XOM API for Processing XML with Java

[Elliotte Rusty Harold <elharo AT metalab.unc.edu>]

At 2:11 PM -0700 9/29/02, O'Brien-Strain, Eamonn wrote:


> In the Sparta XPath subset it is possible to statically determine, 
> just by parsing the XPath expression, whether it selects an element 
> or a string.  There are different xpathSelect*() methods for 
> returning Elements and Strings.  For example:
>
>    Element foo = doc.xpathSelectElement( "/Top[@g='ggg']/Foo[4]"      );
>    String  bar = doc.xpathSelectString(  "/Top[@g='ggg']/Foo[4]/@bar" );
>
> There are also versions that return iterators over Elements or 
> Strings -- in the case of multiple matches the above methods return 
> the first match.
>
> The methods throw an exception when the wrong type of XPath is passed to them.

I can't say I like that, but I also can't say I've thought of 
anything better.  In fact, my failure to think of an API for this I 
actually like is part of the reason I haven't yet added XPath support 
to XOM. I think XPath's weak typing has real impedance mismatches 
with strongly typed languages such as Java. I'm not sure there is a 
good solution for this.

Sparta partially solves the problem in part by restricting the XPaths 
it can handle. Looking at the BNF, it seems your grammar is actually 
a little more restricted than just the abbreviated XPath syntax. For 
instance, no XPath functions or operators in predicates, and no 
support for the node() node test. I suspect the latter is 
particularly important for being able to statically determine the 
type of an expression.
--

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| Elliotte Rusty Harold | elharo AT metalab.unc.edu | Writer/Programmer |
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|          XML in a  Nutshell, 2nd Edition (O'Reilly, 2002)          |
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