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   Re: What are schemata

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  • From: Sean Mc grath <digitome@iol.ie>
  • To: xml-dev@ic.ac.uk
  • Date: Sun, 31 May 1998 11:13:27 +0100

>* Tim Bray
>| I kind of think that the thing people have in mind in this group
>| when they say "schema" is "expressions of syntactic constraints
>| which can be verified mechanically" or some such.
>* James K. Tauber
>| So is a schema a function that maps a document to a truth value?
[Lars Marius Garshol]
>I'd rather say that it is a definition of a set of documents, just as
>a formal language is usually considered to be the set of sentences
>that are well-formed in that language.
>The software that verifies a document could be called "a function that
>maps a document to a truth value", though. Mathematically, such
>software would perform an "element of"-test on the set of documents
>defined by the schema.
To my mind, a schema is an assertion about the structure of a unit
of data. Parsing w.r.t. to a schema both tests the veracity of the
assertion and generates a "view" of the data as an abstract
data strcture.

Any single piece of data can simultaneously be valid w.r.t. many
different schema. To test different assertions (and generate
alternate abstract data structures) parse w.r.t. a different schema.

Maybe this is what makes me uneasy about "<!DOCTYPE" in an instance.
Data binding itself to one particular schema...

Sean Mc Grath
+353 96 47391

"Me a pedant? That depends on what you mean by 'pedant'".

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