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

2. 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

3. 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

4. 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

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

6. 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

7. 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

8. 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

9. 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

10. 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

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

12. 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