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Subject: RE: [sca-assembly] ISSUE 8: SCDL artifact resolution underspecified



Dale,

A good note that covers many of the considerations - I have a couple of comments.

Yours,  Mike.

Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014    Mobile: +44-7802-467431  
Email:  mike_edwards@uk.ibm.com


"Moberg Dale" <dmoberg@axway.com> wrote on 07/02/2008 20:47:52:

>  

> > Section 12.2.1 "SCA Artifact resolution" [1] indicates there is an SCA
> > defined resolution mechanism (imports and exports).  Are you  
> > objecting to
> > Henning's proposal for a scaLocation attribute (I don't understand
> > Henning's proposal)?  Or are you objecting to the location  
> > attribute on the import element?
> >
> > Honestly, I've never quite gotten the point of Issue 8.
> I'm not sure I do either but it appears that Henning is concerned  
> with the performance of using references to QNames which are defined  
> in artifacts contained in the same contribution. For example,
>  
> <implementation.composite name=”foo:BarComposite”/>
>  
> Where foo:BarComposite is defined in a file contained in the same  
> contribution archive.
>  
>  
> To help me understand this discussion it would be useful to have a
> few clarifications.

>  
> 1. Which attributes of which elements make use of qname values to
> refer? Could URI references or xpointers be used instead?

>  

I think the problems with URI references are exactly the problems
that people encounter with them on the Web - broken links when things
change or move.  A URI is a fine thing if its target is unchanging.

I think we are deliberately trying to accommodate systems that have
change.  This is typical of real enterprise systems.


> 2. For the qname prefixes (the part before the ‘:’), where is the defining
> relation to a URI found?
>  
> 3. Is the URI binding that is in scope for a URI of a contribution or of a
> targetNamespace of a scdl file or something else entirely?
>  
> http://www.w3.org/2001/tag/doc/qnameids.html has a good point or two
> on the topic, such as:

>  
> Where there is a compelling reason to use QNames instead of URIs for
> identification,

> it is imperative that specifications provide a mapping between
> QNames and URIs, if such a mapping is possible

> (which I think means to explain how the prefix and URI are
> associated, at least)

>  
>  
>  
>  
> We've implemented this and resolution  
> performance has not been a major impact. Also, if it does become a  
> problem, some type of index could be generated when the contribution  
> archive is generated that would make resolution virtually negligible.
>  

Clearly, there is a possibility for a runtime to generate a lookup index for
QNames when a contribution is made to the Domain.  One other possibility
would be to generate such an index at development time and place it inside
the contribution.  The latter has the problem of requiring maintenance
if changes are made.

>  





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