A Practical Introduction to Ontologies & OWL

Август 4, 2022

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A Practical Introduction to Ontologies & OWL

Содержание

2. Overview Elephant Traps Property Domain & Range Property Characteristics – functional properties Intersection Negation in OWL
3. Elephant Traps Common Errors in OWL generally include: Disjoint misuse – often used on defined classes
4. Property Domain & Range If a relation is: subject_individual ? hasProperty ? object_individual The domain is
5. Setting a Domain & Range Setting a domain & range on a property has global implications
6. Semantics of Domain & Range Domain and Range are not used to restrict the interface They
7. Exercise 10: IceCream and Domain
8. Trap: Property Domain Reclassification Any Class that uses a property with a domain set in an
9. Property Characteristics Inverses – if property p has inverse property q, and p links A to
10. Functional Properties An individual can only have relationships with at most one other individual along a
11. Exercise 11: Functional Properties
12. Trap: Functional Property Misuse If a property is functional and is used in several Existential restrictions
13. Intersection Classes aka “conjunction” This AND That AND TheOther This That TheOther Each class description or
14. Intersection People often ask what the difference is between using 2 existential restrictions (which are, by
15. Trap: Intersection There are 2 problems: Often we paraphrase “AND” when we logically mean “OR” The
16. ComplementOf Classes aka “Negation” “Not” Not Something ¬ Something owl:Thing A All individuals in here are
17. ComplementOf Classes Commonly used to model 3 things: A is any C that is not B
18. Exercise 12: Variations of VeggiePizza The ontology used in this example will be available at: www.co-ode.org/ontologies/brokenPizza/
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Слайд 2

Overview
Elephant Traps
Property Domain & Range
Property Characteristics – functional properties
Intersection
Negation in OWL

– ComplementOf
Class expressions test

Слайд 3

Elephant Traps
Common Errors in OWL generally include:
Disjoint misuse – often used

on defined classes by mistake
Confusing AllValueFrom and SomeValuesFrom – some doesn’t imply only, and only doesn’t imply some
Forgetting to close class descriptions
Incorrect expectations of Domain and Range defined for properties
Incorrect use of Functional Properties
Using intersection (AND) instead of union (OR), where the members of the intersection are disjoint

Слайд 4

Property Domain & Range
If a relation is: subject_individual ? hasProperty ? object_individual
The

domain is the class of the subject individual
The range is the class of the object individual (or a datatype if hasProperty is a Datatype Property)

Слайд 5

Setting a Domain & Range
Setting a domain & range on a

property has global implications
Be careful not to over-constrain your ontology
The domain & range can be set in the Properties Tab – just click Add named class(es) e.g. Setting a domain of Pizza on hasBase
Using a Universal Restriction on a Class is like setting a local range

Слайд 6

Semantics of Domain & Range
Domain and Range are not used to

restrict the interface
They are used by the reasoner to infer additional information about individuals
Any individual that uses a property with a domain set can be inferred to be a member of the domain class
the same holds for range

Слайд 7

Exercise 10: IceCream and Domain

Слайд 8

Trap: Property Domain Reclassification
Any Class that uses a property with a

domain set in an existential restriction will be inferred to be a subclass of the domain class
This is because all individuals in this class must have at least one relationship using this property – therefore, all members of this class must be members of the domain class
If these classes are disjoint with the domain then they will come out inconsistent – another reason to check all your disjoints are set
The same does not apply to range

Слайд 9

Property Characteristics
Inverses – if property p has inverse property q, and

p links A to B, then it can be inferred that q links B to A
Functional – For a given individual, the property takes only one value.
Inverse functional – The inverse of the property is functional.
Symmetric – If a property links A to B then it can be inferred that it links B to A.
Transitive – If a property links A to B and B to C then it can be inferred that it links A to C.

Слайд 10

Functional Properties
An individual can only have relationships with at most one

other individual along a functional property, e.g. if hasBase is functional this means: “Every Pizza can have at most one PizzaBase”
Description of DoubleBasePizza:
The reasoner finds this inconsistent
It looks like the interface is warning us that we can’t use the property more than once, but actually…

Слайд 11

Exercise 11: Functional Properties

Слайд 12

Trap: Functional Property Misuse
If a property is functional and is used

in several Existential restrictions on a class, the reasoner will infer that the filler classes must overlap
If any of the fillers are disjoint from each other then this cannot be the case and therefore causes an inconsistency
If they are not, no inconsistency is found!

Слайд 13

Intersection Classes
aka “conjunction”
This AND That AND TheOther
This That TheOther
Each class description

or definition is an intersection of the conditions in it
CheeseyPizza ≡ Pizza AND ∃ hasTopping CheeseTopping

Слайд 14

Intersection
People often ask what the difference is between using 2 existential

restrictions (which are, by default, in an intersection in the interface) and using a single restriction with a filler containing both the classes

Слайд 15

Trap: Intersection
There are 2 problems:
Often we paraphrase “AND” when we logically

mean “OR” The filler “CheeseTopping AND MeatTopping” cannot contain any individuals as they are disjoint, and is therefore inconsistent
If we correct this to OR, it is still wrong as we’ve got a class description that can be fulfilled by a Pizza with a single topping – either Cheese or Meat. If we had 2 existential restrictions, there would have to be at least 2 (disjoint) toppings

≠

Слайд 16

ComplementOf Classes
aka “Negation” “Not”
Not Something
¬ Something
owl:Thing
A
All individuals in here are members

of ¬A

Слайд 17

ComplementOf Classes
Commonly used to model 3 things:
A is any C that

is not B
A does not have some relation with B
A only has relations with things that are not B

Слайд 18

Exercise 12: Variations of VeggiePizza
The ontology used in this example will

be available at: www.co-ode.org/ontologies/brokenPizza/

A Practical Introduction to Ontologies &amp; OWL

Содержание

OverviewElephant TrapsProperty Domain & RangeProperty Characteristics – functional propertiesIntersectionNegation in OWL

Elephant TrapsCommon Errors in OWL generally include:Disjoint misuse – often used

Property Domain & RangeIf a relation is: subject_individual ? hasProperty ? object_individualThe

Setting a Domain & RangeSetting a domain & range on a

Semantics of Domain & RangeDomain and Range are not used to

Exercise 10: IceCream and Domain

Trap: Property Domain ReclassificationAny Class that uses a property with a

Property CharacteristicsInverses – if property p has inverse property q, and

Functional PropertiesAn individual can only have relationships with at most one

Exercise 11: Functional Properties

Trap: Functional Property MisuseIf a property is functional and is used

Intersection Classesaka “conjunction”This AND That AND TheOtherThis That TheOtherEach class description

IntersectionPeople often ask what the difference is between using 2 existential

Trap: IntersectionThere are 2 problems:Often we paraphrase “AND” when we logically

ComplementOf Classesaka “Negation” “Not”Not Something¬ Somethingowl:ThingAAll individuals in here are members

ComplementOf ClassesCommonly used to model 3 things:A is any C that

Exercise 12: Variations of VeggiePizzaThe ontology used in this example will

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