Just for the record, I now count three gaps with XSD

[stephen.green@systml.co.uk]

I was unable to get to emails in the latter stages of the
recent discussions, sorry.

Just for the record, not wanting to spark further debate
but open to contrary or confirming comment, I now count
that there have been three key areas where UBL work has
found a gap between e-commerce requirements and XSD (W3C
XML Schema) features:

first was ** Subsets ** (hence no schemas provided for the SBS)

second was ** Codelists ** (enumerated datatype restriction and extension)

now the third seems to be ** Extension Points **

We also, historically, had problems with use of substitution
groups for customisation when there were already imports in
the schemas (instances needed different prefix requirements
after customisation from those they had before it).

I also find problems using 'redefine' across 'imports' which
would hinder its use for minor versioning of modular schemas
which already use 'import'. There have been problems trying
to redefine schemas where the redefinitions are needed both
sides of imports (or several imports in UBL's case).

On the plus side though, I did manage to get substitution groups
working to some extent with UBL's CCTS-datatypes in a way which
was CCTS compliant, I think (subsituting elements based on types
based on CCTS 'qualified datatypes' based on CCTS 'unqualified
datatypes'). This was to customise UBL 1.0. Of course there are
known limitations in customising UBL 1.0 this way already being
possibly fixed with the design for UBL 2 (UBL NDR 2).

I'll be presenting my own slant on this later in June at an XML UK
meeting in Reading (Town Hall), UK on coming 27th June at 10.35
BST if anyone is near enough to come and heckle :-)

All the best

Stephen Green