Computers & Society/World Wide Web

Prehistory of the World Wide Web
Let us begin with a brief history of the World Wide Web (WWW). Now. Of what might a prehistory of the WWW consist?

Hypertext
From the history account we learn that the concept of hypertext plays a fundamental role. But it appears that there was a not unexpected pre-history to the emergence of the hypertext. In discussing the work of John Wilkins entitled An Essay towards a Real Character and a Philosophical Language, the author Umberto Eco makes the following interesting conclusion:

«What if we regarded the defect in Wilkins' system as its prophetic virtue? What if we treated Wilkins as if he were obscurely groping towards a notion for which we have only recently invented a name — hypertext? … If this were the case, many of [Wilkins'] system's contradictions would disappear, and Wilkins could be considered as a pioneer in the idea of a flexible and multiple organization of complex data … his [project] was instead the search for ways to articulate all that natural languages permit us to say.»

The X in XML
"XML is both a boon and a threat to the web dream."

The X in XML stands for eXtensible. This signifies that XML is open. It is open in the sense that it allows growth. Note that the abbreviation is XML and not EML. There is something daring, attractive, exciting about that X. X stands for many things, depending on the culture of the society in which it appears! The two most obvious things denoted are
 * X-rated stuff: films, books... intended for adults only!
 * X-roads: where choices in direction can be made.

Since the X in XML is pronounced "ex" and may sometimes even be written that way, then we have an opportunity of charting other potential meanings. For example, to say that "she is his ex" implies something in the past. This is not the intention of the X in XML. But we can make it so. We can think of XML poetically as X-ML to refer to the SGML that preceded it.

And we can use exactly the same interpretation for XHTML.

Xwords & partial understanding
We want to understand exactly how the XML-speaking machines influence the development of our societies. And yes! there is more than one society in the world. And yes! XML is language for the machines. "XML namespaces will allow documents to work in a mixture of globally standard terms and locally agreed-upon terms. The inference languages will allow computer to translate not all of a document, but enough of it to be able to act on it. Operating on such 'partial understanding' is fundamental, and we do it all the time in the nonelectronic world."

If you want to learn the technical details of XML then why not open the Wikibook on XML and start right away?

The X in Xword (or X-word) is usually taken to mean crossword (cross-word). But we will introduce the X meaning of XML and talk about extensible words. For example, "dossier" is a word which names a special kind of document. The bracketing pair ... is an Xword which extends "dossier". How does it extend dossier? Well, by filling in its meaning as structure, the structure of the document.

XLink
An XLink is a link belonging to the XML-world (or simply just the X-world). In other words an XLink is an "extensible" link. We can extend the concept and, hence the digital reality, as much as we can imagine. Much of the imagination is often dampened down by the technologies available, especially in general WWW use. It is important to recall, that XLink almost feels like "ancient history" in 2008. It precedes the arrival of Facebook (2004), Flickr (2004), YouTube (2005), and so on.

A good technical overview of XLink is available on Wikipedia.

But actual applications based on XLink are very few. Why is that? One major reason is undoubtedly the subsequent emergence of the Resource Description Framework (RDF). In the abstract, the essential component of RDF, called a triple, is simply represented by a directed arrow of the form • → • which connects something on the left (denoted abstractly by ‘•’) to something on the right (also abstractly by ‘•’). For example, the saying "faraway hills are green" is a simple statement connecting hills and the color green. In the arrow form, we might write "faraway hills" → "green" where the directed arrow is to be labelled with something like "hasColor". Sometimes the saying may be presented as "far away hills are green" where "faraway" is written as two separate words "far" and "away". Because of the focus or intent, the same triple would be used. And in the context of speech, rather than writing, there is no distinction between "faraway" and "far away". This remark is significant for the full richness of media in the WWW.

An XLink • → • is not a mere triple in the RDF sense. It is much much more.

XLink kinds
There are only two kinds of XLink: Although they are closely related conceptually, the simple-link is syntactically very different from the extended XLink. "Simple links offer shorthand syntax for a common kind of link, an outbound link with exactly two participating resources (into which category HTML-style A and IMG links fall). Because simple links offer less functionality than extended links, they have no special internal structure."
 * simple XLink
 * extended XLink

From this formal text we may deduce that the simple link has exactly the form • → • and it is an "outbound" link.

XForms
A good technical overview of Xforms is available on Wikipedia. Then if you wish to get into more detail, why not try out the XForms Wikibook?

Reading links
  

e-Links
There is a beautiful Wikibook on XML. Tim Berners-Lee: Weaving the Web. 