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OWL Lite: Ch. 13- Property Characteristics

OWL Lite: Ch. 13- Property Characteristics. Atilla ELÇİ. Property Characteristics. To provide additional detail info on properties beyond their declaration Metaproperties (properties of properties) and classes for general statements about properties: Global property restrictions

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OWL Lite: Ch. 13- Property Characteristics

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  1. OWL Lite: Ch. 13- Property Characteristics Atilla ELÇİ CmpE 583 Fall 2006

  2. Property Characteristics • To provide additional detail info on properties beyond their declaration • Metaproperties (properties of properties) and classes for general statements about properties: • Global property restrictions • Relating properties • Inference shortcuts • Local property restrictions CmpE 583 Fall 2006

  3. Global Property Restrictions • In order to restrict all uses of a property • These are: • Those provided by RDFS: • rdfs:domain • rdfs:range. • Functional property • Inverse functional property CmpE 583 Fall 2006

  4. Global Property Restrictions(continued) • Functional Property (owl:FunctionalProperty): • A functional property can have at most a unique value for a particular subject individual, that is, no value or one value only. <owl:ObjectProperty rdf:ID=“hasPrice”> <rdf:type rdf:resource=“&owl;FunctionalProperty/> </owl:ObjectProperty> That is, a particular item may not have a price (if the property has not been stated for it) or can have only one value for hasPrice property. • Implications: • If a reasoner finds a value for a functional property of a subject, it stops looking for more! • If a validating software (such as Prolog program testing a case question) finds more than one value, that indicates that the assertion has created an illegal condition. => Assertions are not valid! • If an individual has two items (different URIRefs) for value for a functional property, then these items are the same. CmpE 583 Fall 2006

  5. Global Property Restrictions (continued) • Inverse Functional Property (owl:InverseFunctionalProperty): • Opposite relationship of a functional property is an inverse functional property. • Identifies object properties whose values uniquely identify the subject instance of a property. <owl:ObjectProperty rdf:ID=“hasIDNumber”> <rdf:type rdf:resource=“&owl;InverseFunctionalProperty/> </owl:ObjectProperty> In typed node syntax: <owl:InverseFunctionalProperty rdf:ID=“hasIDNumber” /> That is, a value of hasIDNumber relation identifies one particular (a unique) subject. • Implications: • If a reasoner finds two URIrefs that identify resources with the same value for an OWL inverse functional property, it means that the two are referencing the same resource. • Inverse of an inverse functional property is functional! CmpE 583 Fall 2006

  6. Relating Properties • Property equivalence (owl:equivalentProperty): • Equivalent properties relate the same subject resource to the same value (object resource) where both are properties). Ex.: <owl:ObjectProperty rdf:ID=“menuPrice”> <owl:equivalentProperty rdf:resource=“#menuCost”/> </owl:ObjectProperty> where menuPrice & menuCost are equivalenced. • Subclass of owl:sameAs & rdfs:subPropertyOf property. • Good for “merging” ontologies by combining their symbol tables without actually combining the ontology documents. • Applies on any rdf:Property and returns an rdf:Property instance. CmpE 583 Fall 2006

  7. Relating Properties (continued) • Inverse Property (owl:inverseOf Property): • An inverse property relates a value (in the range) of a property back to its domain: just like the derefencing in C/C++. Ex.: <owl:ObjectProperty rdf:ID=“usedInDish”> <rdfs:comment>Means that the ingredient having this property is used in a dish</rdfs:comment> </owl:ObjectProperty> <owl:ObjectProperty rdf:ID=“hasIngredients”> <rdfs:comment>Means that the dish having this property uses an ingrediant</rdfs:comment> <owl:inverseOf rdf:resource=“#usedInDish”/> </owl:ObjectProperty> <Ingredient rdf:ID=“sugar”><rdfs:label>Refined Sugar</rdfs:label></Ingredient> <MenuItem rdf:ID=“baklava”> <rdfs:label>Turkish Baklava</rdfs:label> <hasIngredient rdf:resource=“#sugar”/> </MenuItem> • A reasoner than infers that: <Ingredient rdf:about=“#sugar”> <usedInDish rdf:resource=“#baklava”7> </Ingredient> • Note that inverseOf is symmetric! • Applies on any owl:ObjectProperty and returns an owl:ObjectProperty instance. CmpE 583 Fall 2006

  8. Inference Shortcuts • OWL statements in aid of inference engines: membership in predefined Transitive/Symmetric Object Property classes. • Transitive Property (owl:TransitiveProperty): • Means same as in math: A<B<C => A<C. <owl:TransitiveProperty rdf:ID=“smallerThan”/> <rest:Restaurant rdf:ID=“compKanteen”> <rdf:smallerThan rdf:resource=“#pizzaPizza”/></rest:Restaurant> <rest:Restaurant rdf:ID=“pizzaPizza”> <rdf:smallerThan rdf:resource=“#central”/></rest:Restaurant> This example implies that compKanteen < central. • NB: there are several restrictions on the use of transitive property in OWL Lite: • no local/global cardinality contraint on themselves, their inverses, or their superproperties; • No functional/inverse functional designation; • Domain & range must match in use (see ex above); • Applies only on owl:ObjectProperty instances. CmpE 583 Fall 2006

  9. Inference Shortcuts (continued) • Symmetric Property (owl:SymmetricProperty): • A symmetric property also relates values back to subject resources, that is, it implies a relationship in the opposite direction. <owl:SymmetricProperty rdf:ID=“goesWellWith”/> <MenuItem rdf:ID=“kadayif”> <rdfs:label>Tel Kadayif</rdfs:label> </MenuItem> <MenuItem rdf:ID=“cream”> <rdfs:label>Turkish Kaymak</rdfs:label> <goesWellWith rdf:resource=“#kadayif”/> </MenuItem> • A reasoner than infers that :kadayif :goesWellWith :cream . • NB: there are restrictions on the use of symmetric property in OWL Lite: • If the domain and range of a symmetric property are restricted, they must be the same. CmpE 583 Fall 2006

  10. Local Property Restrictions • owlRestriction: • Used to apply a property restriction to a particular class extension rather than all classes. • Can be of: • owl:onProperty • Value restriction • Cardinality restriction CmpE 583 Fall 2006

  11. Local Property Restrictions (continued) • owlRestriction / owl:onProperty: • onProperty property identifies the object property or datatype property being restricted. Another property is used to mark the specific kind of restriction. <owl:Restriction> <owl:onProperty rdf:resource= “<propertyName>”> < ... Specifics of the restriction ... /> </owl:Restriction> • The two types of local restrictions are: • Property value restriction • Property cardinality restriction. CmpE 583 Fall 2006

  12. Local Property Restrictions (continued) • Value contraints: • Used to further and individually restrict the range of a property. • The Universal quantifier: owl:allValuesFrom: <owl/Restriction> <owl:onProperty rdf:resource= “#dishFeeds”> <owl:allValuesFrom rdf:resource=“&xsd;nonNegativeInteger”/> </owl:Restriction> • The universal quantifier takes a class expression or datatype. • The Existential Quantifier: owl:someValuesFrom: • At least one value of the restricted property must be an instance of the specified class. <owl/Restriction> <owl:onProperty rdf:resource= “#sideOrder”> <owl:someValuesFrom rdf:resource=“#Salads”/> </owl:Restriction> CmpE 583 Fall 2006

  13. Local Property Restrictions (continued) Cardinality contraints: Used to restrict the number of values a property should have for subject members from a particular subject description. • The value of a cardinality constraint is restricted to 0 or 1 in OWL Lite meaning that: • 0: to prohibit the use of a property or limit the number of occurrences. • 1: to require a property or limit the number of occurrences. • Minimum cardinality (owl:minCardinality): • Example: in stating an optional item: <owl/Restriction> <owl:onProperty rdf:resource=“#hasCar”> <owl:minCardinality rdf:datatype=“&xsd;nonNegativeInteger>0</owl:minCardinality> </owl:Restriction> • Example: in stating absolute requirement of an item: <owl/Restriction> <owl:onProperty rdf:resource=“#hasTextBook”> <owl:minCardinality rdf:datatype=“&xsd;nonNegativeInteger>1</owl:minCardinality> </owl:Restriction> CmpE 583 Fall 2006

  14. Local Property Restrictions (continued) Cardinality contraints (continued) : • Maximum cardinality (owl:maxCardinality): • Example: in stating an absolute maximum of values for a class’s property: <owl/Restriction> <owl:onProperty rdf:resource= “#hasProjectPartner”> <owl:maxCardinality rdf:datatype=“&xsd;nonNegativeInteger>0</owl:maxCardinality> </owl:Restriction> • Absolute cardinality (owl:Cardinality): • May be used as shorthand for min/max cardinality. In OWL Lite only 0/1 is allowed. • For a summary of various cardinality features and purpose of use, please refer to Table 13-5 Using Appropriate Cardinality Statements and Values and Table 16.2 OWL Lite Restriction Summary CmpE 583 Fall 2006

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