[Bug 7242] Type inconsistencies introduced by inheritable attributes

http://www.w3.org/Bugs/Public/show_bug.cgi?id=7242





--- Comment #2 from Peter.Geraghty@tracegroup.com  2009-08-10 10:03:52 ---
I see that I have jumped to some conclusions that the "inheritable attributes"
feature was more significant than it is.

The idea of an "inheritable attribute" in a wider sense is fairly common (e.g.,
as used in the conference / meeting start-date example), and it is probably
confusing that "inheritable attribtues" are described as a new feature in
Schema 1.1 when in fact this is just a constituent of the CTA feature.  At the
present time there are quite a lot of schemas which have accompanying
explanation that semantically some attribute (e.g., currency) is to be treated
as inherited if not explicitly specified on descendant elements. I had
(incorrectly) assumed the "inheritable attributes" feature was to be a means of
formally expressing this within the schema. You could imagine the
schema-for-schemas written differently using such a feature instead of the
current arrangement of a "blockDefault" attribute defined inside
schema-for-schemas plus an explanation elsewhere that this was to be considered
in the absence of a block attribute on a complex type definition.

Inheritable attributes with a rather narrow and esoteric signficance don't
leave a comfortable feeling though and I would like to make a few more points.

1. The motivation for CTA seems to be support for Atom.  Are inheritable
attributes needed for Atom?  I.e., should Atom type determination consider some
attributes of ancestors but not others?

2. Is there an alternative whereby the spec just says that CTA expression
evaluation requires ancestral attributes to be considered?

3. If in fact the Schema 1.1 intention is to be able to use inherited attribute
values in "assert" expressions, but no intention to expect XPath XDM to be
changed we would be in a confusing situation where a schema assert behaved one
way but the exact same expression in Schematron behaved differently.

4. If there is pressure in future to make this feature more general than just
CTA the issues already discussed will have to be considered, and the fact that
there may be schemas out there by then will make it more difficult to rein back
on the latitude allowed.

5. There are implications for inherited attributes with regard to document
fragments and XML canonical form.  Is this a concern that needs to be thought
through?


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Received on Monday, 10 August 2009 10:04:01 UTC