- From: Gregor Karlinger <gregor.karlinger@iaik.at>
- Date: Wed, 10 Jul 2002 09:26:32 +0200
- To: <merlin@baltimore.ie>
- Cc: "XMLSigWG" <w3c-ietf-xmldsig@w3.org>
- Message-ID: <023e01c227e3$1e382290$2305a8c0@iaik.at>

Merlin, > Hi Gregor, > > No, you're missing nothing; the spec is missing a stack > of the values of Z. So, in your example, when you pop > out of Select, we should restore the previous value of > Z, which is false. > > Should the text be something like this, or are things > getting too complex? > > * Any time a node N is encountered that is in any evaluated > node set S, push the value of Z onto a stack, update Z > to be the value of filter(N), and then process N and its > descendants. Finally, pop the previous value of Z from > the stack and continue. > > filter(N) is true if and only if the node N > is present in any subtree-expanded union node set and > all subsequent subtree-expanded intersect node sets but > no subsequent subtree-expanded subtract node sets, or > false otherwise. If there are no subsequent intersect > or subtract node sets, then that part of the test is > automatically passed. I think the text is correct now. However I am not convinced if the runtime savings are high enough to justify the additional step of (a) checking each node's existence in the set S of any filter (b) maintaining the stack Wouldn't it be sufficient to have instructions like: Process each node in the document, adding each node to the filter node-set if and only if the node is present in any subtree-expanded union node-set and all subsequent subtree-expanded intersect node-sets but no subsequent subtree-expanded subtract node-sets, or false otherwise. If there are no subsequent intersect or subtract node-sets, then that part of the test is automatically passed. Regards, Gregor > > Merlin > > r/gregor.karlinger@iaik.at/2002.07.08/18:41:22 > >part multipart/signed 16K > >Content-Type: text/plain; > > charset="US-ASCII" > >Content-Transfer-Encoding: 7bit > > > >Merlin, > > > >> r/gregor.karlinger@iaik.at/2002.07.08/12:48:30 > >> >I have the following comment on the current XPath filter > 2.0 draft: > >> > > >> >The first bullet of the inner list in the performance paragraph in > >> >section 3.4 says: > >> > > >> > "Any time a node is encountered that is in any evaluated node > >> > set S, update Z ..." > >> > > >> >I think this is incorrect. The flag Z must be updated for > >> each node of the input node set. > > > ><merlin> > >> I think that the flag Z can only change state if a node from > >> a filter node set is encountered. > ></merlin> > > > >Merlin, maybe I misunderstand what is said in the draft, but let me > >work out the specified algorithm with the following example: > > > > Sample input: <Root><Select/><DontSelect/></Root> > > Transform params: single intersect filter, xpath="//Select" > > > >Step 1: For each XPath expression X, in sequence, evaluate the > > expression and store the resulting node set, S > > > > We only have one filter, whose node set S is {Elem(Select)} > > Filter("Intersect", {Elem(Select)}) > > > >Step 2: Prepend a node set consisting of just the document node, > > along with the operation union. > > > > So we have another filter > > Filter("Union", {Doc} > > > >Step 3: Create a new, empty filter node set. > > > > OK, denote it FilterNodeSet({}) > > > >After the first three init steps we have the following setting: > > > > InputDocument({Doc, Elem{Root}, Elem{Select}, Elem{DontSelect}) > > FilterList ( > > Filter("Union", {Doc} > > Filter("Intersect", {Elem(Select)}) > > ) > > FilterNodeSet({}) > > FlagZ(undefinded) > > > >Step 4: Iterate through the input document in document order, > > adding each node that is encountered to the filter node > > set F if a flag Z is true. This flag is computed as > > follows: Any time a node is encountered that is in any > > evaluated node set S, update Z ... > > > > first iteration: Doc > > > > - Doc is in first filter node set, therefore update flag Z: > > - Last "Union" filter is our first filter > > - Doc is not in subsequent expanded "Intersect" filter node > > set => FlagZ(false) > > > > - Doc will not make it in the FilterNodeset > > => FilterNodeSet({}) > > > > second iteration: Elem(Root) > > > > - Elem(Root) is in no filter node set, so do not update FlagZ > > => FlagZ(false) > > > > - Elem(Root) will not make it in the FilterNodeset > > => FilterNodeSet({}) > > > > third iteration: Elem(Select) > > > > - Elem(Select) is in the second filter node set, therefore > > update flag Z: > > - Last "Union" filter is our first filter > > - Elem(Select) is in the subsequent expandend "Intersect" > > filter node set => FlagZ(true) > > > > - Elem(Select) is our first member of FilterNodeSet > > => FilterNodeSet({Elem(Select)}) > > > > fourth iteration: Elem(DontSelect) > > > > - Elem(DontSelect) is in no filter node set, so do not update > > FlagZ => FlagZ(true) > > > > - Elem(DontSelect) will make it in the FilterNodeset, since > > FlagZ is still true. > > => FilterNodeSet({Elem(Select), Elem(DontSelect)}) > > > >So, if this interpretation of the specified algorithm is correct, we > >have a FilterNodset({Elem(Select), Elem(DontSelect)}, although the > >intention of the filter should be to select Elem(Select) only. > > > >Am I missing something here? > > > >Regards, Gregor > >[32m > >Verification Successful > >[0m > > > -------------------------------------------------------------- > --------------- > The information contained in this message is confidential and > is intended for the addressee(s) only. 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Received on Wednesday, 10 July 2002 03:29:11 UTC