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RE: Language Theorie concerning XML Schema (heavy, at least to me)

• To: "'Gregor'" <iamgregor@g...>,<xml-dev@l...>,<ht@i...>
• Subject: RE: Language Theorie concerning XML Schema (heavy, at least to me)
• From: "Michael Kay" <mike@s...>
• Date: Thu, 28 Apr 2005 11:14:44 +0100
• In-reply-to: <642f07b60504280307755d53e@m...>
• Thread-index: AcVL2g6ceAWNTXXnQXaim8YHNkhgcwAAF7ng

> In general, my question is: 
> Does the fact that XML Schema is a context free language with
> additional rules mean that if a parser is supporting a feature (say
> Complex Types) correctly, it will support it where ever it might
> appear nested in whatever other type? (supporting means it can
> validate an element a complexType is providing a type for, in any
> instance)
> 

I'm no theorist; but I think you are making the mistake of reading the
phrase "context free language" as if it were ordinary English. In fact, it's
a technical phrase in language theory with a technical meaning (which others
can explain far better than I can).

In particular, a schema defines the content model of each element using a
context-free grammar. But the decisions on which content model to use for
validating a particular element do depend on the position of that element
relative to other elements, which is perhaps what you were thinking of as
"context".

Michael Kay
http://www.saxonica.com/ 

• References:
  • Language Theorie concerning XML Schema (heavy, at least to me)
    • From: Gregor <iamgregor@g...>

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