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[Bug 6228] is float a restriction of double?

From: <bugzilla@wiggum.w3.org>
Date: Fri, 14 Nov 2008 18:45:26 +0000
To: www-xml-schema-comments@w3.org
Message-Id: <E1L13fa-0006fF-Tw@farnsworth.w3.org>

http://www.w3.org/Bugs/Public/show_bug.cgi?id=6228





--- Comment #3 from Michael Kay <mike@saxonica.com>  2008-11-14 18:45:26 ---
>Amusing aside:  unsignedByte is not derived from short, but I believe it is a
restriction.

Good point. I think there is a bug there. The sentence immediately before the
formal definition says "By 'restriction' is meant the definition of a datatype
whose ·value space· and ·lexical space· are subsets of those of its ·base
type·." which implies that a type cannot be a restriction of anything other
than its base type (that is, it is an intensional rather than extensional
relationship). But the definition that follows suggests a purely extensional
relationship.

I don't think it matters much, because having defined the term ·restriction·,
we only use it four times (within the middle dots), on one occasion incorrectly
(where it is referring to restriction as a process, a method of derivation,
rather than as a relationship between two types). But it's certainly a classic
case where we are using language that looks formal but are actually pretty
fuzzy.


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