The Semantic Web

1. What is the Semantic Web?
2. Where did it come from?
3. PICS, or Where has it been?
4. RDF, DAML/OIL or Where is it up to?
5. What does it do? Example - Accessibility

Charles McCN - charles@w3.org

The Semantic Web??

Using metadata to add (and extract) meaning

Part of the original design ideas of the Web

Now a W3C Activity in its own right

Let the computer do the work!

Some Key Technologies:

RDF

RDF, RDF Schema, EARL, Dublin Core, OIL, DAML

XML architecture

XML, Namespaces, XLink, Xpath, XML Schema

XML languages

XSLT, XHTML, SVG, SMIL

As well as

Annotea, CC/PP, PICS, implementation

Visions from 1994:

information that makes sense to people...

can be given semantics...

to let the computer add meaning for us.

Metadata...

What is it?

• Information about Information
• Example: Library catalogues
• To be read by a computer

  ...it has to be very simple

In Principio (of the Web)...

From HTML - IETF draft 1.2 of 1993

element link - this document links to that one

Attribute rel="X"

The link to that document is of type X

E.g. <a href="gloss" rel="glossary">xxx</a.>

xxx is linked to something that is a glossary.

rel, rev are literal text values, for documents or hypertext

old technology: PICS

level is 0, health is 9, colour is 27

often but not always gives a "minimum or maximum"

Works easily in major browsers

Includes a trust mechanism...

PICS is useful...

• Traditional uses
  • Rating for censorship
  • Local interest
  • Education level/value

Ratings bureaus allow third parties to add metadata

... but PICS is limited

name = value pairs

Hard to describe relationships

Schemes become very complex

RDF has (a bit) more power

In RDF we can...

Relate anything that can have a URI

Have literal values (for the 3rd term of a triple)

Use anonymous nodes or first-class objects

Take some information...

...and add to it

Architecture

RDF+Schema layer

• Minimalist model - (thing), Class, Property
• Subproperty, Subclass
• Domain & Range
• Comments & labels

Very wide interoperability of RDF data

"Ontology" layer

• More metainformation, such as
  • equivalence
  • Unique, Cardinality, etc
• Ontology community exists
• Huge extra usage for extra functionality

Wide interoperability & interconversion

What is Accessibility?

Making the Web useful to all people

• Multiple devices
• Sign languages
• Text-rich or text-poor
• Motion, or motion free

"Transform Gracefully"

Different input or output

CC/PP - an RDF framework for multiple devices

Equivalent alternatives, and metadata, to specify related pieces

Assistive technology to render to the users

Conversion of languages

• Part of the evolution of technology
• Version upgrade problem:

  special tricks for (e.g.) HTML tables...

• Solution: common conversion semantics

PICS helps access...

• Rate accessibility of content
  • Language level
  • Colour range
  • Document size

... but mostly for rating afterwards

More powerful: RDF

Take an SVG image that includes some RDF....

Re-render the RDF...

A beta project: text-only RDF-aware SVG browser

Cable A connects Computer A and socket 1

Cable B connects Computer B and socket 2

Cable N connects external Network and socket 5

the Hub connects socket 1 and socket 2 and socket 3 and socket 4 and socket 5

Or re-render the RDF...

Combining technologies

Some XSLT or CSS stylesheet can be used to transform Semantic content

• for a screenreader (to text)
• to make a graphic view of a table
• for braille rendering (low resolution)
• (to work in a mobile phone...)

Text is difficult too...

is a symbol for the idea surprise

is a symbol for the idea Available as a video

The theory of relativity is (available as a video) :

EARL - accessible authoring support

Evaluation And Report Language

Assesment of a particular requirement (Accessibility or not):

Examples:

• Is the text alternative actually equivalent?
• Does the document meet "508 para. (l)"?
• Has the document been approved for publication?
• Are the links and source code valid?

EARL pictured

EARL - use case (authoring)

The content team puts together a news item

• Noted they used a presupplied alternative for an image
• Claimed they meet the QuickTips requirements

Three assessment tools are used, because tool B does some bits well but not others

EARL - use case (publishing)

The sub-editors' tools check for existing reports

• check presupplied text alternatives
• edit for simpler language
• ...

Each repair is noted and need not be checked again until something changes

Thank You! Questions?

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