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Subject: Customization limitations
Dear UBL TC, This is a comment to point out a weakness in reliance on customization to implement UBL which might need to be noted in future documents about customization and implementation of UBL (perhaps if any revisions are made as a result of the PAS submission). This comment also incidentally supports the decision to exclude a formal calculation model from the UBL semantics so far. There seems to be a serious limitation in the subset concept typically applied to customizations, not only of UBL documents but perhaps more generally too, in that in order to define the semantics of a subset, there may be unintended variation introduced between the semantics of the subset and the semantics of the superset. When this semantics variation involves the calculation model (such as when a subset is made of a customization which includes a calculation model), I think it is likely to have adverse side-effects. For example, in a document there may be an entity to apply a rounding value to amount totals; if the subset does not include this entity but the subset includes a calculation model, it is possible that the calculation model will exclude the rounding value. This factor may be irrelevant if the subset does not allow inclusion of non-subset entities outside its own syntax in documents. However, if the subset does allow a document to include the rounding value then its semantics and in particular its calculation model will need to handle this as an issue. In such a case, I think UBL needs to warn implementers, the designers of the semantic subset need to be aware and make it clear how such a document is to be handled. The same applies, I think, to the case of multiple subsets where interoperability is sought between them. I suggest this be noted in future UBL documents and perhaps some other means be used to warn UBL implementers. Best regards ---- Stephen D Green
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