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Subject: Issue 29 - Proposal For Vote
Issue 29 - Simplification of XPath expressions Proposal: Require that all arguments to BPEL defined XPATH functions must be quoted strings that are statically defined within the XPATH expression. Note: This proposal won't be necessary if we decide to manifest properties as independent XPATH variables since this would let us get rid of getVariableProperty. Rationale: getVariableProperty(getVariableProperty(foo,bar),getVariableProperty(ick,bick)) is completely legal in XPATH. This is a problem because such an expression makes it impossible to statically analyze the expression that contains the function call and determine what variable is being referenced. This is problematic for static analysis of the process because it makes it impossible to determine what variable and property are being accessed so there is no way to check if that variable is accessible from that point in the BPEL process definition or if the variable has the referenced property defined on it. Even worse (in my mind anyway) is that the previous plays havoc with optimizations for compensation handling. If the previous function was contained within a compensation handler then there would be no way to know what variable was being accessed and so the BPEL process would have no choice but to persist all variables visible from the compensation handler, major yuck! We have in the past altered XPATH in order to suit our needs. For example, in some BPEL expressions we have banned the use of the global context node, a node whose presence is actually mandated by the XPATH specification. If we are willing to change XPATH that much I see no reason not to change it here as well. In for a dime, in for a dollar. Section 9.1 - Add a new paragraph after the following paragraph "Any qualified names used within XPath expressions are resolved by using namespace declarations currently in scope in the WS-BPEL document at the location of the expression.": The arguments to all XPATH functions defined in this specification MUST be given as quoted strings. The previous requirement MUST be statically enforced. It is therefore illegal to pass into a BPEL XPATH function any XPATH variables, the output of XPATH functions, a XPATH location path or any other value that is not a quoted string. This means, for example, that getVariableProperty("varA","propB") meets the previous requirement while getVariableProperty($varA,string(getVariableProperty("varB","propB")) does not. Note that the previous requirement institutes a restriction which does not exist in the XPATH standard.
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