The Semantic Web - Social Semantics: The Search for Meaning on the Web - page 58

http://www.example.org/hasArchitect

http://www.example.org/GustaveEiffel

http://www.example.org/EiffelTower

http://location.example.org/hasLocation

http://www.example.org/Paris

Fig. 3.3 Merging RDF triples

Using namespaces, 2 one abbreviates the example triple to ex:EiffelTower
ex:hasArchitect ex:Gustave Eiffel . As compared to Fig. 3.1 ,the only
noticeable difference between RDF and a classical semantic network is the use
of URIs.
There are some restrictions to linking on the Semantic Web. As opposed to the
vast numbers and kinds of links possible in XLink, linking on the Semantic Web
is directed, like hyperlinks (DeRose et al. 2001). The starting resource in the triple
is called the subject , while the link itself is called the predicate ,and the ending
resource in the triple is the object . The predicate is usually a role as opposed to
an arc role. The major restriction on the Semantic Web is that the subject must be
a URI or a blank node, and the predicate must also be a URI. The object, on the
other hand, is given the most flexibility, as it may either be a URI, a blank node,
or a literal. This predicate-argument structure is a well-known and familiar structure
from logic, linguistics, and cognitive science. Triples resemble the binary predicates
in propositional logic needed to express facts, relationships, and the properties of
individuals. Furthermore, triples seem similar to simple natural language sentences,
where the subject and objects are nouns and the predicate is a verb.
From the perspective of the traditional Web, the main feature of RDF is that links
in RDF themselves have a required role URI. It is through this role that URIs are
given to relationships outside the Web in RDF. For example, the relationship of 'is
architect of' between Gustave Eiffel and the Eiffel Tower could be formalized as a
link (as shown in Fig. 3.2 ), as could the relationship between Tim Berners-Lee and
the creation of his web-page. In RDF, URIs can refer to these abstract relationships,
even if these URIs may not be accessible in the same sense as web-pages. In that
manner, RDF predicates are unlike links in traditional hypertext systems. Similarly,
a triple by itself can only state a simple assertion, but webs of links may be made
between triples to explain complex statements. A set of triples that share resources

2 So that ex=" http://www.example.org/ " .