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Subject: Re: [xacml] [CR] 0047:Function specification for XPath handler
Polar, I should have written node comparisons (is or isnot) not op:node-equal. Node comparison is described in http://www.w3.org/TR/xpath20/, Section 3.5.3: In the definition of the node identity in XPath data model (http://www.w3.org/TR/query-datamodel/), function node-equal is used. It is a little complicated, but I meant that semantics. I don't mean deep-equal here. ==== 3.5.3 Node Comparisons (is or isnot) The result of a node comparison is defined by applying the following rules, in order: 1.Each operand must be either a single node or an empty sequence; otherwise a dynamic error is raised. 2.If either operand is an empty sequence, the result of the comparison is an empty sequence. 3.A comparison with the is operator is true if the two operands are nodes that have the same identity; otherwise it is false. A comparison with the isnot operator is true if the two operands are nodes that have different identities; otherwise it is false. See [XQuery 1.0 and XPath 2.0 Data Model] for a discussion of node identity. Use of the is operator is illustrated below. The following comparison is true only if the left and right sides each evaluate to exactly the same single node: //book[isbn="1558604820"] is //book[call="QA76.9 C3845"] ==== So in our case, (xpath-equal "//md:patient[md:first='Alice']/ "//md:patient[md:last ='Johnson']") shall return true if both xpath returns the identical node, <md:patient>. <md:patient> <md:first>Alice</md:first> <md:last>Johnson</md:last> </md:patient> Does it make sense? Michiharu Kudo IBM Tokyo Research Laboratory, Internet Technology Tel. +81 (46) 215-4642 Fax +81 (46) 273-7428 Polar Humenn <polar@syr.edu> To: Michiharu Kudoh/Japan/IBM@IBMJP cc: XACML <xacml@lists.oasis-open.org> 2002/09/20 04:39 Subject: Re: [xacml] [CR] 0047:Function specification for XPath handler Michiharu, You have refered me to "op:node-equal" for your desired fucntion "xacml:xpath-equal". This specification states that two nodes are equal in this sense if they have the same identity. I'm confused on this notion of node identity. So, hopefully you can resolve my confusion. It appears that the name of a node is its fully qualified path by its element names (I think). In your example you have <Apply FunctionId="function:xpath-equal"> <AttributeValue>/Request/Subject/Attribute[@AttributeId ="role"]/AttributeValue </AttributeValue> <AttributeValue>/Request/Subject/Attribute[@AttributeId ="role"]/AttributeValue </AttributeValue> </Apply> Noting that the two XPATH expressions are the same, and let's say the particular "role" attribute of the request context contains "Doctor" are you comparing: 1. "/Request/Subject/Attribute/AttributeValue" to "/Request/Subject/Attribute/AttributeValue", or 2. "Doctor" to "Doctor" The semantics in the: > http://www.w3.org/TR/xquery-operators/ > Please see section 13.1.6 seems to suggest that 1 is the case. Are you really looking to use "op:deep-equal"? If you mean op:node-equal you must pick out the same node by name. This really means that we are really only comparing their XPATH expressions to see if they correspond. (xpath-equal "//md:record/*" "//md:record/name") would always be true, regardless, because although the "//md:record/*" can match any //md:record/FavoriteElementNameHere. I'm just confused. Help! -Polar
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