need to improve project management module to better management of project and sequensing the tasks

When we create a task for project and give other task as its parent task, which should be done first before completing the task which we have been created, then system should not allowed to complete task which is created before completing its parent task. By this one can manage projects in proper way e.g. one cannot build a house before completing its base. This is not happening at present in the system and any task can be done at any time.