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

• To: '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 13:13:43 -0600
• Cc: XML Developers List <xml-dev@l...>

No, I'd say you are getting it.  XML Doesn't Care. 
It is just structured/named data.  There are some 
wrinkles to how that works determined by the context of 
use (system rules).

Modules (even XSLT) that use XML do care.  The 
appropriate structure depends on the module. That 
is why we brought up USE nodes.  It's not just 
a pointer; it is what is done with the thing pointed 
to; in the case of a use node, it is copied on 
render but is one data structure in memory.  For 
that application, pointing is faster than having 
a duplicate.  In X3D, deep nesting slows down 
the application.  Put a lot of named primitives 
(spheres, boxes, etc.) into a scene and nest them, 
and the frame rate will drop to sub 4fps rates; 
say, crawls.  Good authoring systems enable this 
to be optimized and flattened into more efficient 
representations like indexed face sets.  The cost: 
it's a one way conversion because information is lost. 
The gain: fidelity to real time.

A more interesting coupling/cohesion study might 
be the effect of certain kinds of standards for 
schema development.  For example, the UBL 
naming standard is itself, 112 pages long. 
That ripples across a lot of other standards. 
Is coupling to that enhancing the cohesion of 
the standards that couple to it?

len

From: Robert Koberg [mailto:rob@k...]

Bullard, Claude L (Len) wrote:
> Cohesion and coupling:
...
> and of course, the ultimate expression of homophilic principles, the Law
of
> Demeter: 
> "Only talk to your friends."  For programmers, there are lots of articles
on
> this one.
> 
> http://www.cmcrossroads.com/bradapp/docs/demeter-intro.html

I am having trouble applying OO to XML, but I read this from the above 
article:

"The Law of Demeter says that if I need to request a service of an 
objects sub-part, I should instead make the request of the object itself 
and let it propagate this request to all relevant sub-parts, thus the 
object is responsible for knowing its internal make-up instead of the 
method that uses it."

To me, if I have a nested structure in an XML instance and using XSL on 
that I apply-templates (flow through the instance doc) and only do what 
is in the XML. If I come across something that is a reference to 
something else I can go out, get it, apply-templates on it and continue 
where I left off.

If I have a flat structure in an instance doc I have to assume where 
things go and place them in a more rigid way.

Am I just not getting it?

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