The Resource Description Framework - Linked Data: A Geographic Perspective - page 68

TABLE 5.2
RDF Triples Describing the Isis Tavern Pub

Subject Predicate Object

http://mereamaps.gov.me/topo/0012 http://mereamaps.gov.me/topo/has_name “The Isis

Tavern”

http://mereamaps.gov.me/topo/0012 http://mereamaps.gov.me/topo/has_latitude 51.730031

http://mereamaps.gov.me/topo/0012 http://mereamaps.gov.me/topo/has_longitude -1.241712

Notice that the graph's nodes represent the subject or object of the triple, while the
graph arcs are the predicates. A subject can be a URI that represents either a specific
thing (known as an individual) such as a pub like the Isis Tavern or a class of things
such as Pub. A predicate is also sometimes called a “property” or “relationship,” and
an object is also known as a “property value.” URIs are used to name both resources
and properties. An object can be a URI for a class or individual, or it can also be just
a simple value (e.g., a string or number) that is known as a “literal,” for example, the
name “The Isis Tavern.” The literal can be plain or typed. A plain literal is a string,
which may have an optional language tag, indicating the language in which it is
written, such as English or German. A typed literal is again a string, combined with
a datatype URI to specify whether the string should be interpreted as an integer, a
floating point number, a date, or some other type. The datatype URI can be any URI,
but often a URI from the XML (eXtensible Markup Language) Schema standard is
used. In our example, the latitude and longitude could be typed literals, expressed as
floating point numbers, using “ http://www.w3.org/TR/xmlschema-2/#loat.” At the
moment, on the Web, latitude and longitude tend to be expressed as decimal, double,
or floating point numbers, using decimal degree notation, and almost never in the
traditional degrees ° minutes ′ seconds ″ format. Some data structures such as the
the Basic Geo Vocabulary (WGS84 lat/long) 2 of the World Wide Web Consortium
(W3C) simply do not bother to mention the datatype of the latitude or longitude
to “reduce the syntactic burden on RDF/XML documents,” that is, to make the
RDF shorter.
As indicated, an object can take a URI as its value that references another
resource. For example, if our user wanted to add in the extra information that the Isis
Tavern was next to the River Isis, all that the user needed to do is to add the triple as
in Table 5.3.
Note that this time, to save space, we have used the prefix “mm” for our http://
mereamaps.gov.me/topo/namespace . URIs used as predicates can be prefixed in

TABLE 5.3
RDF Triple with a Resource Object
Subject Predicate Object

mm:0012 mm:is_next_to http://sws.geonames.org/2636063