Compound Documents - necessary for success?

[Roger L. Costello]

Marcus Carr wrote:

>Sorry, maybe I didn't make myself clear - given the following DTD:
>
><!DOCTYPE doc [
><!ELEMENT doc      (a?, b?, c?)>
><!ELEMENT a        (#PCDATA)>
><!ELEMENT b        (#PCDATA)>
><!ELEMENT c        (#PCDATA)>
>]>
>
>If a user wants to create a compound document, they might do something
like:
>
><doc>
>  <c xmlns="http://MyDTD">This is c</c>
>  <b xmlns="http://MyDTD">This is b</b>
>  <a xmlns="http://MyDTD">This is a</a>
></doc>
>

This presupposes that (a) we know apriori what documents we want to nest
within <doc>, and (b) what order the nested documents are to be in, etc. 
It assumes everything is static.  I was thinking along the lines of a much
more dynamic system in which a document is generated from assembling
together data from a number of different data sources dynamically.  For
example, suppose that you have a number of different meteorological sensors
that generate periodic, transient data.  Each sensor transmits its data in
accordance to its sensor.dtd.  Each sensor has a different DTD.  We would
like to collect together data from some (or all) of the sensors and create
a single (composite) document from this dynamic, transient data.

So, here are the features that I see a composite XML document may have:

(1) The sources of the data may be transient.  The composite document
itself may be transient.
(2) The data is assembled "on the fly".  Which data is selected, the order
of the selected documents is entirely dynamic.
(3) Each data source may conform to a different DTD (grammar).

Consequences:

(1) There can be no DTD for the composite document, unless it is
dynamically created.

>
>> Is it not enough to verify that the fragments are valid and that the
>> document as a whole is well-formed?
>
>No, you also want to respect the original intention of the DTD, unless a
really
>good reason exists not to.
 
What does it buy you to validate the document as a whole when each piece
(fragment) has been validated? 

/Roger


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