rdfs:Class corresponds to the generic concept of a Type or Category,
similar to the notion of a Class in object-oriented programming languages.
When a schema defines a new class, the resource representing that class
must have an rdf:type
property whose value is the resource rdfs:Class.
Anything described by RDF expressions is called a resource and is
considered to be an instance of the class rdfs:Resource. The RDF class
rdfs:Resource represents the set called "Resources" in the formal model
for RDF presented in section 5 of the RDF Model and
Syntax specification.
rdfs:domain
indicates the classes on whose member a property can be used. (each
containing a class-expression).
If there are multiple domains, then according to DAML+OIL semantics, the
domain is the union of all domain specifications. Warning: this is
different from the semantics in RDFS.
rdfs:isDefinedBy
is a subproperty of rdfs:seeAlso
and indicates the resource defining the subject resource. Its most
common use is to identify an RDF schema that is not otherwise identified,
i.e. the URI in the resource attribute does not indicate the URI of its
schema.
rdfs:range
indicates the classes that the values of a property must be members of. If
there are multiple ranges, then according to DAML+OIL semantics, the range
is the union of all range specifications. Warning: this is different from
the semantics in RDFS.
rdfs:subClassOf
is a transitive property that specifies a subset-superset relation between
classes. Both the subject and object of the rdfs:subClassOf property must
be class-expression.
An example of a rdfs:subClassOf can represent a specialization between
classes, for instance, a ball is not only a product but one that is used
in sports.
<daml:Class rdf:ID="Ball">
<rdfs:label>Ball</rdfs:label>
<rdfs:comment>A ball designed to be in sports</rdfs:comment>
<rdfs:subClassOf rdf:resource="#Product"/>
</daml:Class>
rdfs:subPropertyOf
is an instance of rdf:Property
used to specify that one property is a specialization of another. A
property can never be declared to be a subproperty of itself, nor of any
of its own subproperties. For instance we have defined a member property,
we could then define an inactive member that is a an rdfs:subProperty of
member.
<daml:ObjectProperty rdf:ID="inactiveMember">
<rdfs:label>Inactive Member</rdfs:label>
<rdfs:comment>A member that temporarily stopped its
activity within the Club.</rdfs:comment>
<rdfs:subPropertyOf rdf:resource="#member"/>
</daml:ObjectProperty>
A daml:Class contains part of the definition of an object class. A
class refers to a class name using either rdf:about
or rdf:ID
attributes, and contains:
Instances of daml:Datatype are datatypes instead of object classes like
instances of daml:Class. A datatype is a simple type such as those defined
in the W3C XML Schema; it includes string, numbers, date, etc. The
daml:Datatype class is disjoint from the daml:Class class, therefore no
instance can be a datatype and an object class.
The
rdfs:range
value of a daml:DatatypeProperty is an instance of daml:Datatype.
An example of a daml:DatatypeProperty is the #productNumber property, its
range is a xsd:nonNegativeInteger datatype as defined in the XML Schema specification.
A
daml:List is a set of statements which recursively breaks the list down
into the first element, daml:first,
and the sublist consisting of the rest of the elements daml:rest.
When the last element is reached, the sublist of remaining elements is a
special DAML resource daml:nil.
The
rdfs:range
value of a daml:ObjectProperty is of rdf:type, daml:Class,
or any of its sub-classes. Any instance of any class, except daml:Datatype
,can be the value of the range of an instance of a daml:ObjectProperty. An
example of a daml:ObjectProperty is the #gear property, its range is a
#Product which is of rdf:type daml:Class.
