2708 2006-01-11 21:55:03 +0000 Errors and Optimization and Cardinality checks 2006-02-15 21:59:36 +0000 1 1 1 Unclassified XPath / XQuery / XSLT XPath 2.0 Candidate Recommendation PC Windows XP CLOSED FIXED P2 normal --- 1 mike chamberl public-qt-comments oldest_to_newest 7803 0 mike 2006-01-11 21:55:03 +0000 Section 2.3.4 says: "Another consequence of these rules is that where none of the items in a sequence contributes to the result of an expression, the processor is not obliged to evaluate any part of the sequence. Again, however, the processor cannot dispense with a required cardinality check: if an empty sequence is not permitted in the relevant context, then the processor must ensure that the operand is not an empty sequence." It's not clear quite how much checking this requires. Consider (1,2,3) = (1,2,exactly-one(//title)) //title is not allowed to return an empty sequence. Does this mean we are required to evaluate it and check it? I think we would agree that it does not. In other words, the requirement to do cardinality checking does not cascade. Now consider max((), resolve-uri($collation, 'http://base/')) Does the quoted paragraph mean that I am required to determine that the collation is not (), even though the result of the max() function is clearly (), regardless of the actual collation? It seems to me that the wording of the above paragraph says that this is indeed required. If that's the case, it seems wrong: it's a quite unnecessary constraint on the way the processor operates. Whether the decision is made statically or dynamically, we should always have the freedom to avoid evaluating an expression if its value is not needed. Perhaps we could use a form of words such as: if an expression is evaluated (wholly or in part), then it must be evaluated sufficiently to ensure that any cardinality constraints on the value of the expression are satisfied. Michael Kay 8275 1 chamberl 2006-02-15 21:59:26 +0000 Mike, The Query and XSLT working groups considered your comment during their joint meeting on 01 Feb 2006, and agreed to make editorial changes to Section 2.3.4 (Errors and Optimization) of the XPath and XQuery specifications, clarifying that cardinality checking is required only for expressions that are evaluated, wholly or in part. Since you were present at the discussion, I have marked this issue as Closed. Regards, Don Chamberlin (for the joint working groups)