Current limitation: Penrose only allows joining one field from one source to another field in another source. 

Ability to use of expression in the join relationship is important for Identity Correlation. 

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Issue dump from jira
$VAR1 = {
          'priority' => '4',
          'customFieldValues' => [],
          'project' => 'PENROSE',
          'status' => '1',
          'components' => [
                            {
                              'name' => 'Engine',
                              'id' => '10009'
                            }
                          ],
          'reporter' => 'jimyang',
          'key' => 'PENROSE-108',
          'assignee' => 'endisd',
          'summary' => 'Support the usage of expression in the join relationship',
          'id' => '10305',
          'updated' => '2008-03-21 10:45:33.0',
          'votes' => '0',
          'fixVersions' => [
                           {
                             'releaseDate' => '2008-09-18 00:00:00.0',
                             'sequence' => '31',
                             'name' => 'Penrose-2.1',
                             'released' => 'false',
                             'id' => '10130',
                             'archived' => 'false'
                           }
                         ],
          'affectsVersions' => [
                               {
                                 'releaseDate' => '2005-10-17 00:00:00.0',
                                 'sequence' => '7',
                                 'name' => 'Penrose-0.9.7',
                                 'released' => 'true',
                                 'id' => '10033',
                                 'archived' => 'false'
                               }
                             ],
          'description' => 'Current limitation: Penrose only allows joining one field from one source to another field in another source. 

Ability to use of expression in the join relationship is important for Identity Correlation. ',
          'created' => '2005-10-27 20:24:54.0',
          'type' => '4'
        };


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