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RE: Schemas as Promises and Expectations

consumer schemas
To me, a schema, is a mechanism for the _partial_ validation of an 
XML document. It is useful as a tool to address some of the more 
tedious parts of that validation process. Also, I look at the problem 
such that there may actually be at least three schemas. One for what 
the producer actually emits, one that is the agreed upon schema for 
interchange, and a third that is used by the consumer to aid in its 
processing of the document. The first producer schema is generally a 
subset of the interchange schema, but the relationship between the 
interchange and the consumer schema may be such that neither is a 
subset of the other and that they are merely intersecting sets. I 
believe that the decoupling of the interchange and consumer schemas 
may prevent a lot of consumer implementation issues from creeping 
into the interchange schema. What I believe you are talking about in 
your three points below are IMO consumer schema issues and should not 
be in the interchange schema.

Don Bate

At 4:29 AM -0800 3/9/03, Don Park wrote:
>Both Perry and Thomas understood what I was trying to say and issues they
>point are tangible.  But I don't think all of what I am thinking has been
>communicated, so allow me to try again from another angle.
>A schema is a formal description of an XML document.  In a sense, the schema
>is a representation of the code that produced that XML document.  But there
>is no similar representation of the code that consumes those XML documents.
>Such representation will be useful for:
>1. documenting which parts of an XML document a program depends on.
>2. detecting when a program can't process a document.
>3. automatically fix useful subset of possible differences.
>For example, there are many versions of RSS format, but a RSS reader that
>uses only the <description> element can handle RSS feeds in any RSS format.
>But there is easy way to determine this without some smart code analyzer.
>Having a schema representation of the parts the RSS reader is interested in
>will be pretty useful.  Unfortunately, I don't think current schema
>languages support this use-case well.
>Don Park
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Don Bate               | Specializing in Consulting and Mentoring in
Bate Consulting, Inc   | Object-Oriented Technologies,
                        | Software Architecture, and Software Process
(972) 618-0208 voice
(972) 618-0216 fax


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