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Re: Logical relationships between documents and schemata: was Re :using namespaces to version

{ apologies for having to quote so much ... }

On 04/05/2001 18:07:25 Jonathan Borden wrote:

>Let's now examine your first case of how "backwards compatible" might be
>> "instance documents which are valid under (some?) previous versions of the
>> schema remain valid instances under the new schema".
>When Extension(Snew,Sold) all valid instances under the old schema are also
>valid instances under the new schema.
>Now let's examine the second case:
>>"instance documents which are valid under the new schema are also valid
>> the version of the schema against which the application was written".
>When  Extension(Snew,Sapp) all valid instances under the new scheme are also
>valid instances under the "app" schema.
>When Sold = Sapp the two definitions are identical, and so I think that
>these two definitions of "backwards compatible" are themselves compatible.

Unfortunately, the application requirement I was alluding to is
Restriction(Snew,Sapp), which is equivalent to Extension(Sapp,Snew)
(from what I understand of your algebra at "
http://www.rddl.org/SchemaAlgebra.html").  So, the problem remains, but
hopefully more clearly expressed now.

>To the question of how RDDL might help: The designer of a namespace
>(designer of the RDDL document describing the namespace) is free to use
>version specific purposes assigned to each rddl:resource referencing a
>schema. The purpose http://www.rddl.org/purposes#schema-validation is simply
>a well known purpose for describing that a particular schema is used for
>schema validation in a particular namespace. An application might, for
>example, choose to label schemata with version specific purposes.

Yes, but given that my instance document may have elements in an unversioned
namespace URI, for which there are multiple schemas (all listed in the RDDL
document), how do I determine which schema is the correct one?  Remember, the
answer may not be just the "schemaLocation", because if I have schemas importing
or including schemas which themselves import or include schemas, it may be a big
job to determine just what all of the relevant schema versions are.

Anthony B. Coates
Leader of XML Architecture & Design
Chief Technology Office
Reuters Plc, London.

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