Architecture of theWorld WideWeb - Social Semantics: The Search for Meaning on the Web - page 44

Fig. 2.8 A Venn diagram
describing the relationships
between URIs, URNs, and
URLs

this standard through the IETF process years after the take-off of the Web. Indeed,
early proposals for universal names, ranging from Raymond Lull to Engelbart's
'Every Object Addressable' principle (1990), all missed the crucial advantage of
the Web; while classically names in natural language are used for reference, on the
Web names can be used to access information. In a decentralized environment this is
crucial for discovering the sense of a URI, as illustrated by the notions of 'linking'
and 'self-description' detailed next in Sects. 2.3.2 and 2.3.3 .

2.3.2 Principle of Linking

The Principle of Linking states that any resource can be linked to another resource
identified by a URI . No resource is an island, and the relationships between
resources are captured by linking, transforming lone resources into a Web. A link
is a connection between resources .The resource that the link is directed from is
called its starting resource while the resource a link is directed to is the ending
resource (DeRose et al. 2001).
What are links for? Just as URIs, links may be used for either access or reference,
or even both. In particular, in HTML the purpose of links is for access to additional
hypertext documents, and so they are sometimes called hyperlinks. This access is
often called following the link, a transversal from one Web representation to another,
that results in access to Web representations of the ending resource. A unidirectional
link that allows access of one resource from another is the predominant kind
of link in hypertext. Furthermore, access by linking is transitive, for if a user-
agent can access a Web representation of the ending resource from the starting
resource, then it can access any links present in the Web representation, and thereby
access a Web representation of an ending resource. It is precisely this ability to
transitively access documents by following links that led the original Web to be
a seamless Web of hypertext. While links can start in Web representations, the