Re: [xml-dev] Build Rich Complexity from a Small Set ofWell-Defined Mark

[John Cowan <cowan@mercury.ccil.org>]

Costello, Roger L. scripsit:

> Interestingly, XML Schemas is considered to be a complicated
> language. Perhaps 7 markup combinators are too many in a markup
> language?

What makes XSD complicated is the irregularity of the rules.  For example,
a choice between child elements is representable, but a choice between
attributes is not.  What is more, there are many special rules about
what can and cannot be done, the Unique Particle Attribution rule being
the most notorious.

By comparison, RELAX NG has 9 basic patterns (element, attribute,
reference, parent reference, empty, text, datatype, typed value,
notAllowed) and 8 combinator patterns (sequence, interleave, choice,
optional, zeroOrMore, oneOrMore, list, mixed), but feels much simpler
than XSD because of the relatively few restrictions in combining them.

> From that will flow complexity of great richness.

And that's just what RNG provides.

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