©2003, Philippe Cudre-Mauroux, EPFL-I&C-IIF, Laboratoire de systèmes d'informations répartis LSIR...

©2003, Philippe Cudre-Mauroux, EPFL-I&C-IIF, Laboratoire de systèmes d'informations répartis

LSIR Weekly seminar

Mapping the Semantic Web


Semantic Web Road Map

• Tim Berners-Lee 1998– Basic Assertion Model

• Assertion• Quotation

– Schema Layer• Constraint expressions

– Conversion Language• Conversion from one schema to another

– Logical Layer• Deductions (inference)

• + – Digital Signature « Layer » (trust) – Query Language


5 Years Later…

• Basic Assertion Model: RDF– Resources– Properties– Statements– Containers (bag, sequence, alternative)– Higher-order statements

• Model and syntax– W3C Recommendation (1999)– Defines an abstract data model – No formal semantics!

• Implementations?

• Semantics + abstract syntax– W3C Working draft

• Others have offered formal representations…


5 Years later…

• Schema layer (RDFS)– Core classes and properties:

• Resource • Literal • XMLLiteral • Class • Property • Datatype • type • subClassOf • subPropertyOf • domain • range • label • comment

• W3C Working draft (upon completion)


5 Years later…

• Conversion language– OWL (?)

• Logical layer: Web Ontology Language (OWL)– Reference: No W3C status for the moment

• Working draft for guide

– Deliverable March 2003– Derived from DAML+OIL– Describes classes and relations between them– Phagocytes RDFS


OWL

• Classes and Individuals• Properties

– Datatypes

• Property characteristics• Property restrictions• Ontology mapping

– sameClass/PropertyAs– sameIndividualAs– differentIndividualFrom

• Complex classes– Set operator– enumerated classes– disjoint classes


XML

HTML in not enough

RDF

RDFS OWL


Query Languages: Live and Let Die


Semantic Web Deployment

• Adding RDF statements to the web• Embedded in HTML• Parallel to HTML

– TAP, TAPache (Stanford + W3C)• GetData(resource, property) => value• Search (resources)• Reflection (discovering properties)


Tomorrow will be a better day


For our eyes only

• A Web of relations is about to be built– Stable abstract data model– First examples online– Distributed in essence

• No central authority shall allocate URIs to conceptual mappings (T. Berners “W3God” Lee’s design principle)

• Distributed extensibility (cumulative knowledge)

• Right time to start to analyze it at the abstract data level


Modeling the Semantic Web (1)

• RDF statements – Eventually modeled by directed labeled graphs

• It’s all about RDF statements…– Subsequent layers may be modeled the same way

=> at the abstract data level, the whole Semantic Web is (almost…) nothing more than a distributed directed labeled graph


Modeling the Semantic Web (2)

• Graph (S,P,O) of triples (s,p,o)– subject is a URIref (URI + optional fragment id) or a blank

node (with evt. ID): s U B– predicate is a literal: p L– o U B L

• resources (r S P O) are attached to peers (I.e., web servers)– p attached directly to the peer where it is published– if s or o U then attached to the peer responsible for URI– else, s and o attached to p’s peer


Building the graph

• We need some additional info in order to build this kind of graph from one peer / resource– store all info about each incoming / outgoing edge at

every node (p2p friendly, but not web really web friendly)– central index of RDF statements: Roogle

• graphs shall be built and processed locally – impossible to maintain a global coherent graph– graphs dependent on requests

Question: how exactly should we construct this graph? (gossiping…)


First Example

PCM Bulle

Lives in

LSIR Works for

EPFL Part of lsirwww

Bulle.chEpfl.ch


Starting to work with the graph

• Create subsets of triples– transitiveness– constraints– equalities


Transitive closures

• “Enhance” the local graph with additional deducted links– transitive, symmetric, FunctionalProperty, inverseOf,

inverseFunctional, sameClassAs, samePropertyAs, sameIndividualAs, differentIndividualFrom, intersectionOf, unionOf, complementOf, oneOf, DisjointWith

– + sequence, bag, alternative – should be categorized into several groups


Transitive closures (2)

PCM Bulle

Lives in

LSIR Works for

EPFL

Union of lsirwwwBulle.chEpfl.ch

Links with “Transitive” properties

ETH domain

Swissedu.ch

Financed by

SwissConfederation.ch

Swiss Confederation

Union Of

ETHZ

Union Of

Leads

Karl Aberer

Leads

Aebischer

Questions we will have to answer: 1) given a set of statement, how many links can we infer in

general?2) how to formally define the rules to create the new links?

Mr. X Leads


Equalities

• sameClassAs, samePropertyAs, sameIndividualAs, differentIndividualFrom, intersectionOf, unionOf, complementOf, oneOf, DisjointWith

• different types of cycles are possible…• new version of S


Constraints

• Constraint properties– class, subclass, property, subproperty, type, domain,

range, ObjectProperty, DatatypeProperty, subPropertyOf, FunctionalProperty, inverseOf, inverseFunctional (P(y,x) and P(z,x) -> y = z), allValuesFrom, someValuesFrom, cardinality, hasValue, intersectionOf, unionOf, complementOf, oneOf, DisjointWith

• association rule mining S (drift from relational constraints to OWL-specific constraints!)


Constraint example

• Playing around could be fun…– ex.: well-formness of a hierarchy (a la RQL…)

• H=(N,<) a hierarchy of classes and properties• properties pi P • < shall be the smallest partial order such that if p1, p2 P

and p1 < p2, then domain(p1) domain(p2) and range(p1) range(p2)


Soooo...

Doesn’t it look exciting?What could lie ahead• definition of the graph

• mapping of “semantic gossiping” concepts

• gossiping method for browsing the graph locally• study of transitive closures• study of cycles with equalities

• shall we define new OWL primitives for translations?

• study of constraints

©2003, Philippe Cudre-Mauroux, EPFL-I&C-IIF, Laboratoire de systèmes d'informations répartis LSIR...

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