RE: how to sort a list of xpaths

You don't actually say what sort order you want, but the implication is that
you want an order such that if one rule subsumes another (in the sense that
A subsumes B if the set of things matched by B is a subset of those matched
by A) then B should precede A in the sort order.

In the example you have given, it doesn't require a schema to determine that
//class subsumes /section/class or that /section/class subsumes
/section/class[@type='bb']. Of course, given a schema you can do more
sophisticated analysis, but I should start with the basics first.

Although you've expressed your problem in terms of xpaths, your examples are
all XSLT patterns, and you describe the semantics in terms of matching; so
another useful simplification would be to restrict yourself to patterns.

I think the problem then becomes tractable provided you don't try to be too
clever, for example trying to detect that A[contains(., 'abc')] subsumes
A[starts-with(., 'abc')]. However, it's not going to be easy. Your first
step is to get an XML representation of the expression tree (for example,
use XQueryX, or use the output of Saxon "explain"); then find a sort routine
that uses a callback to compare two items in the sequence; and implement
this callback to compare the two expressions. This would use a number of
rules for example that EXP subsumes EXP[P] and that //EXP subsumes PATH/EXP.
There might be quite a few of these rules.

I've actually been thinking of doing this kind of analysis for XSLT template
matching for a while, but there's nothing in Saxon that currently does it,
beyond the basic logic to calculate the default priority of the match
pattern.

Michael Kay
http://www.saxonica.com/  

> -----Original Message-----
> From: Mark Hutchinson [mailto:mark@xxxxxxxxxxx] 
> Sent: 20 January 2008 07:11
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject:  how to sort a list of xpaths
> 
> 
> I have an application that uses xpaths to identify which rule 
> that should be executed for a given tag in a source file.
> 
> eg given a source file of:
> <section>
>     <class type="AA">
>        <entry>entry text</para>
>     </class>
>     <class type="BB">
>        <entry type="italic">text text</para>
>        <entry>text text</entry>
>        <class>
>           <entry>subclass entry text</entry>
>        </class>
>     </class>
> </section>
> 
> My application might have the following rules :
> 
>    1. /section/class[@type="AA"]/entry
>    2. //class
>    3. /section/class[@type="BB"]/entry
>    4. //entry
>    5. //entry[@type="italic"]
> 
> My application searches the rules from the top down - 
> stopping from checking any further once a match has been 
> found. ie the first class
> (AA) matches with rule 1 and this is correct. The second 
> class (BB) matches with rule 2 which is, obviously, not correct.
> 
> Here's my question (finally!) - do anyone have a utility or 
> xslt, perl etc that can sort these rules based on a schema?
> 
> Regards
> Mark H.