Saturday, May 19, 2007

Responsibility Driven Web Design

It has been suggested as a rule of thumb that debugging and maintenance is twice as hard as writing the code in the first place -- so writing anything that is truly as clever as you can manage guarantees that you'll not be able to fix it.

Taking a responsibility led approach means that each unit that you write has a clear reason to exist, and does a well defined job. Tweaking its "mission statement" or making it adhere to it is a task that only affects the system locally -- reducing the fears that some well intentioned change will have some subtle side-effect in a distant part of the system.

But responsibility driven design is not just about organizing your objects (as I posted about here) in a conventional code library or executable. It can be a general philosophy of design.

But web design? 

Yes.  The web -- and in particular, the vast bulk of user agents (browsers) out there -- has matured greatly in recent years, and support for techniques that let us apply a separation of responsibilities approach is now almost universal.

When HTML over HTTP first emerged, it was aimed to fill a rather restricted role -- publishing scientific papers on-line, doing away with the need to mail-shot out Xeroxed pre-prints; and it filled that niche well. But then it burst out from the academic to the commercial (and hobbyist) fields. No longer were sketchily formatted grey pages with various sizes of Times Roman acceptable -- the guys from the DTP world came on-line and tried to force what had been a set of hints about layout into a pixel-perfect replica of the paper-oriented world they were familiar with.

And around the turn of the century, there was only one way to do that -- to abuse the <table> element to force a grid model into what was by its nature a fluid medium. Tables within tables within tables, propped up by 1x1 transparent spacer gifs, borders supplied by setting the background in some of the cells, became the standard -- and to be fair, with the version 3 and 4 browsers, at the height of the browser wars (remember <blink> and <marquee>? -- things seen that cannot be unseen), that was the best that could be done.

So, it worked -- after a fashion. But, to paraphrase "d00d -- where's my content?"

Updating the content of a site generated in this style was painful -- and rebranding became an exercise in starting again from scratch.

This is where separation of responsibilities comes in.

Content and how it is structured -- the semantic value of the page -- can be separated from its presentation; and the behaviour of the page separated from both of them, by using the appropriate technologies for each; respectively HTML (or XHTML) for the content, CSS for the presentation, and (unobtrusive) JavaScript for the behaviour.

Separating the presentation out into CSS gives two immediate benefits -- first, it makes you think about how the meat of your page is structured; and second, it means that you are not forcing a 600-1000 pixel wide design onto the users of small form factor devices, and can see what users of text-only browser (including text-to-speech) users will see, gaining an immediate improvement in accessibility.

To assist with moving to the non-presentational page, writing and validating pages against XHTML 1.1 is good since it has almost none of presentational tags and attributes found in HTML 4.01 (though you should be aware that there are issues regarding the RFC-compliant correct MIME-type for serving this dialect -- cutting a long story short, you should theoretically only serve it as XML, but IE can't handle that).

These days, design can be targeted at browsers with good CSS support -- Mozilla browsers from ~2003 up, Opera 8+, Safari and IE7.  Then you can fix up for IE5-6 by using IE's documented conditional comment mechanism to feed extra CSS and/or Dean Edwards' IE7 scripts to adjust to fit. Earlier browsers -- far less than 1% of the web these days -- can be protected from all this by their lack of CSS support, and get the text-only version (perhaps with colour and font styling).

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