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[Bug 29853] [FO31] fn:collation-key() does not depend on implicit-timezone

From: <bugzilla@jessica.w3.org>
Date: Wed, 21 Sep 2016 16:13:53 +0000
To: public-qt-comments@w3.org
Message-ID: <bug-29853-523-mq8oOgo0uC@http.www.w3.org/Bugs/Public/>

--- Comment #1 from Michael Kay <mike@saxonica.com> ---
Thinking about this more carefully, I think there may be a problem here. We

collation-key($K1, $C) eq collation-key($K2, $C) if and only if compare($K1,
$K2, $C) eq 0

and we also say in a note

The result of the function can be of any atomic type that permits ordering.

But what if the collation key has a type whose "eq" operator is
context-sensitive? For example, if it depends on the default collation, or on
the implicit timezone? This clearly isn't intended: the whole idea is that
collation keys should be comparable in a predictable context-free manner.

The XQuery use case we give for collation-key() 

order by fn:collation-key($e/@key, $collation)

doesn't work if the ordering semantics for collation keys are
context-dependent. To achieve this I think we need to ban the use of xs:string,
xs:untypedAtomic, and untimezoned dates/times as collation keys.

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