This document defines and provides examples of various modeling techniques used in systems analysis and design: 1) Data Flow Diagrams (DFDs) visually represent the flow of data through a system and its processes, data stores, external entities, and levels of abstraction. 2) Decision tables organize the conditions and expected outcomes of decision logic in a matrix format. 3) Decision charts use a tree structure to model decisions, consequences, probabilities, costs, and utilities. 4) Structure charts describe the hierarchical modular structure and relationships between functions, subfunctions, modules, and control logic (conditions, loops, data coupling) within a system or computer program.

1. DFD, Decision Table, Decision Chart,
Structure Charts

2. DFD(Data flow Diagram)
• Data flow diagram is a graphical representation of data flow
through a information system.
• DFDs used for visualization of data processing, shows what
kinds of information will be input and output from the
system.
• DFD shows where the data will come from and go to, and
where the data will be stored.
• Example -

3. DFD
• Process
Transform of incoming data flow(s) to
outgoing flow(s).
• Data Flow
Movement of data in the system.
• Data Store
Data repositories for data that are
not moving. It may be as simple as a
buffer or a queue or a s sophisticated
as a relational database.
• External Entity
Sources of destinations outside the
specified system boundary.

4. Levels of DFD
• The DFD may be used for any level of data
abstraction. DFD can be partitioned into
levels. Each level has more information flow
and data functional details than the previous
level.
• Like level 0 DFD
level 1 DFD.

5. DFD

6. Decision Table
Combinations • A decision table lists
Causes Values 1 2 3 4 5 6 7 8
Cause 1 Y, N Y Y Y Y N N N N
Cause 2 Y, N Y Y N N Y Y N N
Cause 3 Y, N Y N Y N Y N Y N
Effects
Effect 1 X X X
Effect 2 X X X
causes and effects in a
matrix. Each column
represents a unique
combination.
• Purpose is to structure
logic.
• Cause = condition,
Effect = action = expected
results

7. Structure of Decision Table
The four quadrants
Conditions Condition alternatives
Actions Action entries

9. Decision Chart
• A decision chart is a decision support tool that uses a
graph or model of decisions and their possible
consequences, including chance event outcomes,
resource costs, and utility.
• Every decision chart begins with what is termed a
root node, considered to be the "parent" of every
other node. Each node in the tree evaluates an
attribute in the data and determines which path it
should follow.
• Decision chart helps for analysis the data.

10. Example

11. Structure Chart
• Describe functions and sub-functions of each part
of system (in more detail than a DFD)
• Show relationships between common and unique
modules of a computer program
• Hierarchical, Modular structure
– Each layer in a program performs specific activities
– Each module performs a specific function

12. Steps in drawing a structure chart
• Review the DFDs and object models
• Identify modules and relationships
• Add couples, loops, and conditions
• Analyze the structure chart, the DFDs, and the
data dictionary

13. Structure Chart
Structure Chart symbols
represent
• Modules
(sequential logic)
• Conditions (decision logic)
• Loops
(iterative logic)
• Data couples
• Control couples
• Rectangle represents a
module (program or
subroutine)
• Control Modules
(mainline) branch to sub-modules
• Library modules are
reusable and can be
invoked from more than
one Control Module
elsewhere in the system.

14. Structure Chart

15. Structure Chart - Condition
• A line with a diamond
• Indicates that a control module determines
which subordinate module will be invoked.

16. Structure Chart for
Calculate Pay Amount Routine

17. Structure Chart for Entire
Calculate Payroll Program

18. Summary - Structure Charts
– Show the relationships among program modules
– Structure Chart consists of:
• Modules - Related program code organized into small units
that are easy to understand and maintain
• Data couples - Data passed between modules
• Control couples - Data passed between modules that
indicates a condition or action to another module (e.g. End
of File)
• Conditions - determines what subordinate module a control
module will run
• Loops - Indicates one or more subordinate modules are
repeated
– Structure Charts are based on the DFD and Data Dictionary