Data Flow Diagrams

1
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