[Bug 26453] [xp3.1] Lowest common supertype

https://www.w3.org/Bugs/Public/show_bug.cgi?id=26453

--- Comment #4 from Michael Kay <mike@saxonica.com> ---
The only place in XPath where the concept of lowest/least common supertype is
used is in value comparisons:

"Next, if possible, the two operands are converted to their least common type
by a combination of type promotion and subtype substitution. For example, if
the operands are of type hatsize (derived from xs:integer) and shoesize
(derived from xs:float), their least common type is xs:float."

This rule is unnecessarily complicated. We could simplify it to:

"Next, if the types of the two operands are derived from different primitive
types P and Q, and if P can be promoted to Q, then the operand of type P is
cast to type Q."

Conversion to the LCST within the type hierarchy simply isn't necessary,
because it has no effect on any subsequent operation.

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Received on Wednesday, 17 September 2014 08:28:16 UTC