boost::shared_ptr<ModelAPI_Data> aData = feature()->data();
boost::shared_ptr<ModelAPI_AttributeRefAttr> anAttr =
boost::dynamic_pointer_cast<ModelAPI_AttributeRefAttr>(aData->attribute(CONSTRAINT_ATTR_ENTITY_A));
boost::shared_ptr<ModelAPI_Data> aData = feature()->data();
boost::shared_ptr<ModelAPI_AttributeRefAttr> anAttr =
boost::dynamic_pointer_cast<ModelAPI_AttributeRefAttr>(aData->attribute(CONSTRAINT_ATTR_ENTITY_A));