Passing XML data between applications

[John Martin]

I am trying to understand how applications can use XML to pass data to
one another.  Here is a scenario:  Say I have middleware that
applications must use to pass data back and forth.  The required data
structure if you're going to use the middleware is:

<NCSB-Message>
<Service-Version-Number>01</Service-Version-Number>
<Service-Release-Number>01</Service-Release-Number>
<Accounting-Code-Information>ABCDEF</Accounting-Code-Information>
<Application-Data></Application-Data>
</NCSB-Message>

As the middleware, we don't care how the application structures the data
in the Application-Data tag.  It will most likely be different for each
application.  We're trying to write a DTD to describe this.  So, for
example, one application using the middleware, may have this description
of the Application-Data:

<Application-Data>
<Customer-Number>123456789012</Customer-Number>
<Last-Name>Smith</Last-Name>
<First-Name>John</First-Name>
<DOB>12/25/1995</DOB>
</Application-Data>

Another application using the middleware might describe their
Application-Data this way:

<Application-Data>
<Last-Name>Smith</Last-Name>
<First-Name>John</First-Name>
<Street-Address>95 Madison Ave</Street-Name>
<City>New York</City><State>New York</State><Zip>00921</Zip>
<DOB>12/25/1995</DOB>
</Application-Data>

I'm trying to understand how you would describe this situation with a
DTD.  Would/can you have two DOCTYPE statements, such as:

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE NCSB SYSTEM "NCSB.dtd">
<!DOCTYPE APPL SYSTEM "APPL.dtd">

Where the NCSB DTD is (basically):

<NCSB-Message>
<Service-Version-Number/>
<Service-Release-Number/>>
<Accounting-Code-Information/>
<Application-Data/>
</NCSB-Message>

and another APPL DTD which is (basically):

<Application-Data>
<Customer-Number/>
<Last-Name/>
<First-Name/>
<DOB/>
</Application-Data>

Or how does this work?  I am a very "concrete/practical" learner and
almost all the examples I see in these XML books are in the
"abstract/theoritica" realm.  And I can't even find an abstract
discussion of this particular kind of situation.  Being new to the
newsgroup and XML, I'd appreciate any pointers if anyone knows of a good
"practical" guide to XML development and/or if there is a better place
to ask these type of questions.

Thanks,
John


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