Slide1
The Semantic Web
W3C MIT/LCS
WWW9 Amsterdam; 2000 May 16
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:
- Classical logic assertion (export)
- Local processing hint (abandon)
Next Layer: Semantic Web
Higher Order Logic unifies
- 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
For details of World Wide Web Consortium:
http://www.w3.org/
For slides on the web:
http://www.w3.org/2000/Talks/0516-sweb-tbl
Tim Berners-Lee, Ralph Swick
MIT-Laboratory for Computer Science; W3C Team
2000
Tim's design issus;
PCA