Database Reference
In-Depth Information
A new property is defined by assigning it a URI and describing it with an
rdf:type
property whose value is the resource
rdf:Property
. For example,
we can say that “
has _ name
” is a kind of
Property
in the following way:
<rdf:Property rdf:ID = “has_name”>
<rdfs:domain rdf:resource = “mereaMaps:TopographicObject”/>
</rdf:Property>
5.6.4 s
ubpRopeRTies
, D
oMaiN
,
aND
R
aNge
RDFS also includes several properties, for example,
•
rdfs:subPropertyOf
•
rdfs:range
•
rdfs:domain
Just as classes can have subclasses, so properties can have subproperties, denoted
by
rdfs:subPropertyOf
. For example,
has _ preferred _ name
and
has _ short _ name
might be subproperties of
has _ name
. One advantage
of this is that we can differentiate between the different types of name but still
retrieve them all using the superproperty
has _ name
. If we want to state that the
subject of a particular property is always an instance of a particular class, we use
the
rdfs:range
property. Similarly, the
rdfs:domain
property allows us to
specify what class the object of the triple has to be.
<rdf:Property rdf:ID = “has_longitude”>
<rdfs:domain rdf:resource = “mereaMaps:TopographicObject”/>
<rdfs:range rdf:resource = “&xsd;float”/>
</rdf:Property>
Here, we are saying that any instance that is the object of the “
has _ longitude
”
property is of floating point type, and any instance that is the subject of the
“
has _ longitude
” property must be a
TopographicObject.
Note that this
is a far stricter statement than just saying that the
has _ longitude
property
can
be used by a
TopographicObject
, and as you can see for this example, it
is not really true: So often when authoring your RDFS ontology and modeling the
knowledge, it is best not to use domain and range unless you are absolutely sure that
these things are true and true for every instance of the class. We talk more about
knowledge modeling when we write ontologies in Chapter 10.
5.6.5 RDF C
oNTaiNeRs
aND
C
oLLeCTioNs
It is possible to denote groups of resources or values (“literals”) using one of the
RDF container constructs
rdf:Bag
(a group of resources or literals for which the
order does not matter, and duplicates are allowed);
rdf:Seq
(an ordered sequence
