title: Property access problems
body: <p>I tried to use this rule:</p>
  
  <pre><code>rule "conformSyncConstraint"
      when
      $syn_con : SyncConstraint(
          $left_stp_period  : leftSTP.period,
          $right_stp_period : rightSTP.period)
      eval( ($left_stp_period.dayOfWeek == $right_stp_period.dayOfWeek &amp;&amp;
          $left_stp_period.dayOrder == $right_stp_period.dayOrder) == false) 
  
      then
      insertLogical(new IntConstraintOccurrence("conformSyncConstraint", 
          ConstraintType.NEGATIVE_HARD,
          1,
                  $syn_con));
  end
  </code></pre>
  
  <p>But I face this error, which seemed a blackbox:</p>
  
  <pre><code>Rule Compilation error : [Rule name='conformSyncConstraint']
      in/co/technovia/timetabler/domain/Rule_conformSyncConstraint_4401252830cd4ee7bc49416ead3da86c.java (8:1459) : The field Period.dayOfWeek is not visible
      in/co/technovia/timetabler/domain/Rule_conformSyncConstraint_4401252830cd4ee7bc49416ead3da86c.java (8:1490) : The field Period.dayOfWeek is not visible
  
  
      at org.drools.planner.config.solver.SolverConfig.buildRuleBase(SolverConfig.java:238)
      at org.drools.planner.config.solver.SolverConfig.buildSolver(SolverConfig.java:170)
      at org.drools.planner.config.XmlSolverConfigurer.buildSolver(XmlSolverConfigurer.java:103)
      at in.co.technovia.timetabler.TimeTableApp.createSolver(TimeTableApp.java:61)
      at in.co.technovia.timetabler.TimeTableApp.main(TimeTableApp.java:45)
  </code></pre>
  
  <p>What is going wrong here?</p>