RE: [xml-dev] RE: Concerned about the increasing reliance on XPath

["G. Ken Holman" <gkholman@CraneSoftwrights.com>]

At 2011-05-09 17:50 -0400, Liam R E Quin wrote:
>In most cases there's not much point carrying around precomputed values
>- see Third Normal Form for relational databases for why duplicated
>information is usually a warning flag.  But computing it on the fly,
>processing the augmented document, and then checking the constraints
>still hold, that's another matter.

It is an explicit rule in UBL that *all* computed values are 
expressed in the XML with their final calculated value.  A recipient 
cannot be expected to do any calculation and can only be expected to 
use the evident values found in the UBL document.

Another benefit is that this makes stylesheet writing very generic as 
the stylesheet knows exactly where the information is in the source 
XML and where it belongs in the result rendering but doesn't have to 
know how the values are calculated.

>I would almost certainly expect to have the logic _outside_ the document
>in most cases

Exactly ... we've called that "the calculation model".  A community 
of users needs to agree on that community's calculation model for 
element values found in a UBL document.  Knowing the calculation 
model is good for a recipients validation of the values.

Different communities will have different calculation models for any 
given value in UBL.  It is not up to the standards committee to tell 
users how they have to calculate any particular value.  Just think 
how complex tax rules are in different communities, for example.

But if you don't know the calculation model, you have the numbers to work with.

. . . . . . . . . . Ken

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