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DigiCULT 9
O
NTOLOGIES
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or the Semantic Web to succeed it will require
not only modelling languages, such as XML,
RDF and OWL, but it will also require methodo-
logies for extracting and defining the knowledge
that is to be represented. Decades of research and
commercial attempts to exploit the knowledge-
based systems have demonstrated the complexity of
knowledge modelling. Until there is such a metho-
dology the possibilities of XML (or any other tech-
nology) as a knowledge representation language
will not be achieved.
The success of the Semantic Web will depend
heavily upon the creation of suitable ontologies.
To avoid adding new variants to definitions we will
follow James Hendler's definition of ontology as `a
set of knowledge terms, including the vocabulary, the
semantic interconnections, and some simple rules of
inference and logic for some particular topic'
(Hendler, 2001: 30). One of the major hurdles facing
us in building the Semantic Web is the lack of suit-
able ontologies. Languages such as OWL enable
ontologies to represent `class taxonomies' and provide
mechanisms to enable their rapid development. For
example, concepts and relationships can be estab-
lished, such as `watercolour is a type of painting' or
`a necklace is a type of jewellery'. But what about
their multilingual capabilities? An ontology may well
know that a `watercolour is a painting', but it does
not necessarily mean that it knows that an `aquarelle
is a type of painting' or that a `watercolour is a type
of peinture'. In addition, and probably first we need
to consider:
| Can we cost the creation of appropriate onto-
logies for the heritage sector?
| How can we prioritise the ontologies that are
needed? (e.g. which ones should the heritage
sector develop and which ones will we be able
to borrow from other sectors?)
| What heritage-based organisations should focus
on ontology creation?
| Ontologies often fail to be interoperable.
What solutions are there to this problem and
how can they be made to work effectively?
| Does OWL (W3C's Web Ontology Semantic
Markup Language for publishing and sharing
ontologies) provide a suitable mechanism for
ontology creation for the heritage sector?
Gomez-Perez and Corcho (2002) in an analysis of
`Ontology Languages for the Semantic Web' found
that the measure of expressiveness in the current
generation of ontology creation languages is a
spectrum from XOL, RDF(S), SHOE, OML, OIL to
DAML+OIL at the richest end of the scale. Indeed
in their experience, while any of these languages will
work for very simple ontologies, any attempt to use a
weak language to create a complex ontology will fail.
Proof and trust is emerging as another central
issue. How do we know that what our agent has
discovered through its trawl of the Semantic web can
be trusted. Even in the case of ontologies how should
we decide whose ontology to trust? This is especially
important where the two ontologies may conflict
with one another. Similarly we are faced with the
difficulties of ensuring and maintaining semantic
integrity and a lack of methods for testing its
presence.
L
EGITIMISING THE
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NVESTMENT
H
eflin and Hendler (2001) make the valuable
proposal that semantic markup should be seen
as one aspect of webpage design.This in their view
would go a long way to ensuring that the costs of
this mark-up (and the underlying information
analyses that is necessary to make it happen) were
met at the appropriate stage of process of putting
material up on the web. However, Heflin and
Hendler's proposal that semantic mark-up should be
embedded into web-page design fails to recognise
that the fundamental fabric of the web is changing.
For this to happen we need a stronger argument for
the benefits that such investment will bring to the
heritage sector.
Haustein and Pleumann (2002) have noted that the
successful development of the World Wide Web
benefited from two factors: `Participation was simple,
and the results of effort were immediately visible to
the creator'. As they argue, while these two success
criteria, best classified, in my view, as ease of use and
instant gratification, were characteristic of the WWW,
they are not embedded into the fabric of the Seman-
tic Web.The Semantic Web is hard and rewards are
neither immediate nor assured.While in the long
term it may bring tremendous benefits, the near-
term take-up will be slow.
At least three other factors contributed to foster-
ing the success of the web. Firstly, the early web
developments concentrated on content creation and
not on the creation of representation languages.The
initial instantiation of HTML was simple, but it
worked and material tagged using it remained