WebReference.com - Part 1 of chapter 1 of Cascading Style Sheets: Separating Content from Presentation, from glasshaus (2/5)
Cascading Style Sheets
Where did HTML come from?
As stated above, Berners-Lee based his new markup language on SGML, which has a wonderful history of its own.
In the late 1960's Charles Goldfarb left the legal profession to work with IBM where he established the principles of modern markup languages. His goal was to create a system that would enable the specification of documents that could be stored in a database, edited, and output for printing with a minimum of difficulty. The documents themselves were to be stored without any presentational information, containing only content and structural information.
His work, together with that of Ed Mosher and Ray Lorie,
Generalized Markup Language),
and was an ambitious effort that overcame incredible obstacles.
The task at hand was to apply his knowledge of computing to the storage, retrieval
and editing of legal documents. As he remembers it:
"That project required integrating a text editing application with an information retrieval system and a page composition program. The documents had to be kept in a repository from which they could be selected by queries. The selected documents could be revised with the text editor and returned to the database, or rendered for presentation by the composition program."
As you've learned, a markup language is used to markup, or tag, a document's elements with information regarding the elements' structural position in the document. A page header in a markup document, for example, might look like this:
<header>On the Nature of Markup</header>
However, before GML, markup (then called
procedural markup) was
application specific Â the text editor and the page composition
program of Goldfarb's project required their own unique markup to process
the documents. What GML did was to establish a uniform set of markup tags.
Documents so marked up could then be "understood" by all
the different applications needed to process the documents. The goal was platform
and application neutrality, a system whereby different applications on different
platforms could share documents freely.
SGML, the next step in the evolution of markup languages,
pushed GML even further with the introduction of
Document Type Definitions
DTDs), which allowed the creation of new
sets of markup tags for any given set of documents. A validating parser could then
read the document type definition,
which defined a specific markup system, and ensure the accuracy of the marked
up document. Applications could use the document type definition to make sense
of the document.
So what does that have to do with HTML, you ask? Well, HTML
is an SGML application, a markup language defined according to the rules of
SGML. As such, it is intended to communicate the structural meaning of HTML
document elements with a set of tags defined in the HTML document type definition.
The following is a simple example of a web page, starting with the document
type declaration (see the
") and followed by the
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" Â Â Â Â "DTD/xhtml1-transitional.dtd"> <html> Â <head> Â Â Â <title>An HTML document</title> Â </head> Â <body> Â Â Â <p>Herein is the lone content of our web page.</p> Â </body> </html>
As you can see, the content of the page is contained within a nested series of tags, which provide a structural framework for the content. The markup of the page is intended to communicate the semantic relationships of the page's elements to one another.
In this book, we'll be using
XHTML as our markup language in all
examples. XHTML is a reformulation of
the HTML vocabulary as an XML application, which is itself an SGML application.
XML was developed to sit in between HTML and SGML, retaining the simplicity
of the former while providing some of the power and flexibility of the latter.
The Web of the future will rely heavily on XML, and so the W3C has discontinued
the development of HTML, recommending instead the migration to XHTML, which
will allow documents authored today to be forward compatible with the XML
heavy Web of the future.
Created: June 10, 2002
Revised: June 10, 2002