Michael Kay wrote: Ø
you don't know the meaning of a piece of XML
Ø
just by looking at it;
you need to know the Ø
representation conventions What is the best way to inform users of an XML document of its representation conventions? One approach is to inform users by adding more stuff to the XML document, e.g.,
<altitude
units="feet"
reference="mean
sea level">10</altitude> But now we’ve got to inform users of the representation conventions of the new stuff.
Yikes! We’ve entered an infinite regress.
This is a problem when you are trying to communicate with aliens from another planet, but it's not really a problem when you have language in common with your users.
You teach the meaning of words by defining them in terms of things the user already knows. The explanations can be within the document or external, it doesn't really matter, but ultimately the infinite regress stops when the user correctly guesses your meaning, because you are using shared concepts to explain yourself.
Guessability is important. Users will guess that 0 means zero even if your documentation says it means 48.
And note also, there will always be some ambiguity. What does 10 feet above mean sea level mean? When was it measured, and what was the expected error in the measurement? Mean sea level where (and when)? We're talking about the real world here, and the real world is always a bit fuzzy around the edges (or around mean sea level, if you prefer).
Michael Kay Saxonica
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