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Re: [xml-dev] MicroXPath proposal

Had meant this to go to the list.
> On Sat, Jan 15, 2011 at 10:04 PM, Uche Ogbuji <uche@ogbuji.net> wrote:
> > I agree with the above until the last point.  I also believe that the
> > "streamable" subset of XPath 1.0 is useful, though of course people
> > establish such a subset in several ways.  I'd say XSLT 1.0's pattern
> > language comes close enough for most uses.
On Sat, Jan 15, 2011 at 11:52 PM, John Cowan <johnwcowan@gmail.com> wrote:


> Now that's a *very* interesting idea: the path would allow / and //,
> and the legal path steps are: name, *, @name, @*, text(), and
> id(name).   That's very close to my original proposal.  But patterns
> are no simpler than XPath 1.0 for the implementor, because *any*
> expression can be a predicate in a pattern, so you end up having to
> implement the whole of 1.0 anyway.  What is the simplest set of
> predicates that could possibly work?

Well I might as well offer my own take on that matter.

The predicates bit from


   - numerical predicates

      e.g. a[1]
      - a numerical or positional predicate is only allowed in a step using
      the child axis

         e.g. these are *forbidden*: a/descendant::b[2] and

         but this is OK: a//b[2] since it expands to
         a/descendant-or-self::node()/child::b[2] and hence the predicate is
         on a step using the child axis
         - predicates that only use the attribute or self axis for value

      e.g. a[@attr = 'value']
      - Boolean expressions in predicates

      e.g. a[@id='1' or @id='2'], a[@id='1' and @spam='eggs'],
      a[@id='1' and not(@spam='eggs')]

There might be some quirks/holes in the above, and I might as well have
those pointed out here as anywhere else.

Uche Ogbuji                       http://uche.ogbuji.net
Weblog: http://copia.ogbuji.net
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Founding Partner, Zepheira        http://zepheira.com
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