CASE STUDY

Check chapter 6

Case Study
The Agricultural Contractors Cooperative
You have been engaged as a System Analyst by the Agricultural Contractors Cooperative (ACC) to assist them in a planned ICT project. This not-for-profit organization’s goal is to help gain work for agricultural contractors. These are people who own and operate specialized equipment such as harvesting equipment, crop storage facilities, transport services and even aircraft for spraying fertilizer and chemicals on crops as well as people with specialized skills such as sheep shearers and crop harvesting and sorting. The ACC provides a telephone service for farmers to call when they need an agricultural contractor. An advantage that ACC offers to Farmers is that they can schedule a sequence of agricultural contractors so that a series of processes can operate more seamlessly such as soil tilling or ploughing followed by seeding; or crop harvesting followed by sorting, storage and transport. Farmers don’t need to buy their own equipment or recruit and manage different teams of workers. ACC has existed for five years and is popular with the agricultural contractors and the farmers who hire them. The telephone service is now very busy and farmers complain that their calls are often not answered. The CEO of ACC believes this all needs to be managed on-line through a web-based booking system for the farmers which would also provide an online diary/appointments system for the agricultural contractors. Farmers could hire agricultural contractors online while the agricultural contractors could accept an assignment, access their schedule online and update the status of their work. They may also make changes or block out times they are unavailable. The CEO of ACC has asked you to investigate high-level requirements and options. You have agreed to undertake the tasks listed as follows.

TASK 1
Draw a context diagram. The context diagram should represent the current information
system at the Agricultural Contractors Cooperative (ACC).
TASK 2
Develop a new level 0 diagram DFD (data flow diagram). The new level 0 diagram DFD should
show the change of the information system at the Agricultural Contractors Cooperative (ACC).
TASK 3
Compare the current information system scenario that presented in TASK 1 and the new
information system scenario that your already presented in TASK 2 to assess the impact of
change and prepare a briefing note for the organizational change management team regarding the anticipated impact of the system

MIS360
System Analysis

Chapter 6: Structuring System Requirements:
Process Modeling

Learning Objectives

Explain process modeling

Discuss data-flow diagramming mechanics,
definitions, and rules

Discuss balancing data-flow diagrams

Discuss the use of data-flow diagrams as analysis
tools

Examine decision tables used to represent process
logic

Process Modeling for Structured Analysis

Process Modeling

• Graphically represents the processes that capture,
manipulate, store, and distribute data between a system
and its environment and among system components.

• Data-flow Diagrams (DFD)
• Graphically illustrate movement of data between external

entities and the processes and data stores within a system

Process Modeling (continued)

• Modeling a System’s Process
• Utilize information gathered during requirements

determination

• Structure of the data is also modeled in addition to the
processes

• Deliverables and Outcomes
• Set of coherent, interrelated data-flow diagrams

Process Modeling (continued)

Deliverables and Outcomes: pg.184

 Set of coherent, interrelated data-flow diagrams
• Context data-flow diagram (DFD): Scope of system.
• Level-O Diagram: Major system’s processes, data

flows, and data stores at a higher level of detail.
• Level-1 diagram: results from

decomposition

of Level-

0 diagram.
• Level-n diagram: it is a DFD diagram that is the result

of n nested decompositions from a process on a level-
0 diagram.

Process Modeling (continued)

Deliverables and Outcomes

 DFDs of current

system

• Enable analysts to understand current system

 DFDs of new logical system
• Technology independent

• Show data flows, structure and functional requirements of new
system

Process Modeling (continued)

• Deliverables and Outcomes (continued)
• Context data-flow diagram (DFD)

• Scope of system

• DFDs of current system
• Enable analysts to understand current system

• DFDs of new logical system
• Technology independent

• Show data flows, structure and functional requirements of new
system

Process Modeling (continued)

• Data-flow Diagramming Mechanics
• Represent both physical and logical information systems,

manual or computer based.

• Four symbols are used
• See Figure 6-3

• Developed by Gane and Sarson

Definitions and Symbols

Definitions and Symbols

Comparison of DeMarco

and Yourdon

and Gane and Sarson

DFD symbol sets

Definitions and Symbols (Cont.)

• Process: works or actions performed on data
(inside the system)

• Data store: data at rest (inside the system)

• Source/sink: external entity that is the origin
or destination of data (outside the system)

• Data flow: arrows depicting movement of
data

Data-Flow Diagramming Mechanics

 Data Flow
• Depicts data that are in motion and moving as a unit

from one place to another in the system

• Drawn as an arrow

• Select a meaningful name to represent the data

Data-Flow Diagramming Mechanics
(continued)
 Data Store

• Depicts data at rest

• May represent data in
• File folder

• Computer-based file

• Notebook

• Drawn as a rectangle with the right vertical line
missing

• Label includes name of the store as well as the
number

Data-Flow Diagramming Mechanics
(continued)
 Process

• Depicts work or actions performed on data so
that they are transformed, stored, or distributed

• Drawn as a rectangle with rounded corners

• Number of process as well as names are
recorded

Data-Flow Diagramming Mechanics
(continued)
 Source/Sink

• Depicts the origin (Source) and/or destination (Sink)
of the data.

• Sometimes referred to as an external entity.

• Drawn as a square symbol.

• Name states what the external agent is.

• Because they are external, many characteristics are
not of interest to us.

Developing DFDs

 Context Diagram
• A data-flow diagram of the scope of an organizational

system that shows the system boundaries, external
entities that interact with the system and the major
information flows between the entities and the system.

Note: only one process symbol, and no data stores shown

Developing DFDs: An Example

• Hoosier Burger’s
Automated Food
Ordering System

Context Diagram
(Figure 6-5)

contains no data
stores

Developing DFDs (continued)

 Level-O Diagram
• A data-flow diagram that represents a system’s major

processes, data flows, and data stores at a higher level
of detail.

• Processes are labeled 1.0, 2.0, etc. These will be
decomposed into more primitive (lower-level) DFDs.

Developing DFDs:
An Example (continued)

– Next step is to expand the context diagram to show
the breakdown of processes (Figure 6-6)

Data-Flow Diagramming Rules

 Basic rules that apply to all DFDs:

• Inputs to a process are always different than

outputs.

– Processes purpose: is to transform inputs into

outputs.

• Objects always have a unique name
– Every process has a unique name.

• In order to keep the diagram uncluttered, you
can repeat data stores and data flows on a
diagram

Data-Flow Diagramming Rules (continued)

 Process
A. No process

can have
only
outputs (a
miracle)

B. No process
can have
only inputs
(black hole)

C. A process
has a verb
phrase label

 Data Store
D. Data cannot be

moved from one
store to another

E. Data cannot move
from an outside
source to a data
store

F. Data cannot move
directly from a data
store to a data sink

G. Data store has a
noun phrase label

 Source/Sink
H. Data cannot move

directly from a
source to a sink

I. A source/sink has a
noun phrase label

Data-Flow Diagramming Rules (continued)

 Data Flow
J. A data flow has only one direction of flow between symbols
K. A fork means that exactly the same data go from a common

location to two or more processes, data stores, or sources/sinks

L. A join means that exactly the same data come from any two or
more different processes, data stores or sources/sinks to a
common location

M. A data flow cannot go directly back to the same process it leaves
N. A data flow to a data store means update
O. A data flow from a data store means retrieve or use
P. A data flow has a noun phrase label

Data Flow Diagramming Rules (Cont.)

Figure 7-6
Incorrect and correct ways to draw DFDs

Decomposition of DFDs

 Functional decomposition
• An iterative process of breaking a system

description down into finer and finer detail.

• Creates a set of charts in which one process on
a given chart is explained in greater detail on
another chart.

• Continues until no subprocess can logically be
broken down any further.

Decomposition of DFDs (Cont.)

 Level-1 diagram results from decomposition of
Level-0 diagram.

 Level-n diagram is a DFD diagram that is the result
of n nested decompositions from a process on a
level-0 diagram.

 Primitive DFD is the lowest level of a DFD.

Level-1 DFD

Processes are labeled 4.1, 4.2, etc.

These can be further decomposed

in more primitive (lower-level)

DFDs if necessary.

Level-1 diagram showing the

decomposition of Process 4.0

from the level-0 diagram for

Hoosier Burger’s food-ordering

system

Level-1 DFD shows

the sub-processes

of one of the

processes in the

Level-0

DFD.

This is a Level-1

DFD for Process

4.0.

Level-n DFD

Processes are labeled

4.3.

1, 4.3.2, etc. If this is the

lowest level of the hierarchy, it is called a primitive DFD.

Level-2 diagram showing the decomposition of

Process 4.3 from the level-1 diagram for Process

4.0 for Hoosier Burger’s food-ordering system
Level-n DFD

shows the sub-

processes of one
of the processes

in the Level n-1

DFD.

This is a Level-2

DFD for Process
4.3.

Balancing DFDs

 When decomposing a DFD, you must conserve inputs to and

outputs from a process at the next level of decomposition

• This is called balancing

 Example: Hoosier Burgers

• In Figure 6-5, notice that there is

• One input to the system:

• the customer order
• Three outputs:

• Customer receipt

• Food order

• Management reports

Balancing DFDs (continued)

• Example (Continued)

• Notice Figure 6-6.

• We have the same inputs and outputs

• No new inputs or outputs have been introduced

• We can say that the context diagram and level-0 DFD
are balanced

Balancing DFDs:
An Unbalanced Example

• In context diagram, we have
one input to the system, A
and one output, B

• Level-0 diagram has one
additional data flow, C

• Therefore. these DFDs are
not balanced

Balancing DFDs

• We can split a data flow into separate data flows on a
lower level diagram

Balancing DFDs:
Four Additional Advanced Rules

Guidelines for Drawing DFDs

1. Completeness
• DFD must include all components necessary for the

system
• Each component must be fully described in the

project dictionary or CASE repository

2. Consistency
• The extent to which information contained on one

level of a set of nested DFDs is also included on other
levels

Guidelines for Drawing DFDs (continued)

3. Timing
• Time is not represented well on DFDs
• Best to draw DFDs as if the system has never started

and will never stop

4. Iterative Development
• Analyst should expect to redraw diagram several

times before reaching the closest approximation to
the system being modeled

5. Primitive DFDs
• Lowest logical level of decomposition
• Decision has to be made when to stop

decomposition

Using DFDs as Analysis Tools

• Gap Analysis
• The process of discovering discrepancies between two or

more sets of data-flow diagrams or discrepancies within a
single DFD

• Inefficiencies in a system can often be identified
through DFDs

Using DFDs in Business Process
Reengineering

• Example: IBM Credit

• Credit approval process is
required six days before
Business Process
Reengineering (see Fig 6-
13)

Using DFDs in Business Process Reengineering
(continued)

After Business Reprocess
Engineering, IBM was

able to process 100 times
the number of

transactions in the same
amount of time

Summary

• Data-flow Diagrams (DFD)
• Symbols

• Rules for creating

• Decomposition

• Balancing

• DFDs for Analysis

• DFDs for Business Process Reengineering (BPR)