title: Optaplanner - How to model a timeslot pattern scheduling problem if certain type of tasks require less resource when they're scheduled in same slot?
body: <p>I'm developing a daily timeslot pattern scheduling problem with task precedence and daily shifts resource constaint.</p>
  <ul>
  <li>Each product has several batches and each batch consists of sequential tasks (like prepare\mix\process etc.) to be scheduled.</li>
  <li>Tasks consume shift units and there are daily shift limits for each type of tasks.</li>
  <li>If two prepare tasks of same product are schedued on the same day, they consume 1 units of shift together, while each of them still use 1 shift unit if they are scheduled apart.</li>
  <li>Succeeding tasks (like mix or process) of same products won't benefit from scheduling together on the same day. If one mix task use 1 shift unit, then two mix tasks scheduled on the same day would consume 2 shift unit in total.</li>
  </ul>
  <p>This senario differs from project job scheduling problem, where task durations variation depend on machines, not other tasks.</p>
  <p>I've implemented a simple model without changeable resource requirement and it works. I came up with a dummy idea: manually combine each two prepare tasks together and consider it as one task. But this would make the model less versatile and harder to write drool rules.</p>
  <p>Any hint or help is appreciated. Thanks.</p>