Database Reference
In-Depth Information
Web service in our example, which could only supply identifiers that were local to its
organization. When URIs are dereferenceable, they also act as a means of locating
on the Web the resource that they identify.
Let us assign the URI
http://mereamaps.gov.me/topo/0012
to the Isis Tavern pub
from our example (our resource of interest on the Web). It is not exactly snappy,
is it? Apart from taking up lots of space on the page, the longer the name is, the
higher the likelihood of introducing typographical errors, and the more long-winded
any file becomes that has to use it. To address this problem, a prefix is often used
instead of the namespace. A namespace is the scope in which the name is unique, in
this case
http://mereamaps.gov.me/topo/
.
So, we could assign the prefix “mm” to be
used instead of
http://mereamaps.gov.me/topo/
and just write the Isis Tavern's URI
as mm:0012.
Now that we have created a unique identifier for the Isis Tavern, we are ready to
move on to model some information about it in RDF.
5.4 THE RDF DATA MODEL
RDF models data as a directed graph made up of nodes (the circles) and arcs (the links
or graph “edges”), which have a direction: going out of one node and into the other node.
Figure 5.1 uses the URI we assigned to the Isis Tavern to represent its data as a
network or graph. This graph can be broken down into a number of statements made
up of a subject; a verb or verb phrase, known as a “predicate”; and an object. These
three together are often known as a “triple.” The graph of 5.1 can be written as a
number of triples, with the pub's URI as the subject of each triple. The triples that
describe the Isis Tavern pub are shown in
Table 5.2
.
mm:0012
mm:has_longitude
mm:has_latitude
mm:has_name
-1.241712
51.730031
“-e Isis
Tavern”
where mm: is the prefix representing http://mereamaps.gov.me/PlacesOfInterest/
FIGURE 5.1
The Isis Tavern represented as an RDF graph.
