent_donofrio” “starred_in” “the_thirteenth_floor”

Triples

•RDF is a method used to break down knowledge into smaller pieces called triples•Gives rules about the semantics to these pieces•Subject, predicate, object – the subject and the object are two things in the world and the predicate is the relation between the two

my_house couchhas_a

Subject Predicate

Object

Using triple format, we can describe any series of relationships in a way that the computer can understand

e.g. “The quick brown fox jumped over the lazy dog”

Although we’ve described the relationships in the sentence, the computer still doesn’t know what these words or phrases actually mean, to solve this problem we must make a vocabulary

Subject Predicate Object

Fox is_the_speed Quick

Fox is_the_color Brown

Dog is_just Lazy

Fox jumped_over Dog

Vocabularies•Vocabulary (n) – a list of words and phrases of a language•When we create an RDF file we need to define the terms we use •We do this using a vocabulary built for the computer

Term DefinitionDog an objectFox an objectQuick a speedBrown a colorlazy an attributeis_the_speed gives a speed to an objectis_the_color gives a color to an objectis_just gives an attribute to an object

jumped_overgives the action/position relationship between two objects as one jumping over the other

We can use vocabularies that we build or we can use existing vocabularies published by someone else

Dublin Core

Property DefinitionContributor An entity responsible for making

contributions to the content of the resource

Coverage The extent or scope of the content of the resource

Creator An entity primarily responsible for making the content of the resource

Format The physical or digital manifestation of the resource

Date A date of an event in the lifecycle of the resource

Description An account of the content of the resource

RDF/XMLThe W3C specifications define an XML format to encode RDF

<?xml version="1.0"?><rdf:RDFxmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"xmlns:fd="http://www.fox_and_dog.org/">

<rdf:Description rdf:about=fd:Fox><fd:is_the_speed>"quick"</fd:is_the_speed><fd:is_the_color>"brown"</fd:is_the_color><fd:jumped_over rdf:resource=fd:Dog/>

</rdf:Description>

<rdf:Description rdf:about=fd:Dog><fd:is_just>lazy</fd:is_just>

</rdf:Description></rdf:RDF>

The RDF/XML format has the following rules:• Root element must be <RDF>• Vocabularies are referenced using XML

namespace• The RDF triples are organized using the

<Description> tag• The subject is named in the about attribute• The child nodes within the <Description> tag are

the predicates• Their content is the object

“Dog” “is_just” “Lazy”

<rdf:Description rdf:about=fd:Dog> <fd:is_just>lazy</fd:is_just>

</rdf:Description>

RDF is NOT XML!•RDF/XML is only one of many types of notation for RDF and is the only one that utilizes XML and XML namespace•The major difference between to two is in the data model

• XML is hierarchical• RDF is relational

Why RDF?•Allows multiple users the freedom of their own format while maintaining interoperability•RDF can be as descriptive as the English language while maintaining an organization that the computer can understand

However,the question of how an application will

retrieve these files has not yet been answered

Referenceshttp://www.rdfabout.com http://www.w3.org/RDF/FAQ