[Zope] Zope Book mentions "Fragility"

[Brad Allen]

Hi, I'm a Zope newbie, still in the process of reading the 
documentation and working on my first Zope project. I'm at the stage 
of organizing all my scripts and DTML documents in a folder 
hierarchy, but am unclear on how to design against the "fragility" 
issues discussed in the Zope book. Should I try to avoid a deep 
folder hierarchy and go with something more flat (but less 
well-organized?) Does anyone have any recommendations for me?

Thanks!

(see below for the excerpt from the Zope book)


http://zope.org/Documentation/Books/ZopeBook/2_6Edition/ScriptingZope.stx

Fragility

Over-use of context acquisition can also lead to fragility. In 
object-oriented terms, context acquisition can lead to a site with 
low cohesion and tight coupling. This is generally regarded as a bad 
thing. More specifically, there are many simple actions by which an 
unwitting developer could break scripts that rely on context 
acquisition. These are more likely to occur than with container 
acquisition, because potentially every part of your site affects 
every other part, even in parallel folder branches.

For example, if you write a script that calls another script by a 
long and torturous path, you are assuming that the folder tree is not 
going to change. A maintenance decision to reorganize the folder 
heirarchy could require an audit of scripts in every part of the site 
to determine whether the reorganization will break anything.

Recall our Zoo example. There are several ways in which a zope 
maintainer could break the feed() script:

Inserting another object with the name of the method
This is a normal technique for customizing behavior in Zope, but 
context acquisition makes it more likely to happen by accident. 
Suppose that giraffe vaccination is controlled by a regularly 
scheduled script that calls Zoo/Vet/LargeAnimals/giraffe/feed. 
Suppose a content administrator doesn't know about this script and 
adds a DTML page called vaccinate in the giraffe folder, containing 
information about vaccinating giraffes. This new vaccinate object 
will be acquired before Zoo/Vet/vaccinate. Hopefully you will notice 
the problem before your giraffes get sick.
Calling an inappropriate path
if you visit Zoo/LargeAnimals/hippo/buildings/visitor_reception/feed, 
will the reception area be filled with hippo food? One would hope 
not. This might even be possible for someone who has no permissions 
on the reception object. Such URLs are actually not difficult to 
construct. For example, using relative URLs in standard_html_header 
can lead to some quite long combinations of paths.

Thanks to Toby Dickenson for pointing out these fragility issues on 
the zope-dev mailing li
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.zope.org/pipermail/zope/attachments/20031116/ece84357/attachment.html