Issue - 103 - Standardizing $varName syntax for XPath to refer to a BPEL variable

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Issue - 103 - Standardizing $varName syntax for XPath to refer to a BPEL variable

Status: open
Date added: 9 Mar 2004
Submitter: Alex Yiu
Date submitted: 08 March 2004
Description:

Right now, there are three BPWS functions defined in BPEL can be called in an XPath Query / Expression.

bpws:getVariableProperty ('variableName', 'propertyName')
bpws:getVariableData ('variableName', 'partName'?, 'locationPath'?)
bpws:getLinkStatus('linkName')
For refering to a variable data, if data is of an XSD complex type or 
XSD simple type (not WSDL 1.1 type), we want to add one more way to refer to a 
variable on top of getVariableData() Function Call? That is using "$varName" 
syntax. 

Currently, we have:
"bpws:getVariableData(orderDetails) > 100"
The additional way will 
look like: 
"$orderDetails > 100"
Note that:

• the additional syntax already got standardized in XPath 1.0 (also in XPath 2.0 and XQuery spec) for a while. Its semantics and syntax are very stable and clear to existing XPath users
  
• Its advantages:
  • simpler, less typing
    
  • easier and better static analysis analysis in XPath: a variable reference can have a more specific type, instead of a generic getVariableData() which essentially returns xsd:any
  • Any static analysis performed on bpws:getVariableData() actually is anti-intuitive to or even does not fit well with the XPath or XQuery function call model. For one function, there should be one designated returned type. Static analysis that requires the returned types changing on the fly tends to be hacky.
  • Note: One can apply XPath directly to a variable. E.g.: "$var/some/xpath/here"

References: 
http://www.w3.org/TR/xpath#NT-FunctionCall
http://www.w3.org/TR/xpath#NT-VariableReference
Changes: 9 Mar 2004 - new issue

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