Foundations of the Semantic Web: Ontology Engineering

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Foundations of the Semantic WebOntology
Engineering

• Building Ontologies 1cDefinitions, Descriptions,
  Restrictions Axioms
• The mechanics of untangling
• Alan Rector colleagues

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The mechanics for adding necessary restrictions
depends on whether a concept is defined or
primitive

• Primitives may have necessary restrictions on the
  main frame in OilEd
• Definitions must have necessary restrictions
  expressed as separate axioms
• The transition from one to the other is a common
  operation
• New tools will make it easier, but for now it is
  a bit painful

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Describing defined concepts

• Suppose we want to say
• All professors have salary some kind of
  acceptable
• All lecturers have salary some kind of derisory
• The salary is not part of the definition of being
  a professor or lecturer
• The sufficient conditions are Person and
  academic_rank
• You dont recognise somebody as being a lecturer
  because they have a derisory salary you
  conclude that they have a derisory salary because
  they are a lecturer.
• Lecturer ? Person hasAcademicRank
  someValuesFrom Lecturer_rankLecturer ? hasSalary
  someValuesFrom Derisory
• Note the double arrow vs single arrow!
• The single arrow is expressed as an axiom
• subclass-of(Lecturer (restriction hasSalary
  someValuesFrom Derisory))
• subclass-of means implies
• Otherwise we would have to know that somebody had
  a derisory salary to recognise them as a lecturer

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To do it

• Create a functional property hasSalaryRange
• Create a ValueType SalaryRangeValueType with
  values acceptable_salary and derisory_salary
• Create a subclass axiomsubclass-of(Lecturer,
  (restriction hasSalaryRange someValuesFrom
  derisory_salary))
• Test it by creating a class probe_poor_paid?
  (restriction hasSalaryRange not acceptable_salary)

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AxiomLecturer ? hasSalaryRange someValuesFrom
derisory
Note that the axiom appears upside downin
OilEd Lecturer ? hasSalarRange
(Class hierarchy inset from viewer)
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What happens if we just add it on the main pane?
This is wrong why?
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How will Black_lecturer be classified? Why?
If you are not sure, try it, find out, and fix
itTo be correct, this probe should be
classified under lecturer. Ontology
Teaching-5b-axioms-wrong.daml
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Suppose we want to change ACS_module to a defined
class

• ACS_Module ? Module and (restriction
  ratedAs someValuesFrom ACS_rating)
• What do we have to do?

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Move current restrictions to an axiom
These move to axioms(see next slide)
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Equivalent Subclass Axiom
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Then redefine ACS_module
complete button pressed
Definition in terms of rating
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This is a common pattern as ontologies evolve

• In fact it is what we would like to encourage you
  to do
• First sketch things in as primitives
• Then define them as appropriate
• A better User Interface coming Real Soon Now.