Text Box: This diagram tells a story: Alpha and Beta provide inputs (a and d) respectively) to the information system via processes 1 and 3 respectively.  Process 1 uses a to produce two items of information: b (which is temporarily stored in Data store A) and e (which is sent to process 2).  Process 2 uses data item e and creates information item f for destination "Queue" and stores data item g temporarily in Data Store B.  It cannot do this, of course, until Process 1 has actually produced item e!  Notice that f and g don't have to be the same and certainly neither has to be identical to e Process 3 eventually takes information item c (which of course is in reality some part of or reformatting of item b) and item d and item h and produces data item i as information for destination "Are".  Notice that item i is definitely not going to be available until after items c, d, and h are available, so Process 3 can't finish until both Process 1 and Process 2 have completed.  This is called "logical dependency" and it sets up a hierarchy of timing.  But processes 1, 2, and 3 might begin and operate concurrently.  They just have to finish in a certain order. Notice that the information received by "Queue" and "Are" depends critically on both the original data provided by "Alpha" and "Beta" as well as the correct functioning of Processes 1, 2, and 3.  If there is some problem with the results (i and f), then there is probably some problem with 1, 2, or 3 or the original data a and d so long as we assume that nothing has happened to the data "in transmission" or "in storage" (which is sometimes a technological rather than design) problem.  Link to .ppt Text Box: B Text Box: A Text Box: Queue Text Box: Are Text Box: Alpha Text Box: Beta

Text Box: Data Store Text Box: Data Store Text Box: Sources can also be Destinations Rounded Rectangle: 3 Pro- cess Rounded Rectangle: 2 Pro- cess Rounded Rectangle: 1 Pro- cess

Text Box: No timing or speed is assumed for Data Flows, just direction

Text Box: System Boundary Text Box: i Text Box: h Text Box: g Text Box: f Text Box: e Text Box: d Text Box: c Text Box: b Text Box: a