From: Jerome Simeon <simeon@us.ibm.com>

Date: Thu, 17 Mar 2005 11:53:27 -0500

To: Philippe Michiels <philippe.michiels@ua.ac.be>

Cc: www-ql@w3.org

Message-ID: <OFCF08843A.8C74ED6F-ON85256FC7.005AEB1B-85256FC7.005CC804@us.ibm.com>

Date: Thu, 17 Mar 2005 11:53:27 -0500

To: Philippe Michiels <philippe.michiels@ua.ac.be>

Cc: www-ql@w3.org

Message-ID: <OFCF08843A.8C74ED6F-ON85256FC7.005AEB1B-85256FC7.005CC804@us.ibm.com>

Philippe, The normalization rule you mention applies only to ForwardSteps, which always return a sequence of nodes. There is another normalization rule which applies to PrimaryExpr (See Section 4.3.2 Filter Expressions): [PrimaryExpr PredicateList "[" Expr "]"]Expr == let $fs:sequence := [PrimaryExpr PredicateList]Expr return let $fs:last := fn:count($fs:sequence) return for $fs:dot at $fs:position in $fs:sequence return if [Expr]Predicates then $fs:dot else () Primary expressions can return any kind of items, and that rule does not force to sort by document order and remove duplicates. - Jerome www-ql-request@w3.org wrote on 03/17/2005 04:48:57 AM: > > Hi, > > I am confused by the normalization of path expressions that have end with a > predicate step (e.g. doc("x")/a/b[c] > > The normalization of filter expressions in the FS, enforces the result of the > step to be a node sequence (because of the fs:distinct-doc-order call). > For instance, for a numerical predicate it goes as follows: > > [ForwardStep PredicateList "[" Numeric "]"]Expr > == > let $fs:sequence := > fs:apply-ordering-mode(fs:distinct-doc-order( [ForwardStep > PredicateList]Expr )) return > fn:subsequence($fs:sequence,Numeric,1) > > But from the XPath 2.0 draft I understand that the result can be a > sequence of > nodes or a sequence of atomic values: > > from (http://www.w3.org/TR/xpath20/#id-path-expressions) > > Each operation E1/E2 is evaluated as follows: Expression E1 is evaluated, and > if the result is not a (possibly empty) sequence of nodes, a type error is > raised. Each node resulting from the evaluation of E1 then serves in turn to > provide an inner focus for an evaluation of E2, as described in 2.1.2 Dynamic > Context. The sequences resulting from all the evaluations of E2 are combined > as follows: > > (1) If every evaluation of E2 returns a (possibly empty) sequence of nodes, > these sequences are combined, and duplicate nodes are eliminated based on > node identity. The resulting node sequence is returned in document order. > > (2) If every evaluation of E2 returns a (possibly empty) sequence of atomic > values, these sequences are concatenated, in order, and returned. > > (3) Otherwise (that is, if the multiple evaluations of E2 return at least one > node and at least one atomic value), a type error is raised.[err:XP0018]. > > I'm wondering wheather the distinct-doc-order call in the FS should > in fact be > a distinct-doc-order-or-atomic-sequence call. > > Thanks, > Ph > -- > Philippe Michiels > Universiteit Antwerpen > ADReM (Advanced Database Research and Modelling) > http://www.adrem.ua.ac.be/~michiels >Received on Thursday, 17 March 2005 16:54:00 UTC

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