15 Nov
2010
15 Nov
'10
3:29 p.m.
---- On Mon, 15 Nov 2010 00:45:04 -0800 Tudor Girba wrote ----
Hi,
Thanks for this nice overview. I am happy that XML handling gets a bit more traction in
Smalltalk :). I took a quick look and your XMLPluggableElementFactory sounds quite
interesting, and it's great that it supports namespaces.
Regarding Opax, your analysis is not quite right.
- You do not need to subclass the OPOpaxHandler.
Really? So if I have a pre-existing SAX parser, say SVGSAXParser, there is a way to make
it support Opax-like functionality without changing its superclass to be that of
OPOpaxHandler?
- The goal of Opax is not to replace DOM, but to
enhance SAX. It's true that at the moment it still creates a tree, but this should be
changed to make it optional. The original idea of Opax was to dispatch everything,
including the factory decision to the Element, but the implementation remained behind the
wishes.
To be perfectly honest with you, I did not before nor do I now fully understand what Opax
is supposed do. I understand that at the very least it involves mapping elements in an XML
document to different kinds of objects, but how it is ultimately supposed to go about
doing this remains unclear and appears to still be in flux.
- Opax is tiny: 3 classes + 4 test classes
True, but it takes up two top-level class categories and still adds more weight to the
package, and by your own admission it stands to only get bigger.
- OPGenericElement should simply be made a subclass of
XMLElement, and we would have the compatibility we would need.
Right, but then it would be a DOM node, and you said you wanted Opax to avoid DOM, or at
least the DOM parser.
- I do not see the reasons why DOM should be preferred
to SAX. The problem with DOM is that it always creates XML elements :). When you have
large XML files, you often do not want to load them, but just to process them directly.
This is the goal of SAX, but then SAX is procedural. Opax should be used to transform SAX
into an object-oriented handling.
So the goal is something that only produces objects for certain portions of a document,
but ignores the rest? I think this could be better built on top of the DOM parser, perhaps
as a partial DOM parser.
Instead of removing it, I would suggest a different
approach. Let's make it focus on the SAX parsing:
- We could easily get it to use the XMLNodeFactory
- We could subclass OPGenericElement from XMLElement.
I think an approach that used more metaprogramming and dependency injection rather than
inheritance would be better. Maybe something that uses reflection to query injected
classes to be used for elements and then fills their instance variables based on the names
of those variables and the names of the child elements and attributes that the elements
the class has been mapped to contain. In other words, you wouldn't need to subclass
OPGenericElement OR XMLElement; just have instance variables in the injected class with
names matching, roughly, the attribute and child element names of the elements the class
has been mapped to. You could also support explicit conversion instructions. For example,
something that could be told to map "timestamp" elements to the DateAndTime
class and to convert their content using fromString:.
In any case, regarding packaging, I would definitely be
in favor of splitting XMLSupport in multiple packages.