Dr. Jim Bowring Computer Science Department College of Charleston CSIS 690 (633) May Evening 2009 Semantic Web Principles and Practice Class 8: 8 June 2009

Class 8: Roadmap Announcements and Assignments Questions SWWO Chapter 8 SWWO Chapter 9 SWWO Chapter 12

SKOS Simple Knowledge Organization System SKOS is an area of work developing specifications and standards to support the use of knowledge organization systems (KOS) such as thesauri, classification schemes, subject heading systems and taxonomies within the framework of the Semantic Web.

FOAF The Friend of a Friend (FOAF) project is creating a Web of machine-readable pages describing people, the links between them and the things they create and do; it is a contribution to the linked information system known as the Web. FOAF defines an open, decentralized technology for connecting social Web sites, and the people they describe.Friend of a Friend

Basic OWL: Restrictions a Restriction is a Class defined by describing the individuals it contains owl:someValuesFrom “All individuals for which at least one value of the property P comes from class C” [ a owl:Restriction; owl:onProperty :playsFor; owl:someValuesFrom :AllStarTeam]

Questionnaire Example Determining if a question has been answered: q:AnsweredQuestion owl:equivalentClass [ a owl:Restriction; owl:onProperty q:hasSelectedOption owl:someValuesFrom q:Answer ]. Note: implies at least one individual (see text)

owl:allValuesFrom “the individuals for which all values of the property P come from class C.” [ a owl:Restriction; owl:onProperty P; owl:allValuesFrom C ]. Note: does NOT imply members (see text re: prerequisites)

owl:hasValue “All individuals that have the value A for the property P.” [a owl:Restriction; owl:onProperty P; owl:hasValueA ]. (see text: re: priority questions)

Modeling Practices Know what you want design, then build Inference is Key we can always query for results inference supports the consistency of the data

Modeling for reuse Insightful names vs. wishful names Name resources in CamelCase Start class names with capital letters Start property names with lowercase letters Start individual names with capital letters Name classes with singular nouns Classes vs. Individuals Test your model

Modeling Errors Rampant Classism (Antipattern) In general, linking one class to another with an object property does not support any inferences at all. There is no inference that propagates properties associated with a class to its instances, or to its subclasses, or to its super-classes. The only inferences that apply to object properties are those (see rdfs:domain and range, or owl:Restriction) that assume that the subject and object are instances, not classes.

Modeling Errors Exclusivity (antipattern) The fallacy of exclusivity is to assume that the only candidates for membership in a subclass are those things that are already known to be members of the super-class.

Modeling Errors Objectification (antipattern) A SW model does not have the same meaning and behavior as an object system, because of: AAA Open world assumption Nonunique naming

Modeling Errors Creeping Conceptualization (antipattern) KISS watch for empty classes ! design for reuse !