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[XQuery] IBM-XQ-011: Validation and identity

From: Don Chamberlin <chamberl@almaden.ibm.com>
Date: Wed, 11 Feb 2004 15:51:34 -0800
To: public-qt-comments@w3.org
Message-ID: <OFBFC7E990.743EB017-ON88256E37.0081EB00-88256E37.0083115F@us.ibm.com>
(IBM-XQ-011) Section 3.14 (Validate Expression) states that validating a 
node destroys its identity. I believe that this issue needs more thought. 
The reason for giving a new identity to a validated node is that some of 
its contents may change (for example, default attributes may appear). But 
consider the following:

(a) The validated note has the same parent as the original node, right? 
Doesn't this mean that the content of the parent node has changed? If the 
parent node can retain its identity, why can't the validated node retain 
its identity?

(b) The working group expects to define update operators that can change 
the state of a node while preserving its identity. But presumably the 
updated node will need to be revalidated for type-safety. If validation 
destroys node identity, how can updates preserve node identity? This seems 
to violate our XQuery Requirement (3.2.5) that XQuery must be defined in a 
way that does not preclude the later introduction of update operators. 

(c) Requiring validation to generate new node identities also raises 
questions about Requirement (3.4.13) that queries must be able to preserve 
the identity of items in the Data Model.

(d) Requiring validation to generate new node identities also may place an 
unnecessary burden on implementations that perform incremental validation 
on the data model rather than serializing it and revalidating the whole 
tree from scratch.

(e) Suppose $n is bound to an element node.
Is "$n is validate{$n}" true?
Is "$n/.. is validate{$n}/.." true?
If the answers are not the same, why not?

--Don Chamberlin
Received on Wednesday, 11 February 2004 18:51:47 UTC

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