16 Nov
2010
16 Nov
'10
11:27 a.m.
Hi,
On 15 Nov 2010, at 15:29, jaayer wrote:
It's the same as with your XMLDOMParser: you do not subclass it, you just parameterize
it. In your case, the parametrization is quite nice.
Yes and no. It would be a DOM node, but this does not mean that we have to store all of
them in a tree if I do not need them.
With the new Factory, the DOMParser is similar to what the OPOpaxHandler is doing. The
difference is that the Factory is doing the mapping, while in Opax the mapping is done on
the class side of the element.
I do not see what would be gained with this because I do not see for what else I could use
these classes. In any case, I would not go the path of playing with instance variables as
long as there are simpler ways.
All in all, I think that the DOM starts to do a good job at creating a tree. I would
propose in moving Opax towards an on-the-fly analysis of the parsed tree but without
storing it (you basically most of the time only need the current stack = the path to the
root).
Cheers,
Doru
--
www.tudorgirba.com
"Sometimes the best solution is not the best solution."
---- On Mon, 15 Nov 2010 00:45:04 -0800 Tudor Girba wrote ----
:). No, and you are not supposed to. The reason for subclassing the SAXHandler is to
accommodate the stream of XML nodes in methods like startElement:... . The OPOpaxHandler
overrides these methods and creates corresponding nodes and dispatches to them the
handling.
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:.