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   Re: [xml-dev] Java NVDL implementation

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At 2006-05-07 17:33 +0200, bryan rasmussen wrote:
>On 5/7/06, Jirka Kosek <jirka@kosek.cz> wrote:
>>My understanding of NVDL is that its main purpose is validation and
>>JNVDL thus implements standard Java API for invoking validation. So when
>>your document is valid, there is no return. If there are some errors (be
>>it validation problem on NVDL level, or validation errors against
>>particular schema referenced from NVDL) you get these errors (as
>>exceptions, or you can register your own ErrorHandler to handle them on
>>your own).
>My understanding of NVDL is in agreement with yours.

And mine.  I'm looking only for a non-zero return code on any failure 
of validation of any bit, and a zero return code on successful 
validation of all bits.

>But I think most
>developers would want the validation process to lead to an output of
>the seperated xml,

I disagree ... that is not something that I anticipated would need to 
happen in a development environment ... I'd be using XSLT and my 
match patterns would effectively dispatch the input stream to the 
various handlers.

I do agree it is something needed for a training environment, and I'm 
planning to address that for my NVDL training with some custom code.

>this could be used, for example, as the first step
>in a pipeline so that:
>NVDLValid -> handleValidSeperatedXML
>NVDLInvalid -> handleNonValidSeperatedXML
>otherwise I think, that for most applications likely to be
>encountered, the NVDL validation is useless because after NVDL
>validation they will have to (or want to [not the same thing, but most
>people act as if it were]) do the same thing they would have to do
>without NVDL validation, namely seperate out the namespaces.

But I would have anticipated that separating out the namespaces would 
not be helpful because it would lose context.  Certainly in my XSLT 
stylesheet acting on an instance of multiple namespaces I would 
absolutely need to know context and act on a particular subtree based 
on the parent of the apex.  And, as well, even if there was no 
relationship to the parent, in XSLT the entire tree would be 
available to my calculations and transform as I acted on the presence 
of multiple namespaces.

>And if they seperate out the namespaces correctly than it is not a big
>thing to validate the seperated XML, if they seperate them incorrectly
>(really, there are developers I would not trust to do this) well then
>it would be nice if their validation took place after seperation.

Fine, but then it is just an exercise in XSLT or Python/SAX to create 
individual instances out of context and pass each one through 
validation and act on them.

>At any rate if the developer has to seperate the namespaces themselves
>I am sure they are going to want to validate the document after

Fine, but then I don't think NVDL is the tool they need ... NVDL will 
validate the use of namespaces *in the context* of the document 
without disturbing that context and making the entire document 
available for processing as a whole.

Remember that XSLT acts on XPath addresses without validation ... so 
if a stylesheet knows that a document is valid, it can skip its own 
validation and just act on the information items ... and if a 
document is not considered valid structurally before being sent to 
XSLT then there is no assurance the XSLT will work properly.

>And if they are doing that, why not do just that and skip NVDL?

If they don't need the separate namespaces in context, then I totally 
agree: skip NVDL as it doesn't apply.

>The use case for NVDL without some way to hook into the seperated
>streams will seem very small to the average developer, I think.

I disagree.  I think the developer will more than likely be working 
on the whole rather than on the separate bits, otherwise they would 
have to invent their own ways of maintaining context on the separate 
bits to make the processing of them meaningful.

Whereas they can act on the whole in a single process with the 
NVDL-based assurance that the whole mixture of namespaces is as 
expected according to the NVDL script.

I hope this helps.

. . . . . . . . . . Ken

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