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[Bug 5023] Relationship between identity constraints and assertions

From: <bugzilla@wiggum.w3.org>
Date: Mon, 28 Jan 2008 18:59:40 +0000
To: www-xml-schema-comments@w3.org
Message-Id: <E1JJZCm-0008Ls-Gi@wiggum.w3.org>


dret@berkeley.edu changed:

           What    |Removed                     |Added
                 CC|                            |dret@berkeley.edu

------- Comment #3 from dret@berkeley.edu  2008-01-28 18:59 -------
one thing that many people do not understand about identity constraints is that
they belong to elements and not to types and thus are not passed down the type
derivation hierarchy. so if you want an identity constraint for a type, you had
to indicate that by using a comment.

assertions now provide a way to define identity constraints which are part of
the type hierarchy, and i think this is one of the very important differences
between these constructs (and of course the expressiveness of the constraints).

in my experience with xml schema, most users have trouble understanding the
abstract type hierarchy, and how it related to the concrete elements and
attributes available for building instances. i made my initial comment because
i thought it could be very helpful for xml schema to get a better understanding
of the dependencies between certain types of constraints, and type derivation.
Received on Monday, 28 January 2008 18:59:52 UTC

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