Ontology Development Kenneth Baclawski Northeastern University Harvard Medical School.

Ontology Development

Kenneth Baclawski

Northeastern University

Harvard Medical School

OutlineBackground on ontologiesOntology development phases

Requirements and Analysis Design and Implementation Testing and Validation Maintenance

Comparison of ontologies and software Classes Relationships Logic

Conclusion

Ontologies

Ontology: What exists in a domain and how they relate with each other.

Formal ontology: Formal treatment of the concepts and relationships in a domain.

Simple Example: Employees work for Companies Employees report to Employees

Statements

George is an employee.An object is an instance of

the Employee class.

George works for Sony.

George reports to Adam.

Fred works for a company.

Fred must report to a another employee.

Fred reports to two other employees. George says that Fred works for Toyota.

An object in the Employee class is linked with an object in the Company class

via the works_for relationship.

An object in the Employee class is linked with another object in the same class

via the reports_to relationship.

Purposes of Ontologies Basis for communication

Between people (may be informal) Between agents (formal ontologies)

Applications Representing and storing data (e.g., DB schema) Knowledge sharing within and between domains Search and retrieval Software development Classification and organization of data resources Establishing contracts Policy enforcement

Criteria for Introducing OntologiesLarge amounts of data

Data available on the Web Data acquired or generated by new techniques

Complex data structures Inheritance, containment and other hierarchies Many relationships

Diverse sources Many legacy systems Sources on the Web using different formats

Requirement for formal proofs Contracts and policy enforcement

Ontology Development TodayThe ideal is for the tools to be based on

methodologies and processes.The reality is the reverse: methodologies are

based on the tools.Opportunity: The lack of good ontology

development processes and methodologiesThesis: Given that formal ontologies are a form

of software, software development methodologies can be adapted to serve ontology development.

Classification of Ontology LanguagesLogical languages

First order predicate logic Rule based logic Description logic

Frame based languages Similar to relational databases

Graph based languages Semantic networks Analogy with the Web is rationale for the Semantic Web

Some Ontology Languages

Established languages Knowledge Interchange Format (KIF) XML Schema (XSD) Resource Description Framework (RDF) XML Topic Maps (XTM)

Emerging languages Common Logic Web Ontology Languages (OWL) Ontology Definition Metamodel (ODM)

Ontology Development Phases

Requirements and AnalysisDesign and ImplementationTesting and ValidationMaintenance

Requirements and Analysis

Least understood of all phasesDirect involvement by stakeholders is

essential, but how?Specifying the scope is important, but not all

languages support it.Point of view is also relevant.These phases offer significant opportunities

for new methodologies and processes.

Design and Implementation: Patterns and ReuseDesign pattern: Use known patternsMetaphor: Transform another ontologyComposition: Transform and combine

many smaller ontologies

Common Features

Ontology1 Ontology2

Combined Ontology

Boolean Logic

Geographic Ontology Fuzzy Logic

Fuzzy Geographic Ontology

Example of ontology composition

•The arrows are theory morphisms in the category of theories.•The composition is the colimit: the theories are combined such that the common features are equivalent.•The composition not only allows one to express fuzzy geographic statements but also to propagate uncertainty from base facts (observations) to derived facts via rules.

Design and Implementation: Refactoring

Move methods from one class to another (for example, from subclasses to superclasses).

Reification and unreification: changing relationships into classes or vice versa.

Metalevel shifting (for example, reflection)Refactoring adjusts ontological commitment.Refactoring is useful at the design,

implementation and maintenance phases.

Example of Refactoring

Example of Reification

Testing and Validation

Validation of requirements

Consistency checking

Comparison of ontologies and software

Classes Sets versus templates Behavior versus set-theory

Properties Aspects

Logic Open versus closed

Class: Set or Template

Object-oriented classes are templates. They allow one to construct objects with specified features.

Formal ontological classes are sets which can be defined in terms of other classes, attributes and associations.

Derived class example

When the age of a person is updated, membership in the Teenager class may also be changed.

When testing for membership in a class, one should use isCompatibleWith or isConsistentWith rather than instanceof.

Class: Set-theory or Behavior

Properties

Property is a general term for attributes and associations.

Are properties first class or second class?First class properties are an example of an

aspect: a feature that cuts across class boundaries.

First class properties are part of UML2.0.

Logic: Open versus Closed

Open (monotonic) logic gives different answers to queries than a closed logic.

Employee Company

10..* 10..*

works for

Suppose that Fred is just an employee: Closed world: violates constraint Open world: Fred works for a company, but

the company is not known.

Logic: Open versus Closed

Employee Company

10..* 10..*

works for

Suppose that Fred works for both Sony and IBM: Closed world: violates constraint Open world: Sony and IBM are the same

company!

StatementsFred works for a company.

The Fred object is an instance of the class of employees who work for at least one company.

Fred reports to two other employees. The Fred object is an instance of the class of

employees who report to exactly two employees. The Fred object is an instance of the class of

employees who do not report to themselves.

Statements

Fred must report to a another employee. The Fred object is an instance of the class of

employees who report to at least one employee. The Fred object is an instance of the class of

employees who do not report to themselves.

George says that Fred works for Toyota. Homework assignment. Hint: Use reification.

Conclusion

There is a noteworthy lack of methodologies and process models for ontology development.

Software development methodologies and processes could be adapted for ontologies.

However, many challenges remain to be solved.

Some of my efforts toward adapting software development for ontologies

Extend UML to support ontologies The UML has approved some of my suggestions

Direct support for ontology development by CASE tools

The OMG has issued an RFP Four initial submissions have been presented. Use cases are being developed

Transformations between formal languages The OMG has issued an RFP Six submissions are at the revised submission stage. Several products already exist