Keng Siau Department of Management University of Nebraska - Lincoln Data Flow Diagrams Keng Siau Department of Management University of Nebraska - Lincoln

Common Errors in DFDs Forgetting to include a data flow or pointing an arrowhead in the wrong direction Connecting data stores and external entities directly to each other Incorrectly labeling processes and/or data flow

Common Errors in DFDs Including more than nine processes on a DFD (not recommended) Omitting data flow Creating unbalanced decomposition in child diagram each child diagram should have the same input and output data flow as the parent process exception: minor output such as error lines

Logical vs. Physical DFDs DFDs are categorized as either logical physical Logical DFDs not concerned about how the system is or will be constructed Physical DFDs show how the system is or will be constructed

Progression of Models Current Logical DFD New Logical DFD New Physical DFD

Advantages of Logical DFDs Better communication with users More stable systems Better understanding of the business by analysts Flexibility and maintenance Elimination of redundancies and easier creation of the physical model

Advantages of Physical DFDs Clarifying which processes are manual and which are automated Describing processes in more detail than logical DFDs Sequencing processes that have to be done in a particular order Identifying temporary data stores Specifying actual names of files and printouts Adding controls to ensure the processes are done properly

Partitioning DFDs The process of analyzing a DFD and deriving a series of manual procedures and computer programs A dashed line is drawn around a group of processes that are included in each computer program or manual procedure

Why Partition ? Different user groups should have different programs Processes that execute at different time must be in separate programs Similar tasks may be included in the same program Several batch processes may be included in the same program for efficiency

Why Partition ? Several processes may be included in the same program or job stream for consistency of data Processes may be separated into different programs for security

Purposes of DFDs Unexploded DFDs are useful to identify information requirements Exploded DFDs can be used for presentation education gathering feedback information from users

Uses of DFDs Used to analyze the system to ensure that the design is complete Used to partition the system into programs Used for system documentation