1128 2005-02-22 15:21:27 +0000 Accessing and modifying members of lists and arrays 2005-09-28 22:17:11 +0000 1 1 1 Unclassified WS Choreography Last Call Comment: Confirmed Closed unspecified PC Linux CLOSED WONTFIX http://www.w3.org/TR/2004/WD-ws-cdl-10-20041217/ P2 normal -- 1166 1 gritzinger steve martin.chapman oldest_to_newest 4070 0 gritzinger 2005-02-22 15:21:28 +0000 Due to a lack of clarity in existing XML specifications, the WS-Choreography Working Group is unable at this time to recommend an approach for accessing and modifying members of lists and arrays. 3889 1 gritzinger 2005-03-09 15:18:43 +0000 Proposal from Gary Brown: http://lists.w3.org/Archives/Public/public-ws-chor/2005Mar/0013.html Following on from Tony's ideas: List/Array Access/Update issue Date: 9th March 2005 Accessing a list or array This can be achieved using existing XPath expression support. The CDL 'getVariable' function will return the value associated with a variable and optionally a component within the XML document represented by the variable. It would then be possible for the XPath expression to perform further evaluation on the returned result. Alternatively the list accessor could be placed in the XPath expression supplied as a parameter to the 'getVariable' function. For example, if we have a variable called 'doc' which contains the XML data from Tony's previous example, then variable 'doc' will contain: <listA> <listItem>1</listItem> <listItem>2</listItem> <listItem>4</listItem> <listItem>8</listItem> </listA> If we also have a variable 'index' that is acting as an index value, so is of type xs:integer, then the following Xpath expression would be used to access the list element associated with the current index value, cdl:getVariable('doc', '', "/listA/listItem[cdl:getVariable('index','','','')]", '') Alternatively, we could move the list accessing expression outside the function: cdl:getVariable('doc','')/listA/listItem[cdl:getVariable('index','','')] This may be a better approach than embedding the XPath expression inside the 'getVariable' function, which avoids nested functions. It may be even better to be able to reference CDL variables natively within the XPath expression, although this would not cater for multi-part messages - and other 'isVariableAvailable' function would still be required. Modifying a list or array I don't think it is appropriate to add functions to XPath that modify the document being queried, as this may have unknown consequences on the remainder of the xpath evaluation. My preference would be to use XPath expressions to identify the context for the modification being performed, and then have specific activities to perform the modification. One possibility would be to change the current assign/copy construct, so that copy would be a 'replace' operator, while 'insert'/'delete'/'append' operators could be used for list manipulation. For example, <update> <!-- instead of 'assign' --> <copy target="cdl:getVariable('newNode')" expression=" '<listItem>16</listItem>' " /> <append context="cdl:getVariable('doc')/listA" expression="cdl:getVariable('newNode')" /> <delete expression="cdl:getVariable('doc')/listA/listItem[2]" /> </update> The 'insert' could be the same syntax as the append, with the addition of a 'position' attribute to indicate the insertion point. If it is considered necessary to separate the variable from the context node within the variable's document, then that could be easily achieved. For example, <append variable="cdl:getVariable('doc')" context="/listA" expression="cdl:getVariable('newNode')" /> NOTE: To support concurrent update of any information (but especially the lists), within a choreography, we should stipulate that the 'update' activity is atomic and isolated. 3256 2 steve 2005-05-16 14:01:41 +0000 PROPOSAL TO CLOSE WON'T FIX and add text to primer Basis: To properly modify information (lists/arrays/xml documents) in concurrent threads requires a level of isolation/synchronization, and CDL only provides a coarse mechanism for this - so would prefer to leave these modifications for ***silentActions***, which can then implement any necessary synchronization. We should not really be adding further activities that make this a more turing complete language. Thus silentActions can be used as a suitable silent mechanism for accessing and modifying lists and arrays and therefore we do not need explicit support in WS-CDL to do this. The primer should include an example of how this might be done using WS-CDL, silentActions and a suitable end point language. -DONE BY SRT 3258 3 steve 2005-05-16 14:15:27 +0000 Changed QA Contact to steve from martin as steve is main author of primer and this has been reassigned as a primer issue