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From "Ingmar Kliche (JIRA)" <j...@apache.org>
Subject [jira] Created: (SCXML-59) <assign location="..." expr="..."> problem for context with different internal XML representation
Date Sun, 23 Sep 2007 18:34:50 GMT
<assign location="..." expr="..."> problem for context with different internal XML representation
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                 Key: SCXML-59
                 URL: https://issues.apache.org/jira/browse/SCXML-59
             Project: Commons SCXML
          Issue Type: Improvement
    Affects Versions: 0.6
            Reporter: Ingmar Kliche


We are currently working on a prototype implementation of a ECMAScript context and evaluator
based on Rhino.

It appears that Rhino has its internal context and uses an internal XML representation different
from org.w3c.dom.node. This means we have to convert every XML Node/Document when it is stored
into the context into Rhino's internal XML representation (e.g. when the datamodel is stored
into the context). This works fine.

The problem occurs with the current implementation of <assign location="..." expr="...">.
Assign uses evalLocation() twice to get two org.w3c.dom.node objects (one for location and
another for expr). Then the implementation of Assign iterates through the two node structures
and stores the expr node under the location node.

Doing this, Assign manipulates a variable within the context from outside, i.e. it manipulates
the XML data tree without using a set() at the context. To do this it makes use of object
references.

For our context this appears to be a problem. As mentioned earlier we have a different internal
XML representation (i.e. other Java classes than org.w3c.dom). Therefore our evalLocation()
returns a org.w3c.dom.node object (as required by the context interface) which is a converted
copy of the internal XML object. Assign therefore works on our copies and as it does not store
the result explicitly back into the context we loose it.

I see the current implementation of Assign therefore as a violation of the context abstraction
(because Assign manipulates data within the context from outside) and propose to change it.
I propose to think about a solution which avoids data convertion (as described above) whereever
possible for evaluators/contexts which use different internal (XML) data representation.

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