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I think we've all implicitly agreed that Source is pretty useless. The
primary argument in its favor has been a lot of hand waving and pointing
at some .NET thing, and saying, "That's even worse" but nobody's really
stepped up to defend Source on its own merits.
Here's a perhaps more useful question. Could we define an alternate
source interface that would allow validators, transformers, and query
tools to hook into arbitrary models? Specifically, could we define one
that would be complete, unlike Source; and would not require these tools
to provide special support for each different object model? What would
such an interface look like?
It is, I admit, a hard problem. I suspect it could be solved for
tree-based models by defining some sort of interface based on the XPath
data model. I am not at all sure it's possible to define this for
streaming models as well, but perhaps it is.
Possibly the issues of transforms are different from query tools and
validators. All transform engines I've seen build their own internal
model. They do not work directly on top of DOM, SAX, XOM, or other
things. Validators and query tools, by contrast, tend not to construct
new object models and do work directly on top of the preexisting
in-memory representations of the XML document.
If that's an accurate characterization (I'm not sure it is) then the
needs of transforms would be served by a single interface that just
streamed entire documents into the engine, because the engine is going
to build a new model anyway. On the other hand, query tools might want a
wrapper around an existing tree model that they could query. Validators
could probably work with either.
I'm not sure it's possible to satisfy all use cases with one or other,
but maybe it's possible. If not, perhaps we could get away with two
interfaces instead? e.g. replace SAXSource and DOMSource with
StreamSource and TreeSource. These would be read-only interfaces that
would provide full access to what's needed for the XPath data model.
Each model could implement one interface or the other. Tools could
support one or the other, but I think most would support both. However,
they would only need to support both. The would not need to specially
support JDOMTreeSource, XOMTreeSource, DOMTreeSource, SAXStreamSource,
StAXStreamSource, XNIStreamSource, etc.
Does this seem plausible? Does this seem worth doing? Does anyone have
any other ideas?
--
Elliotte Rusty Harold elharo@metalab.unc.edu
XML in a Nutshell 3rd Edition Just Published!
http://www.cafeconleche.org/books/xian3/
http://www.amazon.com/exec/obidos/ISBN=0596007647/cafeaulaitA/ref=nosim
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