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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XPath and XPattern (was Re: More on tamingSAX)
 >> Say the test was /foo/bar/[baz2="test"]/baz1 >> >> <foo> >> <bar> >> <baz1/> >> <baz2>test</baz2> >> <baz3/> >> </bar> >> </foo> >> >> If your schema stated that the children were (baz1,baz2,baz3) >> wouldn't you have enough information to know to surrender when >> you reached baz3? Essentially in order to make a useful case of this (surrendering at baz3) you would need to cache all previous events so that they could be replayed when the predicate's boolean value was determined. Unfortunately that solution doesn't win much against the DOM or other tree based models. The *trick* is to know when you reach baz1 so that you can begin doing interesting things with the chain of events as they happen. Now, the Schema Assisted Sipping that you mention might broaden the cases that predicates would be useful but they are still limited. For example if your schema asserted (as you say) that the content model of bar be (baz1, baz2, baz3) and that baz2="test" always-- then you could "surrender" at the point of baz1 by starting with the assumption of validity. If the document turns out to not be valid you could raise some special error that says essentially-- hey we assumed this was valid and it isn't so we don't know if we reported the right thing or not. There is still a group of solvable predicates too, like: /foo/bar[baz2="test"]/baz3 Here the predicate's boolean value will be known before the startElement for baz3 is reached. The question is: is it worth defining a constraint for this in plain language or in grammar, or should predicates be nixed entirely? If we aim for defining the constraint then I would suspect that we will find a wealth of information on this exact subject on the STX list (as Christian mentioned)-- but ultimately it appears that they decided no such constraint would appear in their language. In XML Schema's stripped down XPath, predicates are not permitted. All the best, Jeff Rafter 
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