Using Rules with Ontologies in the Semantic Web - PowerPoint PPT Presentation

1 / 15
About This Presentation
Title:

Using Rules with Ontologies in the Semantic Web

Description:

In SWRL's abstract syntax: ... DL abstracts Knowledge Representation at the expense of the reasoning mechanism. ... Complexity and Abstraction (Revisited) ... – PowerPoint PPT presentation

Number of Views:80
Avg rating:3.0/5.0
Slides: 16
Provided by: williamste
Category:

less

Transcript and Presenter's Notes

Title: Using Rules with Ontologies in the Semantic Web


1
Using Rules with Ontologies in the Semantic Web
  • Chimezie OgbujiThoracic and Cardiovascular
    SurgeryCleveland Clinic Foundation

July 25th, 2006 Presented to W3C HCLSIG ACPP Group
2
Rule Languages
  • RuleML
  • SWRL
  • Notation 3 (N3)

3
Semantic Web Reasoners
  • Closed World Machine (CWM)
  • Euler
  • Pychinko
  • RDFEngine
  • Jena

4
Using Rules to Describe Rules
  • A Rule consists of a body (antecedent) and a head
    (consequent)
  • In N3
  • ?X has ?body. ?X has ?head. body logimplies
    head gt ?X a Rule
  • In SWRLs abstract syntax
  • Implies(Antecedent(has(I-variable(X),
    I-variable(body) has(I-variable(X),
    I-variable(head)) logImplies(I-variable(body),
    I-variable(head))) Consequent(Rule(I-variable(X)))

5
Origin / Background of Rules
  • Logic Programming
  • Production systems (RETE, etc.)
  • Prolog
  • SQL
  • Horn-clause Logic
  • Efficient theorem proving, and reasoning

6
Complexity and Abstraction
  • Kurt Cagle
  • You can never eliminate complexity from a
    system, you can only move it from place to place
  • Important point regarding how / why rules are
    used with ontology languages

7
DL Semantics as Analogy for Rules
  • Description Logics (DL)
  • Strict subset of FOL with decidability in mind
  • DL are more palatable and (therefore) more
    ubiquitous
  • Ontology language constructs correspond to DL
    constructs
  • Some DL (ontology) reasoning can be done via
    explicit rules

8
Some DL Semantics as N3 Rules
  • Transitive Roles
  • ?P a owlTransitiveProperty. ?X ?P ?Y. ?Y ?P ?Z
    gt ?X ?P ?Z
  • Class inclusion
  • ?B rdfssubClassOf ?C. ?A rdfssubClassOf ?B gt
    ?A rdfssubClassOf ?C.
  • Inverse Roles
  • ?P owlinverseOf ?Q. ?S ?P ?O gt ?O ?Q ?S.
  • Functional Restrictions
  • ?P a owlFunctionalProperty. ?S ?P ?X. ?S ?P ?Y
    gt ?X owlsameAs ?Y.

9
Restriction on Expressivenes
  • Certain implications cannot be expressed in DL
  • Individuals who live and work at the same
    location are Home Workers
  • In N3
  • ?X work ?Y. ?X live ?Z. ?Z located ?W. ?Y
    located ?Y gt ?X a HomeWorker

10
Restriction on Expressiveness (Cont.)
  • Specific logical restrictions (Horn logic) make
    it difficult to express certain statements
  • Every person has a father (known or unknown)
  • However, this is straight forward in OWL (and
    Description Logics)
  • Person a owlClass
  • rdfssubClassOf
  • a owlRestriction
  • owlonProperty father
  • owlcardinality 1.

11
Rule Inference Methods
  • Given
  • Set of rules
  • Set of facts
  • Backward chaining is goal-oriented
  • Question can a fact be inferred from the rules
    and existing facts?
  • Forward chaining exhaustively infers new facts
    from the rules
  • The resulting facts combined with the original
    facts are often referred to as the closure

12
Concerns with Reasoning
  • Logic Programming reasoners and algorithms are
    more mature
  • RETE algorithm for production (forward chaining)
    systems
  • Euler cycle detection for backward chaining
    inference
  • Logic Programming systems are at the mercy of the
    explicit rules

13
Complexity and Abstraction (Revisited)
  • Kurt Cagle
  • You can never eliminate complexity from a
    system, you can only move it from place to place
  • DL abstracts Knowledge Representation at the
    expense of the reasoning mechanism.
  • DL reasoners are implemented to support only a
    limited kind of inference class subsumption and
    consistency detection.

14
Compromise
  • Use DL semantics where the domain falls nicely
    into Categories / Roles and decidability is an
    issue
  • Use rules everywhere else
  • The combination covers the full spectrum of
    expressiveness and decidability
  • Including both in the thought process improves
    Knowledge Engineering
  • Some DL semantics can be expressed as rules to
    take advantage of efficient pattern matching
    algorithms

15
References
  • Description Logic Programs Combining Logic
    Programs with Description Logic
  • http//citeseer.ist.psu.edu/grosof03description.ht
    ml
  • Description Logic Complexity Navigator
  • http//www.cs.man.ac.uk/ezolin/logic/complexity.h
    tml
  • Web Ontology Reasoning with Logic Databases
  • http//www.ubka.uni-karlsruhe.de/vvv/2004/wiwi/2/2
    .pdf
  • Eulers RDF Plus OWL N3 Rules
  • http//www.agfa.com/w3c/euler/rpo-rules.n3
  • Description Logics as Ontology Languages for the
    Semantic Web
  • http//citeseer.ist.psu.edu/baader03description.ht
    ml
Write a Comment
User Comments (0)
About PowerShow.com