XLink: A Hyperspace Oddity

In the Halcyon days of the early XML effort, just three TLAs sufficed to
map out the territory. XML itself, of course, was first born. From
there, the idea was that birth would be given to XLL (XML Linking
Language) and then XSL (eXtensible Style Language).

The theory was that just as XML resulted from subsetting SGML (ISO
8879), an XML linking language and an XML styling language would follow
from the subsetting of the HyTime (ISO/IEC 10744:1992) and DSSSL
standards (ISO/IEC 10179:1996) respectively.

Somewhere along the line -- I cannot recall where or why -- XLL changed
its name to XLink. Anyway, I wrote an article about it back in 1998 for
Dr Dobbs Journal: "XLink: The XML Linking Language". Looking back at the
article now, I would give myself ten out of ten for enthusiasm and zero
out of ten for foresight.

The introduction to the article says, "(XLink) is a draft proposal from
the World Wide Web consortium that addresses the shortcomings of HTML's
simple hypertext model and allows the rich structure of XML documents to
be fully utilized in hypertext creation and management."

Although Version 1.0 of XLink became a W3C Recommendation in June of
2001[1], it has not exactly taken the world by storm. One reason for
this is that users are remarkable tolerant of the shortcomings in the
hypertext model of HTML. Although the functionality enshrined in Xlink
looks very appealing (multi-node links, link metadata, out-of-line
linking, two way link traversal and so on.) it seems that users -- and
thus developers -- have voted with their feet and walked away.

I have a theory as to why this is so. The problem of linking things
together on the Web takes an almost vertical ascent into complexity
which layer of abstraction piling on layer of abstraction very quickly.

All you need to do is move slightly beyond the "link this to this" model
of HTML and you are in deeply complex philosophical territory. If you
doubt that this is the case, I would suggest you take a look at the
HyTime standard. The sheer size and complexity of it amply demonstrates
the enormity of problem hidden behind the simple term "linking".

Adding to the woes of XLink is the fact that there are other fields of
XML endeavor that overlap in scope with the linking problem. Perhaps
first out of the blocks was the XML namespace recommendation, which,
after much debate, eschewed the fundamental HyTime lore known as
Architectural Forms[2]. Then DTDs -- on which XLink is based -- began to
fall out of favor. Somewhere along the line the Opera web browser
shipped with a mechanism for creating links that used CSS syntax to
create links instead of XLink. Topic Maps, RDF, and the Semantic Web
addressed the linking problem from different perspectives.

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