- From: Aleksey Sanin <aleksey@aleksey.com>
- Date: Mon, 08 Apr 2002 11:28:28 -0700
- To: John Boyer <JBoyer@PureEdge.com>
- CC: merlin <merlin@baltimore.ie>, reagle@w3.org, w3c-ietf-xmldsig@w3.org
- Message-ID: <3CB1E14C.8010308@aleksey.com>
Yes, I have an example. Suppose we have following document: <a> <b> <c/> <d/> </b> </a> If the XPath expression selects node "b" (nodes set S = { node "b" } then the current proposal requires application to create new nodes set S' which will include nodes "b", "c" and "d". This is an additional step. I don't see any reasons why the author of XPath expression will not include these nodes him or herself. Also this additional step limits the XPath filter functionality because one can have a requirement to operate with nodes set having *only* node "b" but not nodes "c" and "d" Aleksey. John Boyer wrote: >Hi Aleksey, > >All XPath implementations operate over actual nodes and not subtree >roots. At any point in time, the resultant node-set of an Xpath >expression is interpreted by the application that consumes Xpath (the >host language, so to speak). For example, XSLT typically uses recursion >to process the nodes in a node-set, so the nodes are interpreted as >subtree roots. > >In essence, a node-set containing nodes that we choose to interpret as >subtree roots is still a node-set containing nodes. > >Therefore, I do not see the basis in fact for your claim that we will >sometimes lose efficiency. Is this just what you suspect will happen or >do you have an actual implementation that is harmed by this approach? > >Thanks, >John Boyer > >-----Original Message----- >From: Aleksey Sanin [mailto:aleksey@aleksey.com] >Sent: Monday, April 08, 2002 10:46 AM >To: merlin >Cc: reagle@w3.org; w3c-ietf-xmldsig@w3.org >Subject: Re: New Version of XPath Filter > > > >>2. We choose to perform expansion from nodes to node trees outside >>the XPath processor to maximize the possible execution speed. It >>is much faster to evaluate and expand //Foo than to evaluate >>//Foo//self::node(). Remember, the only goal of this transform is >>speed; it doesn't provide any new capability. >> >I don't think that there is no new functionality at all. For example, >uninon provides new ways >to apply some transforms to a part of the document and add more nodes >later. Also some XPath >implementations operates on the actual nodes sets (no sub-trees!) and by > >this construction >S' is an additional and expensive operation! > >Aleksey. >
Received on Monday, 8 April 2002 14:29:29 UTC