1208 2005-04-05 09:09:51 +0000 [F&O] deep-equal() is not transitive and reflexive 2005-09-29 10:39:12 +0000 1 1 1 Unclassified XPath / XQuery / XSLT Functions and Operators 1.0 Last Call drafts PC Windows XP CLOSED FIXED P2 normal --- 1 mike ashok.malhotra public-qt-comments oldest_to_newest 3800 0 mike 2005-04-05 09:09:51 +0000 The deep-equal() function as currently defined is not transitive and it is not reflexive (it does not guaranteed that deep-equal($A, $A) is true). The known problems are as follows: A. The transitivity problem arises from the condition that two elements are deep-equal if (among other things): # One of the following conditions holds: * Both element nodes have a type annotation that is either a simple type or a complex type with simple content, and the typed value of $i1 is deep-equal to the typed value of $i2. * One or both of the element nodes has a type annotation that is neither a simple type nor a complex type with simple content, and the sequence $i1/(*|text()) is deep-equal to the sequence $i2/(*|text()). This means that given X: <a>1</a> of type xs:integer Y: <a>1.0</a> of type xs:decimal Z: <a>1</a> of type xs:anyType we have X=Y, X=Z, and Y!=Z. B. The function is not reflexive because of the possibility of NaN values. If $X is a document that contains a typed NaN value at any depth, then deep-equal($X, $X) is false. C. The lack of support for comparison of durations also leads to a problem. If $X is a document that contains a typed xs:duration value at any depth, then deep-equal($X, $X) is false. The effect of these problems is that deep-equal is difficult for an optimizer to handle, for example if it is used as a join condition then it's not possible to support it using a hash join. It also means that the function is not suitable to underpin future developments that introduce a grouping capability or a deep-distinct() function. There are several things we could do about the problem: Option 1: scrap the function Option 2: live with its deficiencies Option 3: fix the problems 3A. Specify that two elements can be deep-equal only if they are both annotated as having complex content or both annotated as having simple content. 3B. Specify that for the purposes of deep-equal, NaN is equal to NaN. (We already have this rule for distinct-values()) 3C. Specify an equality comparison for xs:duration values. Unlike ordering, there is no good reason for this to be unsupported. Any duration can be simply and unambiguously represented as the sum of a dayTimeDuration and a yearMonthDuration and we simply specify that two durations are equal if these two components are equal. Michael Kay 3091 1 ashok.malhotra 2005-05-26 20:54:40 +0000 The joint WGs decided on 5/17/2005 to close this bug by accepting Michael Kay's recommendations. Ashok Malhotra requested clarification on 3A which were provided by Michael Kay and Henry Thompson in (member-only) messages: http://lists.w3.org/Archives/Member/w3c-xsl-query/2005May/0079.html and http://lists.w3.org/Archives/Member/w3c-xsl-query/2005May/0080.html