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Re: Data streams and schema use and identification

• To: Dan Vint <dvint@m...>
• Subject: Re: Data streams and schema use and identification
• From: John Cowan <cowan@m...>
• Date: Wed, 23 Apr 2003 14:02:03 -0400
• Cc: xml-dev@l...
• In-reply-to: <5.2.1.1.2.20030423080053.02ee7e98@m...>
• References: <5.2.1.1.2.20030422121632.02dd81f0@p...> <5.2.1.1.2.20030422121632.02dd81f0@p...> <5.2.1.1.2.20030423080053.02ee7e98@m...>
• User-agent: Mutt/1.3.28i

Dan Vint scripsit:

> I swallowed hard on the idea of well-formed documents, but have learned 
> to live with that, but now not even being able to have a standard way to 
> determine if this XML file is supposed to be compliant with a DTD or 
> schema is almost too much to accept.

It's a different model.  An SGML or XML DTD is *logically inside* the
document (even if it's physically outside through the use of entities;
XML puts some restrictions on DTDs when physically inside, but that
doesn't affect the point), and so validation answers the question "Is
this document self-consistent?"

A WXS or RNG or Schematron schema, like an architectural meta-DTD, is
*logically outside* the document, and validation against it answers the
question "Is this document consistent with this schema?"  This entails,
of course, that there might be more than one schema with which the
document is consistent.  That being so, there can be no exclusive means
of referring to *the* schema against which a document is to be validated.

-- 
Some people open all the Windows;       John Cowan
wise wives welcome the spring           jcowan@r...
by moving the Unix.                     http://www.reutershealth.com
  --ad for Unix Book Units (U.K.)       http://www.ccil.org/~cowan
        (see http://cm.bell-labs.com/cm/cs/who/dmr/unix3image.gif)

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