2631 2006-01-03 14:49:39 +0000 [XPath] Numeric Promotion 2006-02-14 01:22:33 +0000 1 1 1 Unclassified XPath / XQuery / XSLT XPath 2.0 Candidate Recommendation PC Windows XP CLOSED FIXED http://lists.w3.org/Archives/Member/w3c-xsl-query/2005Oct/0039.html P2 normal --- 1 mike chamberl public-qt-comments oldest_to_newest 7577 0 mike 2006-01-03 14:49:40 +0000 This issue was raised on an internal email and is being copied here as a result of action A-278-02. The issue reads: In the Query test suite, test fn-distinct-values-mixed-args-012.xq is: fn:distinct-values((xs:decimal('1.2'), xs:float('1.2'))) and the expected answer is "1.2". This answer is valid if (xs:decimal('1.2') eq xs:float('1.2')). But I'm having trouble deciding from the spec whether these two values are equal. It hinges on the way promotion works. If the decimal is promoted to a float, then the two values are equal. If both values are promoted to doubles, then they are not equal. This is because the float converts to the double 1.2000000476837158. I don't think there is anything in the spec that tells us which way promotion is supposed to work for a value comparison. It's interesting that it makes such a dramatic difference to the result of a simple expression like this. I suspect it's intended that the decimal should be promoted to a float, making these test results correct (and Saxon wrong), but the spec doesn't currently say so. Michael Kay 7579 1 mike 2006-01-03 15:15:42 +0000 Proposal to resolve issue 2631: under action A-278-02 I was asked to propose wording to resolve this issue editorially. The first difficulty is a lack of uniformity in the operator mapping table: numeric operations are handled using a generic type "numeric" than embraces decimal, integer, float, and double, but there is no corresponding generic type for anyURI and string. I think it would be rather disruptive to try and fix that now, so the solution below is a little bit asymmetric. Proposal ======== 1. In 3.5.1 Value Comparisons, add a step 5 as follows: 5. If both the operands are numeric, or if one is of type xs:string and the other of type xs:anyURI, apply type promotion to one of the operands as described in B.1 Type Promotion, so that the two operands have the same primitive type. 2. In Appendix B.2, there is explanatory text for numeric promotion applied to arithmetic operators, but no similar explanation for comparison operators. 2a. Add a new fourth paragraph to B.2: Before looking up an entry in the table below, type promotion is applied to the operands as described in B.1 Type Promotion. 2b. To the paragraph starting "A numeric operator may be validly applied to an operand of type...", add the following: "Where the entry for an operator with numeric operands gives a result type other than numeric (for example idiv, which has a result type of xs:integer, or eq, which has a result type of xs:boolean), then the result is a value of that type, regardless of the types of the operands. For example, the result of comparing an integer to a decimal using the eq operator is a boolean". Michael Kay 7582 2 mike 2006-01-03 17:11:52 +0000 Please note that http://www.w3.org/Bugs/Public/show_bug.cgi?id=2324 is also relevant. 8254 3 chamberl 2006-02-14 01:22:22 +0000 Mike, On 01 Feb. 2006, the Query and XSLT working groups agreed with your suggestion to make editorial changes clarifying the rules for numeric promotion in value comparisons. Since you were present at the discussion, I am marking this Bugzilla entry as closed. Regards, Don Chamberlin