• W3C was formed in 1994 by Tim Berners-Lee
  • first "host" at MIT, Cambridge, USA
  • two more "hosts" joined later
    • INRIA, France
    • Keio University, Japan
  • there are 13 "offices" as local representations
• W3C is a member organization (around 500 members)
• W3C develops Web recommendations ("Web Standards")
  • work is done by working groups
  • working groups are staffed by members

• The current Web represents information using
  • natural language (English, Hungarian, Chinese,...)
  • graphics, multimedia, page layout
• This is okay for humans; difficult for machines!
• For distributed applications:
  • automatic procedures are involved and not (only) humans
  • agents try to make "sense" of resources on the Web
  • a well defined terminology on the domain is necessary

• A resource should provide information about itself
  • also called "metadata"
  • metadata stored in XML (or other, machine readable form)
  • metadata vocabularies should be defined
  • agents should be able to "reason" about (meta)data

  The "Semantic Web" is an infrastructure for reasoning on the Web

• It extends the current Web ("a globally linked database")

• Convey the meaning of a figure through text

  (important for accessibility)

  • add metadata to the image describing the content
  • let a tool produce some simple output using the metadata
  • use a standard metadata formalism

• The metadata is a set of statements
• In our example:
  • "the type of the full slide is a chart, and the chart type is «line»"
  • "the chart is labeled with an (SVG) text element"
  • "the legend is also a hyperlink"
  • "the target of the hyperlink is «URI»"
  • "the full slide consists of the legend, axes, and datalines"
  • "the datalines describe full and affiliate members, all members"
• The statements are about resources:
  • SVG elements, general URI-s,...

Statements can be modelled with

• Resources: an element, a URI, a literal, ...
• Properties: directed relations between two resources
• Statements: bind resources through properties
• RDF is a general model for such statements
  • can be expressed in XML or other syntaxes (eg, n3)

• You can uniquely identify all resources on the web
• Uniqueness is vital to make consistent statements
• URI-s include:
  • protocol and location dependent identifiers

    URL-s (eg, http://..., mailto:...)

  • location independent identifications

    URN-s, PURL

• Containers use special statements predefined by RDF:
  • rdf:type
  • rdf:_1, rdf:_2, rdf:_3, etc
• rdf:Bag and rdf:li are shorthands for the XML encoding
• Other types of containers are: Seq, Alt

• You should think about RDF as a labelled, undirected graph
• Full RDF of our example as a graph and in XML
• RDF is based on simple principles, but it can twist your mind...
  • one can make statements on statements, for example
• A more complicated set of statements...
  • it is not as new as you might think...

• You can use the rdf:about as a URI for external resources
• You can add RDF to XML directly (in its own namespace).

E.g, in SVG:

  <svg ...>

  ...

    <metadata>

      <rdf:RDF

        xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">

      ...

      </rdf:RDF>

    </metadata>

    ...

  </svg>

The tool:

1. Uses a public domain RDF parser to extract metadata
2. Resolves the URI-s in RDF to access the SVG elements
3. Extracts information for the output
   • eg, text element content, hyperlink data, descriptions
4. Combines this with a general text
5. Produces a (formatted) text for each RDF statement

What vocabulary should we use ("Contains", "ChartType", etc)?

• Add traditional datatypes to RDF
  • the value of the property Labelled should be a boolean

    in the mathematical sense

  • will be in the next release of RDF
• Use RDF Schemas for the basic vocabulary
  • what properties can be used?
  • what resources the properties can be applied to?

• Use an object based terminology to define resources
  • can define classes of resources
  • everything is a subclass of Resource
• Properties on resources are defined by
  • constraints on their range and domain
  • specialization (subPropertyOf)

From our example (note: it is also in RDF...):

<rdfs:Class rdf:ID="SvgEntity">

 <rdfs:comment>The class of SVG elements</rdfs:comment>

 <rdfs:subClassOf 

  rdf:resource="#http://www.w3.org/2000/01/rdf-schema#Resource"/>

</rdfs:Class>

<rdfs:Class rdf:ID="graphicsShape">

 <rdf:comment>This should be: Rectangle, Circle, ... </rdf:comment>

 <rdfs:subClassOf 

  rdf:resource="#http://www.w3.org/2000/01/rdf-schema#Literal"/>

</rdfs:Class>

<rdfs:Class rdf:ID="boolean">

 <rdfs:comment>This should be true or false</rdfs:comment>

 <rdfs:subClassOf 

  rdf:resource="#http://www.w3.org/2000/01/rdf-schema#Literal"/>

</rdfs:Class>

<rdf:Property rdf:ID="IsAnchor">

  <rdfs:domain rdf:resource="#SvgEntity"/>

  <rdfs:range rdf:resource="#boolean"/>

</rdf:Property>

<rdf:Property rdf:ID="Labelled">

  <rdfs:domain rdf:resource="#SvgEntity"/>

  <rdfs:range rdf:resource="#boolean"/>

</rdf:Property>

<rdf:Property rdf:ID="LabelledBy">

  <rdfs:subPropertyOf rdf:resource="#Labelled"/>

  <rdfs:range rdf:resource="#SvgEntity"/>

</rdf:Property>

And here is the full (RDF) schema...

RDF Schemas only offer the basic mechanism:

• no reasoning on the vocabulary elements
  • "if this property is true, then that property is also true"
  • "if this property is true, then that property is not true"
• no equivalence of terms for different vocabularies
• multiple superclasses, complex restrictions, etc, are not available

The Semantic Web needs a support to build ontologies

Goal is to develop a Web Ontologies Language:

• built on top of RDF and RDF Schemas
• based on previous works:
  • DAML (DARPA project), OIL (EU project)
  • DAML+OIL (merge of DAMN and OIL)
• practical results in logic, knowledge representation, etc

• Currently the main activity at W3C on Semantic Web
• Working Group formed in 2001
• Published the first public drafts end of July 2002

<owl:import rdf:resource="http://...."/>

<rdf:Class rdf:ID="graphicsShape">

  <owl:oneOf>

    <rdfs:Literal>Rectangle</rdfs:Literal>

    <rdfs:Literal>Circle</rdfs:Literal>

    <rdfs:Literal>Ellipse</rdfs:Literal>

    <rdfs:Literal>Polyline</rdfs:Literal>

    <rdfs:Literal>General Path</rdfs:Literal>

    <!-- etc. -->

  </owl:oneOf>

</rdf:Class>

<rdf:Class rdf:ID="animationTimeControl">

  <owl:unionOf>

    <rdf:Class rdf:resource="#AnimatePar"/>

    <rdf:Class rdf:resource="#AnimateSeq"/>

  </owl:unionOf>

</rdf:Class>

<rdf:Property rdf:ID="Link">

  <owl:unionOf>

    <rdfs:Property rdf:resource="#IsAnchor"/>

    <rdfs:Property rdf:resource="#ContainsAnchor"/>

  </owl:unionOf>

</rdf:Property>

<rdf:Property rdf:ID="NotLink">

  <owl:complementOf rdf:resource="#Link"/>

</rdf:Property>

<rdf:Property rdf:ID="isConnected">

  <owl:TransitiveProperty/>

</rdf:Property>

<rdf:Property rdf:ID="InstanceOf"/>

  <owl:FunctionalProperty/>

</rdf:Property>

<rdf:Property rdf:ID="GraphicsType">

  <owl:equivalentTo rdf:resource="http:../#TypeGraphique"/>

</rdf:Property>

RDF Primer

URI: http://www.w3.org/TR/rdf-primer

start here if you are new to RDF

RDF Syntax and Grammar

URI: http://www.w3.org/TR/rdf-syntax-grammar/

the mapping syntax to XML

Model Theory

URI: http://www.w3.org/TR/rdf-mt/

precise definition of the semantics (based on the graphs)

RDF Test Cases

URI: http://www.w3.org/TR/rdf-testcases/

RDF Schema spec.

URI: http://www.w3.org/TR/rdf-schema/

OWL Features Synopsis

URI: http://www.w3c.org/TR/owl-features/

OWL Reference

URI: http://www.w3c.org/TR/owl-ref/

OWL Abstract Syntax

URI: http://www.w3c.org/TR/owl-absyn/

Semantic Web/RDF Interest Group

a forum for discussions on applications

URI: http://www.w3.org/RDF/Interest

RDF Logic

public mailing list for detailed technical discussions

URI: http://lists.w3.org/Archives/Public/www-rdf-logic/

Annotation and Collaboration

public mailing list of RDF-based annotation systems

URI: http://lists.w3.org/Archives/Public/www-annotation/

W3C Semantic Web Home page

URI: http://www.w3.org/2001/sw/

Graphical Editors

eg, IsaViz (Xerox Research) or RDF Author (Univ. of Bristol)

RDF Environments (interpreter, etc)

HP Lab's Jena

Redland (RDF appl. framework in Python)

Validators

eg, http://www.w3.org/RDF/Validator/

Dublin Core

vocabularies for distributed Digital Libraries

one of the first metadata vocabularies in RDF

URI: http://www.dublicore.org

PRISM

(Publishing Requirements for Industry Standard Metadata)

collect, post-process, etc, content from news, catalogues, books,...

extends the Dublin Core

includes statement on digital right tracking

URI: http://www.prismstandard.org

Web Content Syndication (RSS)

can be used, eg, to analyse HTML Pages and produce news item

there is a Yahoo discussion group and (non-w3c) working group

URI: http://purl.org/rss/

example: W3C's home page reflected by Meerkat and NewsIsFree.

XMP

Adobe's tool to add RDF-based metadata to all their file formats

the tool is available for all!

URI: http://www.adobe.com/products/xmp/main.html

TAP (formerly 'The Alpiri Project')

an RDF database of 1000s of 'real world' things,

(organised into categories)

tools to turn (a domain of) the Web into a big database

URI: http://tap.standford.edu

Artiste project

An integrated art analysis and navigating environment

RDF is used to bridge the terms among several art databases

URI: http://www.artisteweb.org/index2.html

and

• How do you ensure that output #1 matches input #2?
• What does "match" means?
  • identical type (eg, using XML Schemas)?
  • subclasses of one another?
  • "equivalent" notions (eg, document <=> text file)?

Common vocabularies are necessary!

• A Web Service infrastructure needs specialized search engines
• Similar problems to the current Web... eg:
  • "see if these services can cooperate properly"
  • "find me the most efficient equation solver for my problem"
  • "how do I characterize my company's web services?"
  • etc.
• These are all "Semantic Web"-like issues:
  • managing metadata on services (ie, resources...)
  • building the right terminologies (and not only one!)
  • equivalence of various terminologies
  • logical reasoning on service descriptions

• Both developments are hosted at W3C
• The Web Services Groups also work on convergence
  • e.g., mapping of WSDL1.2 to RDF
  • cooperation with the RDF Interest Group
• The Semantic Web activity regards WS as one of its test case
• W3C participates in a European Union funded project which

  also works on this connection (SWAD)

These slides are at:

http://www.w3.org/2002/Talks/WS-HongKong-IH/

Semantic Web homepage

http://www.w3.org/2001/sw/

More information about W3C:

http://www.w3.org/Consortium/

Contact information:

http://www.w3.org/Consortium/Contact/

Mail me:

ivan@w3.org