[WS-Topics 1.3] TopicExpressions

[Bram Van Dam <bram.vandam@foresee.be>]

Hi,

I've got a bit of a problem with the way that wsnt:TopicExpression deals
with topics and topic namespaces. Supporting multiple dialects is
obviously a good thing, and defining several standard dialects is even
better. Unfortunately, the content of the wsnt:TopicExpression field is
a plain old string. Sure, the content depends on the dialect, but with
all the standard dialects the content is an xsd:token with a very ugly
regex applied to it. This makes it very difficult to work with,
particularly when different namespaces are applied. XML namespace
prefixes are not set in stone, and can change as XML is read and
rewritten. The content of string fields, however, does not change,
regardless of whether or not they are in a QName format.

For instance, if you take the following XML excerpt, run
marshall/unmarshall it with JaxB, it will break:

<Topic
Dialect="http://docs.oasis-open.org/wsn/t-1/TopicExpression/Concrete";
xmlns:tns="myTns">tns:MyTopic</Topic>

Because tns:MyTopic is a string, XML parsers treat it as such. The tns
namespace therefore appears to be unused and might be discarded. Or
renamed, to ns1 for instance, thus rendering the tns:MyTopic string
unusable.

This essentially makes working with the predefined Topic dialects a lot
harder than it should ideally be.

Should any updates to the Topics spec be planned, I think it might be
useful if this were taken into account and that perhaps some other
format is defined.

If I've misinterpreted this part of the spec, feel free to rub my nose
in it  :-)

Thanks,

   - Bram