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Subject: Customising and versioning
I've been out of touch with UBL lately (admin problems) but I've been having fun trying to work out the W3C Schema derivation techniques again, trying to explore what can be done with the UBL 1.0 schema files compared with UBL 2 schema files. This was prompted by Ken's push for using W3C Schema after all with subsets but I've been concentrating on the version issue primarily (I thought, Get that one solved and the rest should be easy). Well I seem to have got the hang of it enough to produce some derived minor versions of UBL 1.0, UBL 2 prd 1 and UBL 2 prd 2. All three presented different 'problems' (or 'requirements') due to the changes in the NDR, especially related to whether namespaces change with minor versions. The result, as far as I could work things out, was that UBL 1.0 allows derivation with substitution groups (despite that being at odds a bit with UBL NDR 1.0) as does UBL 2 prd 1, whereas UBL 2 prd 2 requires use of redefine (which I did manage to get to work nicely). My conclusion is that UBL 2 may be more difficult to customise by W3C derivation than UBL 1.0 since it may be difficult to use these techniques if UBL minor versions already use redefine for UBL 2. UBL 1.0 allows use of substitution groups for minor versioning (though that may be academic), with limitations due to non-total global design, which would possibly allow further use of substitution groups for customisation of such minor versions. If UBL 2 doesn't use derivation for minor versions, it allows derivation using substitution groups as long as the namespaces are changed in the derived schema files (hence the effect of not allowing such namespace changes for minor official versions limits techniques to redefine or redeclaration, I find). Customising a minor version of UBL 2 would be improved if the namespaces changed if there was still a desire to use derivation for such minor versions. It would then be possible to create substitution group minor versions which could be further customised by substitution groups mechanics. Extensions do not seem to have any negative impact on the above: redefine for minor versions of UBL 2 and substititution groups for customised, changed namespace versions are still possible. It might therefore be feasible for more extreme customisation to add ID/IDREF anchor points where needed in the UBL document schemata using derivation and then use these in an extension :-) I haven't yet managed to do any customisation of datatypes using these methods in earnest. Maybe I'll try that next. All the best Stephen Green
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