[xsd-users] warning with any

[Boris Kolpackov]

Hi Ray,

Rizzuto, Raymond <Raymond.Rizzuto at sig.com> writes:


> I can see where the ambiguity would occur in certain cases, such as with
> optional or sets, but for a sequence of A, B, ##ANY, where A and B must
> appear exactly 1 time, an A or B in the ##ANY slot shouldn't be
> ambiguous.

It is not in the XML Schema sense. It is, however, in the case of the
XSD-generated parsing code. Since XML Schema validation is performed in
the underlying XML parser we try to make the parsing code as small as
possible. As a result, it is a simple loop that iterates over elements
and tries to match them in order of appearance. In your original example,
you have an optional element 'ticket' followed by required element 'price'
which is following by the wildcard. In the content like this:

<price>
<ticket>

The 'ticket' element should be matched by the wildcard but the generated
parsing code will match it to the 'ticket' element which is missing in
the content.

In this particular situation the loop-based approach does not appear
to be simpler than the alternative that would parser each element at
a time and then move to the next one. Things, however, get more
complex once you need to handle nested choice/sequence compositors.


> Does the warning occur for ##ANY, regardless of that?  I.e. the warning
> is not taking the context into consideration, just telling the author to
> be advised?

No, the compiler only issues the warning when the mis-match can actually
occur.


> Since I am not the schema author, I can't really make changes, but I'll
> raise the question with the author.  I believe he has the ##ANY in so
> that a future version of the protocol will be compatible with the
> current version.  I.e. a 1.3 version with a new field added at the end
> of the sequence will still talk to the 1.2 version I am coding.

In this case I would assume that the 'ticket' and 'price' elements cannot
appear in place of the wildcard in version 1.3 and thus the warning can be
safely ignored (this is probably the case in 99.9% of the situations this
warning is issued).

Boris