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Re: Schemas: Different Strokes From Different Folks

I understood Murata to have proved for RELAX NG that given two XML
languages, each (weakly) generated by a RELAX NG schema, the union _of
the languages_ would be generated by the union of the schemata.

I don't remember whether he ever used the phrase 'closed under
union' to label that property of RELAX NG. 

For this property to be true of a schema language at least two things
must be true of that _language_ before you can even ask the question:

 * There is a well-defined way to construct the union of any two
   schemata in the schema language;

 * That construction always yields a well-defined schema.

Given those, you can then set about trying to prove that (to put it in
the other direction), for any two schemata in the schema language,

  1) any 'sentence' generated by their union is generated by at
     least one of the two;

  2) no 'sentence' generated by one or the other is not generated by
     the union.

I have no idea whether this connects with what Rick asserted about

		    Henry S. Thompson, Markup Systems Ltd.
               Cavers Garden Farm, Denholm; by Hawick; TD9 8LN
                            +44 (0) 7866 471 388
	       Fax: (44) 131 651-1426, e-mail: ht@markup.co.uk
			URL: http://www.markup.co.uk/
[mail really from me _always_ has this .sig -- mail without it is forged spam]

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