Cardinality是指属性个数约束，并不是属性值约束：
A cardinality constraint puts constraints on the number of values a property can take, in the context of this particular class description. For example, we might want to say that for a soccer team the hasPlayer property has 11 values. For a basketball team the same property would have only 5 values.
3.1.2.2 Cardinality constraints
In OWL, like in RDF, it is assumed that any instance of a class may have an arbitrary number (zero or more) of values for a particular property. To make a property required (at least one), to allow only a specific number of values for that property, or to insist that a property must not occur, cardinality constraints can be used. OWL provides three constructs for restricting the cardinality of properties locally within a class context.
NOTE: OWL Lite includes the use of all three types of cardinality constraints, but only when used with the values "0" or "1".
3.1.2.2.1 owl:maxCardinality
The cardinality constraint owl:maxCardinality is a built-in OWL property that links a restriction class to a data value belonging to the value space of the XML Schema datatype nonNegativeInteger. A restriction containing an owl:maxCardinality constraint describes a class of all individuals that have at most N semantically distinct values (individuals or data values) for the property concerned, where N is the value of the cardinality constraint. Syntactically, the cardinality constraint is represented as an RDF property element with the corresponding rdf:datatype attribute.
The following example describes a class of individuals that have at most two parents:
<owl:Restriction>
<owl:onProperty rdf:resource="#hasParent" />
<owl:maxCardinality rdf:datatype="&xsd;nonNegativeInteger">2</owl:maxCardinality>
</owl:Restriction>
RDF datatyping is discussed in more detail in Sec. 6.
3.1.2.2.2 owl:minCardinality
The cardinality constraint owl:minCardinality is a built-in OWL property that links a restriction class to a data value belonging to the value space of the XML Schema datatype nonNegativeInteger. A restriction containing an owl:minCardinality constraint describes a class of all individuals that have at least N semantically distinct values (individuals or data values) for the property concerned, where N is the value of the cardinality constraint. Syntactically, the cardinality constraint is represented as an RDF property element with the corresponding rdf:datatype attribute.
The following example describes a class of individuals that have at least two parents:
<owl:Restriction>
<owl:onProperty rdf:resource="#hasParent" />
<owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger">2</owl:minCardinality>
</owl:Restriction>
Note that an owl:minCardinality of one or more means that all instances of the class must have a value for the property.
3.1.2.2.3 owl:cardinality
The cardinality constraint owl:cardinality is a built-in OWL property that links a restriction class to a data value belonging to the range of the XML Schema datatype nonNegativeInteger. A restriction containing an owl:cardinality constraint describes a class of all individuals that have exactly N semantically distinct values (individuals or data values) for the property concerned, where N is the value of the cardinality constraint. Syntactically, the cardinality constraint is represented as an RDF property element with the corresponding rdf:datatype attribute.
This construct is in fact redundant as it can always be replaced by a pair of matching owl:minCardinality and owl:maxCardinality constraints with the same value. It is included as a convenient shorthand for the user.
The following example describes a class of individuals that have exactly two parents:
<owl:Restriction>
<owl:onProperty rdf:resource="#hasParent" />
<owl:cardinality rdf:datatype="&xsd;nonNegativeInteger">2</owl:cardinality>
</owl:Restriction>
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racer如何推理对于等于关系
