Here we have introduced and discussed some prototypical scenarios that are on a “wish-list” for
next-generation tourism information systems. The Semantic Web that is currently investigated by
different research communities is a suitable candidate to support the development of next
-generation tourism information systems. The Semantic Web is based on machine readable and
The Syntax Layer: The interchange of data represented in the Semantic Web must
be facilitated through a concrete serialization syntax. XML is an obvious choice frequently
used by the upper layers. However, it is important to mention that the Semantic
Web is not tied to a particular syntax. Within the syntax layer Unicode is used,
that provides a unique number for every character, no matter what the platform, what
the program, or what the language is. Beside Unicode, the usage of so-called URI
(unified resource identifiers) is essential.
The RDF(S) Layer: The Semantic Web concept is to do for data what HTML did for textual
information systems: to provide sufficient flexibility to be able to represent all
databases, and logic rules to link them together to great added value. The first steps in
this direction were taken by the World-Wide Web Consortium (W3C) in defining Resource
Description Framework (RDF), a simple language for expressing relationships in triples
where any of the triple can be a first class web object. The RDF-Schema Specification,
which became a W3C candidate recommendation in March 2000, is an RDF application that
introduces an object-oriented, extensible type system to RDF. RDF-Schema is a minimalist
model, including primitives for representing classes, properties, subproperty, subclasses,
domain & range restrictions and means for representing comments & labels.
Figure 1: Semantic Web Representation Layers
The Ontology Layer: This layer includes more complex representation primitives,
such as transitive properties, cardinalities, etc.. We refer the interested reader to the
recent research initiatives OIL3 and DAML+OIL4 that are built on top of RDF(S).
E.g. OIL unifies the epistemologically rich modeling primitives of frames, the formal
semantics and efficient reasoning support of description logics and is mapped to the
standard Web metadata language proposals.
The Logical Layer: The logic layer consists of rules that enable inferences, e.g. to
choose courses of action and answer questions. The proof layer is required to provide
explanations about the answers given by automated agents that consume the provided
information. Naturally, you might want to check the results deduced by your agent,
this requires the translation of its internal reasoning mechanisms into an unifying
proof representation language.
The Proof & Trust Layer: Proof and trust mechanisms are still to be developed. At
this stage in the development of the Semantic Web, though, this problem is not tackled.
Most applications construction of a proof is done according to some fairly constrained
rules, and all that the other party has to do is validate a general proof.