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Re: [Xen-API] XSDL schemas for Xen virtual machine configurations


You're most welcome to kick this off which whichever type of schema you
think is appropriate.  I think [without lots of experience to back it
up, mind you] that something simple would be fine for now, leaving the
more complicated contraints to domain logic.

My [less valuable] 2 US cents.

On Wed, 2006-08-02 at 05:04 -0400, Daniel Veillard wrote:
> On Wed, Aug 02, 2006 at 09:21:09AM +0100, Ewan Mellor wrote:
> > On Tue, Aug 01, 2006 at 03:21:06PM -0400, Andrew D. Ball wrote:
> > 
> > > Please pardon my ignorance if this had already been discussed.
> > > 
> > > Has there been any work on standardizing schemas for Xen virtual machine
> > > configurations?  I really like XSDL schemas instead of DTD's.
> > > Regardless, I'd like to have schemas that
> > > 
> > > (1) Indicate which version of Xen they require.
> > > (2) Enumerate exactly which options are available.
> > 
> > As far as I know, there's no-one working on XSDL schemas for this, no.  I 
> > did
> > intend to put together a DTD, though I've not done it yet.  I've no idea
> > whether XSDL schemas or other technologies would be appropriate, though
> > Daniel's reply suggests that there's doubt, at least ;-)
>   Well I was mostly reacting to "I really like XSDL schemas" :-)
> It definitely allows a better checking of the input documents, but
> trying to make one XSD handle evolution and versioning is in practice
> relatively hard.
> > Perhaps you could kick this off, if you are interested?
>   I have an item about this in libvirt TODO. In my experience it may 
> less be useful for validating input at this point (since the format is likely
> to evolve) than as a way to document relatively thorougthly what one may
> find in the XML instance (and hence write the appropriate code handling all
> cases). Sometimes the mapping between the predefined schemas data types 
> and what is the actually acceptable values is where the real usefulness
> of the check, examples:
>   - with DTD you can say a domain has one memory and one name children
>   - with XSD you may refine this stating that the content of memory is
>     a positive integer and the content of name is a string
>   - a better schemas would also check values to make sure memory is at least
>     4Mbytes and less than 16GB and that the name matches [0-9a-zA-Z]* to
>     avoid problems
> Now the amount of effort you take to build a really good schemas is worth it
> only if the instances content is relatively stable, and if many people use it
> as it's harder to define than with a normal programming language. 
>   My 2 euro cents,
> Daniel

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