Flowcharting and Data Flow Diagrams

1
Flowcharting and Data Flow Diagrams

• Supplemental Chapter A

2
Objectives

• The objective of this supplement is to introduce
  you to two types of documentation tools
• Flowcharts and
• Data Flow Diagrams
• You should be able to
• Understand and prepare flowcharts describing the
  information system and procedures used in the
  system
• Understand and prepare data flow diagrams
  depicting the logic of the system

3
Purpose and Description of Flowcharts

• Graphically document information systems
• Summarize pages of narrative
• Focus on the physical aspects of information flows

• Types of flowcharts
• System flowcharts show the entire system
  configuration, including documents, data
  flows, and processes
• Document/Procedure flowcharts show the creation,
  flow, and destinations of documents and the
  procedures performed on them
• Hardware flowcharts show the hardware
  configuration
• Program flowcharts show the logic and processing
  steps of a computer program

4
Basic Elements of System/Document Flowcharts

• May draw freehand or with a template
• Software packages - Visio, PowerPoint, Designer
• Three simple graphical elements may be combined
  to represent various types of physical
  information flows and processes
• Symbols Flow lines Areas of responsibility

Cashier
Dept A
Bank
5
Document Flow in a Manual System
Employee involved
Accounting department
in the transaction
Record transaction journal entry
Transaction Journal
Start
General Ledger
Prepare source document
Post Journal entries to sub.ledger
Adjust and close ledger
Prepare financial statements
Recorded document
3
Source Document
1
2
3
Financial Statements
Trial Balance
Subsidiary Ledger
N
Investors/ Creditors
N numeric
N
6
Sales/Collection Document Flowchart
N numeric
7
Flowchart Symbols Documents
8
Flowchart Symbols
9
Flowchart Symbols
10
Flowchart Element 2 Flow Lines

• Flow lines are used to connect the symbols on the
  document flow chart.
• A solid line indicates the flow of a document or
  object
• A dotted or dashed symbol indicates a flow of
  information rather than the physical document
• Arrows are used when the documents or information
  flow is not left-to-right or top-to-bottom
• Some flowcharts also show communication flows
  such as by telephone modem or satellite

11
Flowcharting Element 3 Area of Responsibility

• Areas of responsibility are displayed to enable
  the flowchart reader to clearly identify changes
  in responsibility as the documents flow through
  the system.
• They are represented on flowcharts by segmenting
  and labeling columns.
• Areas of responsibility may be departments,
  sections within a department, or individual
  employees within a department.
• Judgment must be used in choosing the level of
  subdivision that one column should represent.

12
Preparation Conventions

• Left-to-right, Top-to-bottom
• All documents must have an origin and termination
• indicate origin by darkening one corner of the
  symbol
• each copy of the document must flow to
• a permanent file symbol
• a symbol denoting an exit from the system, or
• an off-page connector
• a document destruction symbol (small black box)
• cradle to grave documentation

• Keep flowcharts uncluttered
• place areas with frequent interchange in adjacent
  columns
• enter narrative only in symbols
• Make sure progress of a document is clear.
  Diagram a document
• before and after each process
• entering or leaving a file
• entering or leaving a page or area of
  responsibility
• Make sure the flowchart is complete

13
The Basic Elements of Hardware and System
Flowcharts

• Program flowcharts depict the detailed logic of a
  computer program.
• Only five symbols are used in program
  flowcharting
• Input/Output (see C on Exhibit A-4),
• Process (see E on Exhibit A-4),
• Decision (see F on Exhibit A-5),
• Start/End (see B on Exhibit A-5), and
• Flow lines (see I on Exhibit A-5).
• As always, a description of the logic is
  recorded on the face of the symbol.

• Hardware flowcharts show the hardware
  configuration of a system.
• The same symbols are used, but they are used to
  represent physical pieces of computer hardware.
• the document symbol - printer,
• the magnetic tape symbol - tape drive,
• a disk symbol - disk drive,
• a computer process symbol - central processor,
  and
• an off-line process symbol - auxiliary hardware
  like an optical character reader.
• The type of hardware is recorded on the face of
  the symbol.

14
Summary

• The flowchart is one of the easier types of
  documentation for information customers and
  management to understand.
• Often, auditors use system, document, and
  procedure flowcharts to understand business and
  systems controls in an environment

• The primary weakness of the flowchart is that it
  is tied to physical information flows and system
  characteristics that hide the procedural essence
  of the system.
• Some flowcharts are full of data and processing
  artifacts because they are tied to an outdated
  information technology.

15
Data Flow Diagrams (DFD)

• Data flow diagramming symbols are used for a
  variety of system analysis purposes, including
  graphically displaying the logical flows of data
  through a process.
• Unlike flowcharts which represent the physical
  components of an information system, data flow
  diagrams can provide a more conceptual,
  nonphysical display of the movement of data
  through a system.
• Data flow diagrams disregard such things as
  organizational units, the computer on which the
  data are processed, and the media on which the
  data are stored.
• The movement of data across offices or
  departments within a particular system
  environment are not represented.

16
Data Flow Diagrams (DFD)

• There are different categories of data flow
  diagrams
• Data flow diagrams of the current physical system
• Data flow diagrams of the current logical system
• Data flow diagrams of the new or proposed logical
  system
• Data flow diagrams of the new proposed physical
  system

• Both logical and physical diagrams use the same
  set of symbols.
• The logical diagrams show the conceptual flow of
  data without including any references to the
  physical characteristics of the system.
• The physical diagrams, on the other hand, include
  labels that describe physical attributes of the
  system, such as labeling worker or job titles,
  department names, and the names or descriptions
  of the technology used to process and store the
  data.

17
Data Flow Diagram Symbols
18
Data Flow Diagram Symbols

• Process
• Circles are used to represent processes that take
  data inflows and transform them to information
  outflows.
• The circle contains two labels.
• The first label is a process number (explained
  later) and the second is a process name.
• Some use rectangular boxes with rounded corners.

19
Data Flow Diagram Symbols

• Data Sources and Sinks
• Rectangles (or squares) represent data (inflow)
  sources and (information outflow) sinks
• The rectangle is labeled with the name of the
  data source or sink/destination (e.g. Customer,
  Vendors, Government Agency).
• The sources and sinks play an important role in
  the data flow diagram.
• The sources and sinks are agents external to
  (i.e. outside the scope of) the system
  represented on the diagram.
• They delineate the boundaries of the system.

(B) Data inflow sources, information outflow
destinations
20
Data Flow Diagram Symbols

• Data Flow Lines
• Data flow lines display the route of data inflow
  and information outflow.
• They can be straight or curved lines.
• The data flow is generally labeled with the name
  of the data (e.g. a customer order, a bill, a
  financial analysis) and the arrow indicates the
  direction of the data flow.

21
Data Flow Diagram Symbols

• Data Stores
• Two parallel straight lines are used to display a
  store or collection of data.
• Some people refer to data stores as data at rest.
  
• A description of the data store contents is
  entered on the symbol.
• Data stores are used anytime it is necessary to
  store the output from a process before sending it
  on to the next process.
• Some use a rectangular box that is open at one
  end.

Inventory
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Constraints General Rules

• All processes should have unique names. If two
  data flow lines (or data stores) have the same
  label, they should both refer to the exact same
  data flow (or data store).
• The inputs to a process should differ from the
  outputs of a process.
• Any single DFD should not have more than about
  seven processes.

23
Constraints Process Rules
Incorrect

• No process can have only outputs. (This would
  imply that the process is making information from
  nothing.) If an object has only outputs, then it
  must be a source.
• No process can have only inputs. (This is
  referred to as a black hole.) If an object has
  only inputs, then it must be a sink.
• A process has a verb phrase label.

Correct
Incorrect
Correct
Edit
24
Constraints Data Store

• Data cannot move directly from one data store to
  another data store. Data must be moved by a
  process.
• Data cannot move directly from an outside source
  to a data store. Data must be moved by a process
  that receives data from the source and places the
  data in the data store.
• Data cannot move directly to an outside sink from
  a data store. Data must be moved by a process.
• A data store has a noun phrase label.

No
No
Yes
No
Yes
CUSTOMER
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Constraints Source/Sink

• 11. Data cannot move directly from a source to a
  sink. It must be moved by a process if the data
  are of any concern to the system. If data flows
  directly from a source to a sink (and does not
  involved processing) then it is outside the scope
  of the system and is not shown on the system data
  flow diagram DFD.
• 12. A source/sink has a noun phrase label.

Incorrect
Correct
Customer
26
Constraints Data Flow

• 13. A data flow has only one direction between
  symbols. It may flow in both directions between
  a process and a data store to show a read before
  an update. To effectively show a read before an
  update, draw two separate arrows because the two
  steps (reading and updating) occur at separate
  times.
• 14. A fork in a data flow means that exactly the
  same data goes from a common location to two or
  more different processes, data stores, or
  sources/sinks. (This usually indicates different
  copies of the same data going to different
  locations.)

No
Yes
A
No
B
A
Yes
A
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Constraints Data Flow

• 15.A join in a data flow means that exactly the
  same data comes from any of two or more different
  processes, data stores, or sources/sinks, to a
  common location.
• 16.A data flow cannot go directly back to the
  same process it leaves. There must be at least
  one other process that handles the data flow,
  produces some other data flow, and returns the
  original data flow to the originating process.

• 17.A data flow to a data store means update
  (i.e., delete, add, or change).
• 18.A data flow from a data store means retrieve
  or use.
• 19.A data flow has a noun phrase label. More
  than one data flow noun phrase can appear on a
  single arrow as long as all of the flows on the
  same arrow move together as one package.

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Context Level Diagram Events Driven System
The highest level of data flow diagrams is the
context diagram. A single system is represented
on a context diagram and it provides the scope of
the system being represented identified in a
process symbol in the center of the diagram
labeled with a 0. The context diagram shows one
process (representing the entire system) and the
sources/sinks that represent the boundaries of
the system. The data flow lines into the process
represent the input data to the system (provided
by sources) and the data flow lines from the
process represent the output information from the
system (going to the sinks).
External Events
Customers
Management
Reports
0Events Driven System
Investors and Creditors
Internal Departments
Financial Statements
Internal Events
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Event Driven Design - Level Zero System Processes
(Data Flow Diagram)
Internal events
Record process
1.0
External events
Reports
Report process
3.0
Business event data
Financial Statements
Internal events
Maintain process
2.0
External events
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Exhibit A-9 Level Zero DFD Example
1.0Process Customer Orders
DesiredInformation
Order
Shipping Request
2.0Deliveries to Customers
Decision Makers
Bill
Customers
Accounts Receivable
Payments
DesiredInformation
3.0Process Payments
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Level One - Record Event Data
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Version 1
Example Data Flow Diagram
Example Flowchart
33
Version 2
Example Data Flow Diagram
Example Flowchart
Errors
Old Earnings Master File
New Earnings Master File
Time Card Data
34
Version 3
Example Data Flow Diagram
Example Flowchart
Factory supervisor
Time cards
Review time cards
Reviewed time cards
Record weekly wages
A alphabetic