def __init__(self) :
self.properties = PropertyTable()
self.property_types = dict() # name -> Property
self.inv_property_types = dict() # Property -> name
self.modified_properties = dict()
self.game_defined = False
self.relations = dict()
self.relation_handlers = []
self.name_to_relation = dict()
self._activities = dict()
self.activity = ActivityHelperObject(self)
