This report is also available as an Acrobat file.
Contents
Authoring and Design for the WWW
PRINCIPLES AND THEIR IMPLICATIONS
HTML
This information aims to give readers a deeper understanding of the strengths and
weaknesses of HTML, not instruction in its use.
Increasingly, software tools will protect authors and designers of Web
documents from needing to originate, edit or even see the HTML codes which
are at work within their documents (see Transparent HTML).
HTML, the HyperText Markup Language, is based on
SGML, the Standard Generalised Markup Language, agreed as ISO 8879.
HTML is actually defined using an SGML Document Type Declaration.
SGML was designed specifically to deliver the advantages
of functional description (described below, p29). Not all of the advantages of
this approach have actually been carried over in the way HTML is defined, even
in recent versions. If its authors had anticipated the enormous influence of
HTML arising through the explosion in use of the Web, they would probably
have defined it with greater thought for future development. HTML created the
success of the Web, but was not designed with that success in mind, most
particularly the wide range of media and forms of interaction which it is now
expected to support. Nevertheless, it provides a workable document structure
which can have other media appended to it.
Unlike the majority of file-formats, such as those for
word-processors or multimedia packages, the specification is open, published,
and can be interpreted by any browser package, of which Mosaic, Netscape and
Internet Explorer are only examples.
The purpose of HTML
HTML aims to overcome four problems which have arisen
though lack of standards. These problems have been that:
- proprietary hardware and software formats inhibit the exchange of information between one computer user and another
- fonts are essential to the display of text, but are intellectual property and cannot be given away unlicensed
- users have been prevented by the particular hardware available to them from viewing a document as its author intended (or at all)
- documents have typically been self-contained, not connected to other relevant documents (in other words, they do not have the advantages of hypertext systems)
HTML has its own answers to these problems, while
Acrobat (see Appendix Three, p104) has others.
Proprietary hardware and software formats
HTML is an evolving (informal) international standard
which aims to bypass the barriers of proprietary systems.
Fonts are property
HTML does not transmit fonts from the publisher to the
user. The fonts used are those on the user's computer. Plans are afoot to address
this problem directly, rather than side-stepping it as now (see The future p54)
Users constrained by hardware
HTML allows the content to be displayed in different ways
on differing hardware. HTML instructions which cannot be interpreted at all by
the user's computer are ignored, rather than producing an error.
Documents self-contained, unconnected
HTML offers a basic but effective system for linking any
part of a document to any part of another document, regardless of where it is
sited.
HTML allows document authors to specify:
- the structure and content of documents
- the links between component parts of a hypertext system
- the links to other media files such as pictures or animations
HTML achieves these objectives using text files containing
only ASCII characters (the basic but widely adopted standard for specifying the
alphabet, numeric digits, and some simple punctuation). ASCII character codes
are recognised by almost all the world's computers, and as such offer a means
of communication between one computer and another. Unicode, the replacement
for ASCII, will provide better support for extended character sets, but the
principle remains the same. Other, non-text, media delivered in the context of
Web pages each have their own cross-platform formats, but not all of these are
open, public formats like HTML.
Important characteristics of HTML
Layout as well as content of text files
Word processors, presentation packages and multimedia
authoring packages can all specify the layout of text and other media components,
but do so in a way which is proprietary and often uses codes which are
beyond the standard ASCII set. HTML is by it nature standardised across all
platforms (though there will always be difficulties due to new versions of
standards emerging which the available browser software then does not match).
HTML takes a relaxed attitude to where things appear on the user's screen. This
results from 1 not specifying the fonts, with all their concomitant information
about line-length, line-spacing etc and 2 not wanting to make assumptions about
the dimensions and other characteristics of the user's screen.
Links between component parts of a hypertext system
There are a number of other hypertext software systems
such as Guide, NoteCards, HyperCard etc. They use proprietary, closed means
of describing the hypertext linkages and the interactions which are offered to the
user. HTML standardises the interlinking of document components. By using
URLs, which provide a unique standardised address for every document on
every server, HTML is able to treat all HTML documents as equally accessible,
regardless of their location.
Links to other media files such as pictures or animations
Most interactive multimedia packages are able, to a greater
or lesser extent, to integrate various media components into a single surface.
HTML originally side-stepped this problem. Rather than display different media
as integrated components of a single document, HTML specified the kind of
data to be found in the file, to which the browser package responded by opening
a suitable viewer' a small self-contained package which opened up alongside
the browser to display this foreign' media type. Increasingly, browsers can
display these alternative media within the main browser window, with at least
some control over where in the window they appear.
Contents
Graphics Multimedia
Virtual Environments Visualisation
Contents
