Re: ANN: XML Schema: DOs and DON'Ts

[Eddie Robertsson <eddie@allette.com.au>]

> > On a side issue: Why does this constaint on restriction apply to <xsd:all> and
> > <xsd:choice> groups? It's logical for <xsd:sequence> since the sequence is
> > important but in <xsd:choice> and <xsd:all> the order is insignificant.
>
> I guess there is a computational difficulty issue involved. Otherwise
> it's just an error somehow survived the reviews.
>
> It becomes very hard to check that a given <all> is a proper subset of
> another <all> if you allow arbitrary order of items. If <all> has x items,
> then you have to check x^2 times in the worst case.

You're correct. I found this in the spec [1].

"NOTE: Although the ·validation· semantics of an all group does not depend on the
order of its particles, derived all groups are required to match the order of their
base in order to simplify checking that the derivation is OK."

Cheers,
/Eddie

[1] http://www.w3.org/TR/xmlschema-1/#rcase-Recurse