[XML-SIG] DOM Considered Harmful :-)
Wed, 05 May 1999 10:54:42 -0400
Greg Stein wrote:
> 2) the close() method and parent/sibling relationships
should work very well for this.
> Adding parent/sibling relationships introduces loops unless you use
> proxies or introduce a close() method (if there is another way, then I'd
> like to learn it). Proxies are out for efficiency reasons -- objects get
> constructed every time you simply want to peek into the data structure.
> While the complexity is (mostly) hidden from the client, it is still
> there. You don't end up with simple data structures... instead, you get
> a lot of "mechanism" in there to deal with intercepting accesses so that
> you can create a proxy to bundle up the necessary data.
I guess that acquisition corresponds to a "proxy" approach.
We have optimized it heavily so performance is not an issue.
Also, acquisition provides a very simple model that adds very
> A close() type method introduces other problems. If you aren't careful,
> then it is easy to leak the entire parse tree. What happens if you pass
> a subset of the tree to another subsystem? You will have one of two
> problems: 1) the client avoids calling close() so the subsystem can use
> parent references (this leaks the whole tree); or 2) the client calls
> close() so the subsystem only retains its subtree, but now its
> (expected) parent/sibling relationsips no longer work. It has a set of
> objects that don't fully respond to their published API.
Acquisition avoids this issue because it eliminates the need
for child refereces to parents.
> I'm tremendously in favor of the model returned by qp_xml.
(BTW, could you provide a link to this proposal?
I must have deleted the message that contained it. I'd
like to look at it.)
Acquisition has worked very well in Zope. It provides a
very nice way to share information in a containment hierarchy.
It's only drawback is that it requires use of ExtensionClass,
which is actually a bonus. ;)
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