Paul Hammant wrote:
>
> Peter Donald wrote:
>
> >I was thinking about something as simple as current setup.
> >
> >ie
> >
> >vois storeConfiguration( String application,
> > String block,
> > Configuration config );
> >
> Hmm, that forced the comp writer to have some way of constructing an
> tree of Configuration objects themselves. I'd guess getting it right is
> a high art and buckets of code. Though there are good points raised
> about reliance on Xpath and it's implicit underlying XML document, I
> think it's a simple think for component writers to use.
There are issues beyond that as well. XPath is in no way simple. It's
actually a potentially very complex and highly flexible language that
maps well to XML documents, but not necessary well to non-XML
structures. It's definitely not easy to write an XPath implementation
(as the Xalan people). Beyond that, there are other issues, like the
nature of selectors, for example:
//node()
Is a perfectly valid XPath selector that recursively selects *every*
node in a tree. This includes elements, attributes, text, cdata,
comments, etc.... If you were to use this XPath as a selector for
performing a modification to a tree, you'd end up touching the entire
tree, which could be very bad. There are also the functions that return
non-nodesets, and may modify the values of the returned values in the
process.
I would propose a terse, simplified pathing system that does not support
functions, all-descendent/ancestor axis, and many of the other nice
features of XPath that neither translate well to a configuration model,
or translate well to a non-XML structure.
Another possibility, is to just stick with method calls (ex):
cfg.getChild("somechild").getChild("anotherchild").getValueAsLong();
For two reasons:
1 - Though verbose, it provides the same functionality a terse pathing
form would.
2 - It's structural validity can be qualified at compile-time.. XPath
would require run-time validation.
--
Tom Bradford The dbXML Group, L.L.C. http://www.dbxmlgroup.com/
Desktop, Laptop, Settop, Palmtop. Can your XML database do that?
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