These represent processes in the system, which handle data. These represent data flows within the system.
Data flows in the direction of the arrow.
Rectangular boxes These represent terminators , or things in the outside world, which provide or receive data. Parallel bars These represent data stores, or places in the system where data may be stored and retrieved at a later time. These represent control processes in the system, which handle events and control other processes. In addition, symbols which have a double border represent off-page pointers, which refer to objects whose context is described more fully in an upper level diagram. This is a method of defin ing the relationship between data objects using a series of shorthand symbols to represent combination, choices and repetition.