To clarify a little.

 

I would see this MCE-esque scenario as something like this:

If the (XML, eg UBL) invoice contains any eneties marked with

a 'MustUnderstand' attribute, say, but my finance app doesn't

have them on, say, a list of entities it already includes properly

in its calculations, then it will reject the invoice (or at least

mark it as an exception which the application cannot process

with regard to its calculations). Likewise, the application

sending the invoice will need to be programmed such that all

calculation-sensitive data can be (and is) marked 'MustUnderstand'.

Obviously there will be more to it than that in real life but it's an

arhictectural pattern for XML (for business documents at least)

I've been after for a long time. It nicely complements and perhaps

completes the architectural pattern of schema subsets.

----

Stephen D Green

On 11 April 2013 08:23, Stephen D Green <stephengreenubl@g...> wrote:

Well with some business-transaction documents such as invoices

there is a calculation model which is very important to get right

when processing the document. The processing application (code)

has to know which entities are important components of the

calculation and which are not. If there are no variations to the

schema (or more specifically to the structure and semantics) the

calculation model is clear. Having a situation where there are no

variations which could impact the calculation model is extremely

optimistic when there are many parties involved, especially when

there are multiple countries and accounting and tax systems

involved. So having a way to always be certain whether a strange

entity is relevant to the calculation model is important to allow

reliable calculations even in a non-homogenous scenario where

there are multiple variations, some known, some unknown (such

as new versions and unfamiliar customisations or even variations

in the use of the same schema)... And that's a simplification.

----

Stephen D Green

On 10 April 2013 16:43, John Cowan <johnwcowan@g...> wrote:

On Wed, Apr 10, 2013 at 7:18 AM, Stephen D Green <stephengreenubl@g...> wrote:

The MCE, mentioned in the other thread, does look quite promising for

future developments of XML standards for Invoices though: If it becomes

possible to label some entities as 'must understand' and others as

'ignorable'.

I used to be a big believer in this distinction.  Then I realized that "must understand" begs the question "in order to do what?"  If you are an editor for office documents, or even a viewer, it may make some sort of sense.  But suppose you just want to count the number of paragraphs with a little bit of XSLT?  Are you supposed to make use of the MCE information in this case?  Obviously not.  But there simply is no bright line between when you should and when you should not, making the whole notion of "must understand" extremely problematic to apply.

There's a nice analogy with what the Open Source Initiative mailing lists call "badgeware".  These are web applications that you can use and modify freely, provided you keep the original creator's logo, or a link, on the splash screen, or even all screens.  The authors always want us to bless their licenses as open source, but they can't be.  Why not?  Because they don't realize how wide the scope of "modification" is.  Suppose you just want to pull out the date-parsing code and reuse it server-side, where there is nowhere to display the badge.  Is that valid according to the license?  Probably not.  And if it is, where can the line be drawn between reusing the whole thing and just changing the logo, and this sort of reuse of individual modules?  Nobody knows.  So we have to turn down such licenses.

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