From: Kay, Michael <Michael.Kay@softwareag.com>

Date: Tue, 10 Jun 2003 17:49:29 +0200

Message-ID: <DFF2AC9E3583D511A21F0008C7E62106073DCEF3@daemsg02.software-ag.de>

To: public-qt-comments@w3.org

Date: Tue, 10 Jun 2003 17:49:29 +0200

Message-ID: <DFF2AC9E3583D511A21F0008C7E62106073DCEF3@daemsg02.software-ag.de>

To: public-qt-comments@w3.org

Software AG believes that the size of the function library defined in the Functions and Operators document is too large. The size of the library directly affects the cost of implementation, which experience shows is the major factor determining the success or failure of a proposed standard. It also affects the cost of learning to use the language, which is another important predictor of success. It is clearly proving difficult for the working group to debug the specification completely: reducing the number of functions will greatly assist this task. Between CR and final Recommendation the working groups will be required to demonstrate interoperability of implementations. A large function library greatly increases the difficulty of this task, and means it will take longer to get to Recommendation status. Again, any further delays in getting the specifications finished reduces the chance that they will succeed in the market. Giving users several ways to express the same thing makes it much more difficult for optimizers to detect common coding patterns and optimize them. A large function library therefore reduces the chance that common constructs will be well optimized. Software AG proposes a number of simplifications to the function library. This message considers the general-purpose functions. A second message will address the functions concerned with handling of dates, times, and durations. Proposal: remove the following functions A1. fn:context-item() This is a trivial synonym for ".". No-one is likely to use it. A2. fn:current-date() and fn:current-time() These can be trivially derived from fn:current-dateTime() A3. fn:deep-equal() This is semantically complex and unlikely to meet everyone's needs for comparing equality. Users can write their own version to match their own needs. The use of deep-equal() in distinct-values() can be replaced by making distinct-values a (higher-order) operator instead of a function: EXPR "with" "distinct" EXPR ("," EXPR )* A4. fn:distinct-nodes() This is likely to be needed very rarely and can be trivially written as $x/. A5. fn:empty() This is trivial syntactic sugar for count($x)=0, or not($x). The name is also misleading, since other XML specifications use the word "empty" to mean "having no children": users will make the mistake of thinking that empty(E) is true if E is an element with no children. A6. fn:ends-with() The effect of this function can be readily achieved using the fn:matches() function with a regular expression. A7. fn:exists() This is trivial syntactic sugar for count($x)!=0, or boolean($x). A8. fn:index-of() This is a rarely-needed function, and index-of($s, $v) can be readily rewritten as for $i in 1 to count($s) return if ($s[$i] eq $v) then $i else () A9. fn:insert-before() The most common requirement is to insert at the start or the end, which can be achieved using the "," operator. The rare requirement to insert in the middle can be achieved using ($target[position() lt $position], $inserts, $target[position() ge $position]) A10. fn:item-at() The effect of this function can be easily achieved using a numeric predicate. A11. fn:node-kind() It is easy to test the kind of a node using "instance of" (or "type switch" in XQuery) A12. fn:remove() The effect of this function can be readily achieved by writing $target[position() ne $n] A13. fn:sequence-node-identical() This function is very rarely required; if it is ever needed, it can be written as every $i in 1 to max(count($arg1), count($arg2)) satisfies ($arg1[$i] is $arg2[$i]) A14. fn:string-pad() This function can be readily written as string-join(for $i in (1 to $padCount) return $padString, "") A15. fn:subsequence() Both variants of this function can be readily written using positional predicates: $sourceSeq[position() ge $startLoc] $sourceSeq[position() ge $startLoc and position() lt $startloc + $length] Michael Kay Software AGReceived on Tuesday, 10 June 2003 11:49:44 UTC

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