[OpenAjaxMobile] XML Languages

[Rotan Hanrahan]

Just to put into writing what I said about XML language design today, in
the context of assessing XACML...

 

I describe four factors to consider when designing a language that uses
XML:

 

1.       The complexity of human authoring. Will the language be written
in its raw format by a human? If so, the more complex the language, the
greater the chance of errors. Good tools and validators can help, if
they are available.

2.       The complexity of processing the XML. If it is to be consumed
by a machine, then the structure of the representations should reflect
the manner in which the data is best processed. Will it require a single
or multiple passes? Does it involve deep structures? Will the values
require exotic characters (in which case element attributes should be
avoided)? There are no hard and fast rules I can offer here, because
each use case brings its own set of challenges.

3.       Expressivity. A language that is too loose (i.e. can express a
lot) can demand much more of a processor than a language with a narrow
focus. Sometimes you only need a small amount, in which case you can
trim the fat.

4.       Human readability. Will the instances of this XML language be
read by people? If so, have you considered how the instances would be
transformed (e.g. via XSLT)? Would you be satisfied that reading the raw
XML would convey the right information to the reader?

 

There may be additional  considerations beyond the broad four above, but
my advice (based on years of floating around the XML merry-go-round in
W3C) is to keep those factors in mind when you are designing from
scratch, or evaluating a new language.

 

---Rotan

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