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RE: What is coupling? [Was: 3 XML Design Principles]

• To: 'Peter Hunsberger' <peter.hunsberger@g...>, Robert Koberg <rob@k...>
• Subject: RE: What is coupling? [Was: 3 XML Design Principles]
• From: "Bullard, Claude L (Len)" <len.bullard@i...>
• Date: Tue, 1 Feb 2005 13:18:22 -0600
• Cc: XML Developers List <xml-dev@l...>

In a myopic answer, XML Doesn't Care.  Data doesn't 
know about coupling and cohesion.

XML is data and data coupling is considered 
the best form, so XML enables better cohesion 
with minimized coupling for modules that process
it.

BUT

XML adds structure in the tree and via metadata such as names.
Metadata and tree structures of the data make 
certain operations on the data harder or easier, for 
example getting and setting node values, so it is 
the case the structure affects the coupling of 
the modules that process the data and their cohesiveness.
Names introduce dependencies for out-of-band knowledge.

Would you rather chase pointers or process a chunk 
in a single pass?  It depends.

Do you care that attribute names can't be repeated 
but element names can?  It depends.

Does attribute orthogonality bother you?  No.  Should it?

Are S-expressions are superior?  One move to permathread #5.

Does the CSS syntax combined with the XML syntax reduce cohesion? 
One move to flameWar #3.

len


From: Peter Hunsberger [mailto:peter.hunsberger@g...]
Sent: Tuesday, February 01, 2005 12:43 PM

> Question:
> 
> Is cohesion maximized when the XML structure is flat and uses attributes
> to logically connect or is it maximized when the structure is nested
> hierarchically?
> 
> -Rob

My opinion: if you've got a single file (or data structure) then
you've got cohesion. Certainly the things you've glued together in
that file or data structure may have no logical connection to each
other, but that's a different issue.

To put it another way: XML can provide cohesion and reduce coupling,
the structure of the XML is an orthogonal concern.

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