The writer is not disturbed by the read action. The communication is synchronous. A state vector connection is represented by a diamond connected to the reader by an arrow and to the writer by an undirected line. The direction of the arrow represents the direction of data flow. The circle is connected to a reader and a writer, where an arrow is used to indicate the direction of data flow.
Communication is synchronous and takes place on the initiative of the reader.
An SND of the robot controller of figure C.20 . Figure C.22 shows an SND of the robot controller of figure C.20 . All rectangles represent software entities. External entities are not shown.