Extending UML to Support Ontology Engineering

1
Extending UML to Support Ontology Engineering

• Kenneth Baclawski and Mieczylaw K. Kokar
• Northeastern University
• Paul A. Kogut, William S. Holmes III
• and Michael L. Aronson
• Lockheed Martin Management and Data Systems
• Lewis Hart -- GRC International
• Jeffrey Smith -- Mercury Computer
• Jerzy Letkowski -- Western New England College

2
Knowledge Representation (KR)

• Data representation language for knowledge-based
  systems
• Usually based on logic or networks (directed
  graphs)
• Usually do not rigidly separate meta levels
• Enables reasoning and semantic interoperability
  of agents at run-time
• Assumes an open rather than closed world.

3
Example of a KR
Dog
Company
Person
Vehicle
type
type
type
type
type
Toyota 853
Rover
Berizon
isOwned
George
owns
Ford 243
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Ontology

• Formal, declarative semantic model
• Data (instances) conforming to an ontology are
  called annotations.
• An ontology may include
• Vocabulary terms
• Taxonomies
• Relations
• Constraints, rules and assertions

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Example Ontology
type
ObjectProperty
Class
Person
type
Ford 243
type
type
Company
type
type
Dog
Vehicle
isOwned
subClassOf
subClassOf
type
onProperty
OwnedByAtMostOne
Toyota 853
type
type
maxCardinality
Berizon
1
Restriction
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UML as an ontology language

• UML class diagrams can define ontologies.
• Constraints such as cardinality constraints can
  be mapped to UML constructs or to OCL.
• Statecharts and Activity Diagrams are useful for
  service and process related ontologies.
• See UML for Ontology Development to appear in
  Knowledge Engineering Review

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Example Ontology in UML
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Advantages of UML for ontology

• Leverages UML tools and experience in ontology
  development.
• Provides profiles, packages and other modularity
  mechanisms currently lacking in knowledge-based
  systems.
• Supports an established mechanism for specifying
  the behavior associated with knowledge
  representations.

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Limitations of UML

• Does not (yet) have a formal semantics.
• Not Web enabled.
• Does not support properties (associations) as
  first-class model elements.

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RDF and DAML

• The Resource Description Framework (RDF) and
  DARPA Agent Markup Language (DAML) have been
  proposed as the basis for the Semantic Web.
• DAML supports semantic interoperability between
  Web pages, databases, programs and sensors by
  autonomous agents at run-time.

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Mapping UML to DAML
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Example ontology in DAML
ltClass ID"Company"/gt ltObjectProperty
ID"isOwned"gt ltinverseOfgt ltObjectProperty
ID"owns"/gt lt/inverseOfgt lt/ObjectPropertygt ltClas
s ID"Person"/gt ltRestriction ID"OwnedByAtMostOne"
gt ltmaxCardinalitygt1lt/maxCardinalitygt
ltonProperty rdfresource"isOwned"/gt lt/Restrictio
ngt ltClass ID"Vehicle"gt ltsubClassOf
rdfresource"OwnedByAtMostOne"/gt lt/Classgt ltClass
IDDog"gt ltsubClassOf rdfresource"OwnedByAtM
ostOne"/gt lt/Classgt
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First-Class Properties

• In KR languages, properties are first-class model
  elements they can be defined independently of
  any associated classes.
• UML associations must be defined in the context
  of the associated classes.
• KR properties allow one to define aspects of the
  ontology that cut across the boundaries of
  classes.

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Why not reify?

• Why not model KR properties as classes?
• It produces complex, unnatural ontologies.
• It puts the burden on the ontology developer to
  reconcile this limitation of UML.
• The resulting mapping from UML to DAML is
  unbounded (i.e., does not stabilize when applied
  repeatedly).

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MOF Specification of proposal
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Property Semantics in OCL

• A property is a grouping of Association Ends.
• Properties cross-cut Associations no property
  may have more than one Association End of an
  Association.

allConnections Set(AssociationEnd) allPropConnec
tions Set(Property) self.allConnections-gtinterse
ction(self.allPropConnectionsSet(T))Set(T) size
(T)lt1
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Conclusion

• UML is a viable language for specifying
  ontologies and knowledge representations.
• We propose a modest extension of UML to make it
  more compatible with knowledge-based systems by
  supporting first-class properties.

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Example of a KR
Company
TreeNode
Vehicle
type
type
type
type
type
Toyota 853
Node1
Berizon
isOwned
Node2
isOwned
Ford 243
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Example Ontology
ObjectProperty
Class
type
Ford 243
type
type
Company
type
type
TreeNode
Vehicle
isOwned
subClassOf
subClassOf
type
onProperty
OwnedByAtMostOne
Toyota 853
type
Berizon
type
maxCardinality
1
Restriction
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Example Ontology in UML
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Example ontology in DAML
ltClass ID"Company"/gt ltObjectProperty
ID"isOwned"gt ltinverseOfgt ltObjectProperty
ID"owns"/gt lt/inverseOfgt lt/ObjectPropertygt ltRest
riction ID"OwnedByAtMostOne"gt
ltmaxCardinalitygt1lt/maxCardinalitygt ltonProperty
rdfresource"isOwned"/gt lt/Restrictiongt ltClass
ID"Vehicle"gt ltsubClassOf rdfresource"OwnedBy
AtMostOne"/gt lt/Classgt ltClass ID"TreeNode"gt
ltsubClassOf rdfresource"OwnedByAtMostOne"/gt lt/C
lassgt