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Subject: Re: [ubl-dev] Re: [xml-dev] Re: [ubl-dev] UBL 2.0 and Schema Extensibility


At 2006-05-16 22:12 +0100, Fraser Goffin wrote:
>>But what if a black-box use of a UBL construct violates UBL ...
>>perhaps because the UBL construct has a required child, but that ...
>
>Hang on, I thought the proposal for extensibility in UBL 2 is to allow
>either foreign namespace or no namespace content.

... as a direct child of the extension element ... what is inside and 
underneath can be anything at all, including UBL 2 or bastardized UBL 
2 since it isn't governed by the same schemas.

By forcing non-UBL as children of the extension, you are guaranteed 
that no-one can put naked UBL as a child of the extension and have it 
mean anything ... it would only mean anything in the context of a 
non-UBL ancestor being the child of the UBL extension.

>In either case this
>is *not* UBL, this is content that has been agreed by the parties that
>are communicating and declares itself to have meaning only to those
>parties.

Sure.

>It is a 'black box' to everyone else since they won't have
>'that' schema. They may of course be using their own.

Each would have their own, yes.

>So this is
>extensibility for non schema owners, in this case everyone other than
>the UBL TC.

True ... but back to your point about using "lax" instead of my 
suggested "skip" ... if it were true there were no UBL elements 
inside of the extension, and UBL is the only schema being used in 
validation, there is no difference between "lax" and "skip" because 
nothing in there would be recognized.  But, since the content may 
have bastardized UBL inside, using "skip" would prevent false 
negatives when using "lax".

>I don't see how any of this violates UBL since UBL is allowing
>arbritary content to be located (but declared explicitly as *not*
>being actual UBL) at specific locations in its content model.

Sorry, again I wasn't clear ... what I meant was that if an extension 
utilized a UBL construct that itself wasn't valid with the UBL 
schemas but was valid in the extension schemas (I'm not saying it is 
a good practice, but I can imagine someone "borrowing" a UBL 
construct and subsetting it for extension purposes to the point of it 
not being valid to the original UBL).

>Am I missing something here (I'm only on rumours about how
>extensibility will be introduced in UBL 2 since nothing appears to
>have been published officially as yet) ?

Just that inside the extension element is free game ... which might 
for some include invalid UBL constructs ... which I wouldn't like to 
see "caught" by using "lax" for the validation of the extension 
element (and I'd love to write more about extensibility but the UBL 2 
schemas that support extensibility won't be completed until some time 
after next week's plenary UBL session in Brussels ... which also 
gives time to NVDL vendors to come out of the woodwork and improve 
their products ... I'm quite excited to write about and demonstrate 
the extensibility as I'm teaching it in August in the hands-on UBL course.

>Maybe your saying that the content model of the extension may itself
>use constructs defined by UBL.

Yes, indeed I am.

>But in that case wouldn't that violate ##other ?

No, because my understanding is that ##other applies only to the 
child elements of the extension element, and by saying "skip" then 
anything can be used inside those child elements because they are not 
being validated in any way.

>and if you put it in your own namespace then really its not UBL even 
>if it looks remarkably similar and the intended semantics
>are identical ?

Correct because one wouldn't be using the UBL schemas to validate it, 
they would be using their own extension schemas and would not be 
claiming them to be UBL compliant since they aren't trying to be 
standalone UBL instances.

I'm appreciating this discourse, Fraser ... thanks.  And I hope I've 
convinced TC members who are listening about what to use for the 
syntax of the extension element (you there Mike G.?).

. . . . . . . . . . . . Ken

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