There seems to be a number of problems being addressed in the current discussion:

1) Gregor's original post asked for a solution ("how do I do an include in XML") without posing a problem ("how do I maintain a separate global character list and link a number of independent taxon descriptions to it"). I would suggest that using an "include" is only one of a range of solutions to this problem. And if this isn't the problem then we should revisit it before spending too much time coming up with a solution.

2) Whether XML is hierarchical or relational is of little importance in practice. All major relational databases can suck in and spit out XML - it's a non-issue from an implementation standpoint (which is what we are ultimately concerned with here). IDs and RefIDs are primary and foreign keys - the mapping is one-to-one if you want to structure the XML that way.

3) Leigh is spot-on when he says "define a model for the data" as this is "separate to the details of its [the model's] syntax". The syntax (= XML model) will be useless if it doesn't manage the information that's important to us no matter how "rigorous" or "technically accurate" it is.

4) At the Sydney meeting I thought we agreed to restart this discussion with specific examples based on real-life characters (in the biological sense). This current thread would seem to be very much a continuation of the one started 2 years ago: 80% focus on solutions (largely round XML syntax) and 20% on specific problems (addressing business needs). I fear we'll end up the same place we were before.

Thanks, Steve

Steve Shattuck CSIRO Entomology biolink@ento.csiro.au

P.S. - A solution to Gregor's problem would be to use unique identifiers (GUIDs) in his global character list. Any one using this list would then include these identifiers as part of taxon descriptions along with metadata (a citation) to find where the global list is housed. If you then want to combine separate description datasets you can compare the character identifiers: if they are the same then it's the same character, if they are different then it's not the same character. It's a simple, foolproof solution that's easy to implement technically (whether people will actually do this is a completely different matter ;-) ).

P.P.S. - I'm well aware that I have the power to direct this discussion by actually doing what I suggest in No. 4 above. And I really, really intend to do it. I just have one more meeting to get through, and then another 10 emails, and then ....