Slide1

The Semantic Web

Tim Berners-Lee, Ralph Swick
http://www.w3.org/

http://www.w3.org/2000/Talks/0313-sweb-tbl

Semantic Web

A web of formulae rather than human media

Data vs documents

Weblike

• Decentralized
• Fun & unpredictable benefits of huge scale
• Compromise enable scale
• Univerality of expression: minimally constraining
• One big forumla rather than one big book

Web Architecture Reprise

• Universal Resource Identifier identifies something
• Internet protocols such as HTTP allow representation to be looked up
• Document parsed as markup
• Markup contains a URI....

First level: RDF

• Structure = DLG = unordered set of triples ("model")
• Semantics = assertions
• Vocabulary: Resources, properties.
• Concept of URI - document built in
• Can express anything using reification (cheating).
• Out-of-band definition of rdf:property semantics.

Generalizing about current KR systems

• data maps to RDF well
• inference systems use rules
• rule language deliberately limited in expressive power
• Limitation to scale: centralaized ontololgy
• Limitation to scale: fuzzy or non-monotonic reasoning
• Limitation to scale: inability to export rules

Webbing these things

• The data maps to RDF well.
• Split the rule:
  1. Classical logic assertion (export)
  2. Local processing hint (abandon)

Next Layer: Semantic Web

• Map RDF triple set into existential assertion of conjunction
• Add negation, (implication, mutually disjoint sets,...)
• Define as new property, but need syntax to avoid reification.
• Add quotation and easier syntax for quantification
• Higher order logic is inescapable.
  • Abandon completeness (being about to prove all true sentences)
  • Require consistency (not of all data, just of languge!)

SWeb processing model

There can be many, but think about reality

• Every assertion has a context
• Statement about URI
• URI dereferences to document
• Document parses to SWeLL forumula

Trusted processing

• Statement about key ...
• Document signed with key
• Document parses to Swell forumla

kassures(key, forumula) => f(statement)

The loop

Avoiding the inconsistency problem

• No system handles entire web;
• Every statement has a context
• Finding real inconsistencies is important
• Limit the type of deduction from some sources
  • assures(key,forumla)
  • shoe-assures(key,formula)
  • says(key,forumula)

Example scenarios

• Linking database columns
• Evolvability of languages
• Some problems tractable, some not

Status

• W3C members felt was a bit "researchy"
• ... but a good idea on other funding
• MIT/LCS (&...?) getting other funding
• W3C fellows, funders, etc welcome!
• W3C team tracking standards liaison

Thank you

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