             # described in the extendModeling and extendSession
             # functions below.
             extendSessions = ->
-              # Adds the following modeling parameter result
-              # properties:
+              # Adds the following modeling label map properties:
+              # * parameterResult - the parent parameter result object
+              # * key - the parent parameterResult key
+              #
+              # @param labelMap the object to extend
+              # @param paramResult the parent parameter result
+              extendLabelMap = (labelMap, paramResult) ->
+                labelMap.parameterResult = paramResult
+                Object.defineProperty labelMap, 'key',
+                  get: ->
+                    @parameterResult.key
+              # Adds the following modeling parameter result properties:
               # * key - the parameter result access property name
               # * modelingResult - the parent modeling result
               #   reference 

                # Extend the modeling result object.
                extendModelingResult(modeling.result, modeling)
                # The modeling overlays property returns the label maps
                # which have a color table.
                Object.defineProperty modeling, 'overlays',
                  get: ->
                    (res.overlay for res in _.values(@result) when res.overlay?)
                
              # Fixes the session acquisition date and adds the following
              # session properties:
              # * number - the one-based session number in acquisition order
              # * subject - the session parent subject reference
              # * overlays - the label map objects with a color table
              extendSession = (session, number) ->
                # Set the session subject property.
                session.subject = subject

                # Add the modeling properties.
                for modeling in session.modelings
                  extendModeling(modeling, session)
                # The session overlays property.
                Object.defineProperty session, 'overlays',
                  get: ->
                    associate = (accum, modeling) ->
                      accum[modeling.protocol] = modeling.overlays
                    modelings = (mdl for mdl in @modelings when mdl.overlays.length?)
                    if modelings.length?
                      _.reduce(modelings, associate, {})
              
              # Extend each session.
              for session, i in subject.sessions
