Re: [xml-dev] [Summary] Backward and forward compatible schemas ... Re

[noah_mendelsohn@us.ibm.com]

Roger Costello writes:

> <Book>
>     <Title>My Life and Times</Title>
>     <Author>Paul McCartney</Author>
>     <Date>1998</Date>
>     <ISBN>1-56592-235-2</ISBN>
>     <Publisher>McMillan Publishing</Publisher>
>     <Other>
>         <NumPages>345</NumPages>
>         <Other>
>             <Hardcover>true</Hardcover>
>         </Other>
>     </Other>
> </Book>


Yes, and with the changes in Schema 1.1 it will still be possible to do 
this if you want to, or you will be able to write the sort of schema you 
originally proposed, which would validate:

<Book>
    <Title>My Life and Times</Title>
    <Author>Paul McCartney</Author>
    <Date>1998</Date>
    <ISBN>1-56592-235-2</ISBN>
    <Publisher>McMillan Publishing</Publisher>
    <NumPages>345</NumPages>
    <Hardcover>true</Hardcover>
</Book>

Personally, I feel that the nested <other>'s don't scale very well in the 
case where there will be lots of changes.  Perhaps readers of this thread 
will be interested in an analysis I did for the Schema workgroup about 3 
years ago.  It calls out goals like:

* "The same vocabulary may be versioned or fixed repeatedly.  Accordingly, 
the design should be convenient to use even after 20 or 30 such 
revisions."

* "The versioning mechanisms should not presume particular instance 
constructions such as <extension> elements."

There are several more in that spirit. Keep in mind that this was one of 
many inputs to the work we did on Schema 1.1, and is not in all cases 
descriptive of what we decided to do.  I'd point especially to the 
assumptions and rationale section, which I think holds up reasonably well 
as a set of goals and guidelines for approaching the whole "versioning in 
XML business".  It goes on to propose some mechanisms, some of which 
closely map to what we've decided to do Schema 1.1, but some don't. 
Anyway, it's at [1] in case anyone's interested (it's labeled "rough 
draft", but no cleaner version was ever done).

Noah

[1] 
http://lists.w3.org/Archives/Public/www-tag/2004Aug/att-0010/NRMVersioningProposal.html

[1] 
http://lists.w3.org/Archives/Public/www-tag/2004Aug/att-0010/NRMVersioningProposal.html



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Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
1-617-693-4036
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