Since Tim Berners-Lee wrote of the Semantic Web
several years ago, there has been speculation about
how we might embed meaning within Web pages, as
opposed to merely displaying content. To answer this,
XML offers the separation of content from display.
From its user definable tags, different user
communities can define their own sets of tags and
associate meaning with those. XML offers the
infrastructure. But it is still fairly low level.
Assembler language, as it were, compared to more
powerful languages like C or Java.
So if XML is like an assembler, what is the analog of
C? This book puts forward XTM, XML Topic Maps, as the
answer. It consists of 17 chapters by different
authors, outlining various aspects of XTM. The
chapters can be divided into two types.
One type has nitty gritty explanations, replete with
examples of XTM written in XML. If you are a
programmer, these chapters are for you. There are web
sites listed with XTM definitions that you can
incorporate into your XTM, just like using standard
namespaces available on the web in normal XML.
The other chapters deal with the much deeper and
harder problem of how XTM may be used for Knowledge
Organisation and Knowledge Representation. They are
high level and abstruse, edging up to the issues of
semiotics and artificial intelligence.
As a side note: In the XTM examples and
implementations given, I was surprised to see no
mention of altavista's graphical representation of
search results, circa 1998. This was not in XTM, but
it conveyed the flavour. What happened was that if you
searched for, say, 'tornado', the results would appear
as a graph. The nodes would be the main keywords in
the documents containing 'tornado'. Nodes would be
connected to each other if documents contained both
those words. In this case, one might see two non
intersecting clusters - one related to weather
patterns, and the other to jet planes. By clicking on
a node, you could expand it into finer grained graphs.
It complements this book, whose main thrust is in
manually describing XML documents in an XTM format,
because it could achieve much the same visual results,
but derived automatically from arbitrary web pages.