Mastering Process Modeling: A Visual Guide to Data Flow Diagrams

Objectives:
• Understand and follow rules and guidelines for DFDs.
• Learn the step-by-step process to create DFDs.
• Apply concepts by creating various levels of DFDs.

Process Modeling?
• It’s a visual (graphical) way to show how a business system works.
• It helps to understand what activities are done and how data moves
between them.
• It can be used to represent the current system (as-is) or the future
system (to-be).

• External Entities / Source & Sink
• Process
• Data Flow
• Data Store
Components of DFDs

External Entity:
LCA (Lawn Chemical Applicator) is the main user.
He/she starts the process by asking for a chemical.

Main Steps (Processes 2.1 to 2.5):
2.1 Determine Chemical Approval Status
• Checks if the chemical is approved or not.
• It looks into a storage file called Lawn Chemicals Supply.
• If not approved, it sends back a rejection.
• If approved, it moves to the next step.
2.2 Determine Request Quantity
• Tells the LCA how much chemical is available.
• LCA then says how much they want.
• If the request is okay (not too much), the system accepts it.

2.3 Confirm Request
• Confirms the request made by LCA.
• Saves the request in a storage called Chemical Requests.
• Tells LCA that the request is confirmed.
2.4 Update Available Chemical Quantity
• Reserves the amount of chemical requested so others can't take it.
• Updates the storage to reflect the new available quantity.
• If there’s not enough, it informs Purchasing about a chemical shortage.

2.5 Prepare Pick-up Material
• Prepares the pick-up info.
• Notifies the Chemical Supply Warehouse to get the chemical ready.
• Sends pick-up authorization to the LCA.

Data Stores:
• D1: Lawn Chemicals Supply – where info about chemical stock and
approval is kept.
• D2: Chemical Requests – where confirmed requests are saved.

1. Process
• A business function or activity that transforms inputs into outputs.
• Starts with a verb + ends with a noun (e.g., Determine Quantity).
• Requirements:
• Has a number, name, and description
• Must have at least one input and one output data flow
• Symbols:
• Gane & Sarson: Rounded rectangle with label and number
• DeMarco/Yourdon: Oval

2. Data Flow
• Represents movement of data between processes, data stores, and
external entities.
• Noun (e.g., Customer Info)
• Requirements:
• Must connect to a process
• Can flow to or from data stores or external entities
• Symbol: Arrow with label (→)

3. Data Store
• A collection of data that is stored for later use.
• Noun (e.g., Inventory)
• Requirements:
• Has a number, name, and description
• Has input and/or output data flows
• Symbols:
• Gane & Sarson: Open-ended rectangle
• DeMarco/Yourdon: Two parallel lines

4. External Entity
• A person, organization, or system outside the scope of the system
that interacts with it.
• Noun (e.g., Customer, Bank)
• Requirements: Has a name and description
• Symbol: Square/Rectangle

1. Context diagram
A context diagram is the top-level (highest level) view of a system. It
shows:
• The entire system as a single process
• The external entities (people, other systems) that interact with the
system
• The data flows going into and out of the system

Step 1 : Identify Process - name of the system.
Step 2 : Identify External Entities – stakeholders, and draw it around the perimeter
of the page.
Step 3 : Identify Data Flows
** Remember the Rules:
• Follow naming conventions.
• Do not represent detail data flows as from entity to entity.
Context Diagram

• Guidelines for Drawing DFDs
• Draw the context diagram so that it fits on one page
• Use the name of the information system as the process name in the context diagram
• Use unique names within each set of symbols
• Do not cross lines
• Provide a unique name and reference number for each process
• Ensure that the model is accurate, easy to understand, and meets the needs of its
users
Creating a Set of DFDs

Creating a Set of DFDs
2
FIGURE 5-13 Context diagram
DFD for an order system
• Step 1: Draw a Context
Diagram

Basic Data Flow Diagramming Rules

Common Mistakes in DFD
Slide 21 (of 21)

2. Level 0 DFD?
• A Level 0 Data Flow Diagram (DFD) is the next step after the context
diagram. It:
• Breaks down the single process (process 0) from the context diagram
into major sub-processes (e.g., 1, 2, 3).
• Shows data stores (where information is stored within the system).
• Includes external entities and data flows, just like the context
diagram.
• Provides more internal detail of how the system works.

• Also called child diagram
• Is exploded from parent diagram
• When drawn, should be
• leveled
• also called exploded, partitioned and decomposed
• drawn in a series of increasingly detailed diagrams until desired degree of
detail is reached
• balanced
• maintain consistency among the entire series of diagrams
Also called Lower-level diagrams

Step 1 : Identify related process – main functionalities/ sub-modules
Step 2 : Identify Data Flows to/from External Entities to/from identified processes,
at the same time identify Data Store needed
Step(s) to Draw
Data Flow Diagram Level 0

2. Level 0 DFD?
• Balancing means the inputs and outputs of a higher-level diagram (like the
context diagram) should match the flows in the next level (like the Level 0 DFD).
In this figure:
• Inputs and outputs to/from external entities (X, Y, Z) in the context diagram also
appear in the Level 0 DFD.
• The internal structure of process 0 is shown using processes 1, 2, and 3.
• New internal flows (A and B) are added to show how these sub-processes
connect.
• D1 is introduced because now we are zooming into the system’s internal
storage.

Creating Level 0 DFD
3
FIGURE 5-16 Diagram 0 DFD for the order system
• Step 2: Draw a Diagram 0 DFD
• If same data flows in both
directions, you can use a double-
headed arrow
• Diagram 0 is an exploded view of
process 0
• Parent diagram
• Child diagram

• A second class of DFD mistakes arise when the outputs from one processing step
do not match its inputs.
• It is not A processing step may have input flows but no output flows. This situation is
sometimes called a black hole.
• A processing step may have output flows but no input flows. This situation is
sometimes called a miracle.
• A processing step may have outputs that are greater than the sum of its inputs - e.g.,
its inputs could not produce the output shown. This situation is sometimes referred
to as a grey hole.
• hard to list situations in which this might occur:
Diagramming Mistakes in DFD

Let’s find the mistakes!
1. Process 1.0 (P2) has only inputs, making it a “black hole”.
2. Data flow DF5 should not move directly from source E1 to data store DS1 without first going through a
process.
3. Data flow DF1 should not move directly from source E1 to sink E2 without first going through a process.

3. Level 1 DFD
• A Level 1 Data Flow Diagram (DFD) is a more detailed breakdown of
one of the processes from the Level 0 DFD.
• Each major process from the Level 0 DFD is decomposed into sub-
processes.
• These sub-processes are numbered based on their parent.
(For example: process 2 from the Level 0 DFD becomes 2.1, 2.2, 2.3 in
the Level 1 DFD.)
• It shows how data moves between these sub-processes and data
stores, but does not always show where data originates or goes
outside the process — for that, we refer to the Level 0 DFD.

3. Level 1 DFD
• Balancing means that the inputs and outputs of Process 2 in the Level
0 diagram match what we see in this Level 1 diagram.
• Level 0 shows:
• Inputs: B, M
• Outputs: A, N, Y
• Interaction with Data Store D1

FIGURE 5-17 Diagram 1 DFD shows
details of the FILLORDER process in
the order system
• Step 3: Draw the Lower
Level Diagrams
• Must use leveling and
balancing techniques
• Leveling examples
• Uses a series of
increasingly detailed
DFDs to describe an
information
system
• Exploding, partitioning,
or decomposing

4
FIGURE 5-19 The order system diagram 0 is shown at the top of the figure, and exploded diagram 3 DFD (for the
APPLY PAYMENT process) is shown at the bottom. The two DFDs are balanced because the child diagram at the
bottom has the same input and output flows as the parent process 3 shown at the top

4
FIGURE 5-21 In the next level of
detail, the process 0 black box reveals
three processes, two data stores, and
four internal data flows — all of which
are shown inside the dashed line
FIGURE 5-20 Example of a parent
DFD diagram, showing process 0 as a
black box

Process Decomposition
4.1
Record
Time
Worked
4.2
Calculat
e
Payroll
4.3
Pay
Employ
ee
3.1
Produce
Purchas
e Order
3.2
Receive
Items
3.3
Pay
Vendor
2.1
Serve
Product
2.2
Produce
Product
2.3
Store
Product
1.1
Record
Order
1.2
Receive
Paymen
t
2.0
Producti
on
1.0
Sale
3.0
Procure-
ment
4.0
Payroll
0.0
Lemonad
e System
Level 0 Level 1
Context Level

4. Level 2 DFD
• A Level 2 Data Flow Diagram is a further breakdown of a single
process from a Level 1 DFD.
• It gives even more detail about what happens inside a specific
process.
• Each process in this level is numbered with two decimal points, e.g.,
2.2.1, 2.2.2, 2.2.3, meaning these are parts of Process 2.2.

4. Level 2 DFD
• This Level 2 diagram is balanced with the Level 1 DFD for Process 2.2
because:
• It has the same inputs (H, K) and outputs (C, G).
• It still interacts with Data Store D1 (N).
• The internal workings are just shown in more detail — nothing is
added or missing in terms of what goes in or comes out of Process
2.2.

Interview: Sarah (systems analyst) and Hal
(owner, Holiday Travel Vehicles)
• The interview with Hal (business owner) provides a clear picture of
how Holiday Travel Vehicles operates.
• Here's a concise breakdown of the business processes, requests,
and system requirements based on the discussion with Sarah, the
systems analyst:
BUSINESS SUMMARY
Core Business:
Selling new and used recreational vehicles (RVs) and trailers, with
seasonal inventory management and customer customization.

MAJOR BUSINESS PROCESSES
1. Vehicle Ordering and Inventory
• Order Placement: Vehicles are ordered from 5 main suppliers.
• Vehicle Arrival & Recording:
• When new vehicles arrive, details like VIN, model, year, cost, etc., are
recorded using a New Vehicle Form and stored physically in a file cabinet.

2. Sales Process
a. Customer Interaction
• Customers browse without data
collection until they decide on a vehicle.
• An Offer Form is filled once the customer
chooses a vehicle.
b. Offer Evaluation
• Offer includes:
• Customer name
• Vehicle chosen
• Offered price
• Trade-in vehicle details (if any)
Trade-in value is determined by a
Used Vehicle Manager.
Owner (Hal) reviews the offer
using:
• New Vehicle Form (for vehicle
cost)
• Green Book (for trade-in value)
• If changes are needed, a new
Offer Form is written; old ones are
destroyed or stored for follow-up.

3. Sales Finalization
• Upon Offer Acceptance:
• A Sales Contract is filled out with:
• Full customer details
• Vehicle + trade-in info
• Dealer-installed options
• Final price, taxes, deposit
• Salesperson info (for commission)
Financing:
• Customer arranges their own financing;
HTV refers them to local banks.
Records:
• Vehicle Purchase Record is created and
combined with the New Vehicle Form.
• Stored by customer name for future
reference.
Shop Work Order: Issued for
prep/installation of dealer options.

4. Vehicle Delivery
• Customer brings payment and trade-in vehicle.
• Final walkthrough and signature.
• Receives vehicle keys + a copy of Sales Contract.
• Records (Sales Contract + Purchase Record) are finalized.

5. Trade-In Processing
• A Used Vehicle Form is completed with trade-in info.
• If needed, a shop work order is created to prep the used vehicle for
resale.
6. Bookkeeping
• After final delivery, sales data (price, taxes, fees) are recorded in a
Sales Ledger for bookkeeping.

BUSINESS REQUEST
Hal and HTV are seeking:
• A new information system to improve efficiency, accuracy, and
record-keeping.
• Better handling of vehicle inventory, customer offers, trade-ins, and
finalized sales.
• Eliminate manual/paper forms and physical filing.
• Facilitate communication among staff (salespeople, owner, used
vehicle manager, shop, and bookkeeper).

SYSTEM REQUIREMENTS (Functional
Requirements)
1. Inventory Management:
• Record and track new vehicle data on arrival.
• Manage trade-in vehicle details and condition.
2. Sales Support:
• Create and manage offer forms digitally.
• Retrieve vehicle and trade-in details during negotiations.
• Store and access customer-specific offers.
3. Offer Evaluation:
• Support owner decision-making with easy access to vehicle cost and trade-in values.
• Track rejected, pending, and accepted offers.

Requirements)
4. Sales Contract & Delivery:
• Generate formal contracts.
• Capture all sale-related info: vehicle, customer, pricing, options.
• Track delivery status and customer confirmation.
5. Shop Integration:
• Automatically generate work orders for dealer-installed options or
trade-in prep.
6. Bookkeeping Integration:
• Record sales data, taxes, and fees in a sales ledger system.

Requirements)
7. Reporting & Follow-Up:
• Generate reports for sales, inventory, and customer activity.
• Track follow-up actions for rejected offers.

SYSTEM REQUIREMENTS (Non- Functional
Requirements)
• User-friendly interface for non-technical staff.
• Secure access controls (e.g., only managers can accept/reject offers).
• Data integrity and backup for legal and financial safety.
• Integration capability with external systems (e.g., banks, accounting
tools).

Creating Data Flow Diagram Fragments

• A Level 0 DFD (also called a context-level diagram) gives a high-level
overview of a system’s main processes, data flows, data stores, and
external entities.
• It's one level deeper than the context diagram, showing the major
sub-processes but still abstracting away detailed logic.

• A Level 1 DFD takes each major process from the Level 0 DFD and
breaks it down into smaller steps.
• Each step in a use case becomes its own process on the Level 1 DFD.
• Inputs and outputs of those steps become data flows.
• External entities (e.g., Customer, Salesperson) and data stores (e.g.,
Pending Offers, Payments) are often included to make the diagram
easier to understand.

To understand and apply Data Flow Diagrams (DFDs), use case modeling,
and scenario writing for a real-world system. You will analyze, model, and
document a system using Context Diagram, Level 0, Level 1, and Level 2
DFDs, along with use case diagrams and scenarios.
Choose One System to Model:
1. Garage Management System
2. Currency Exchange System

Part 1: System Analysis
Task 1.1: Describe the System
• Write a brief overview of your chosen system.
• Identify the main goals (e.g., managing vehicle services, currency
transactions).
Task 1.2: Identify System Actors
• List all users or systems that interact with your system (e.g., customer,
mechanic, cashier, teller).
• Briefly describe their roles.

Part 2: Use Case Modeling
Task 2.2: Write Use Case Descriptions
• Choose 3 use cases and write a detailed description for each:
• Use Case Name
• Actor(s)
• Preconditions
• Main Flow (step-by-step)
• Alternate Flows (if any)
• Postconditions

Part 3: Data Flow Diagram Development
Task 3.1: Create a Context Diagram
• Show your entire system as one process.
• Include all external entities and the major data flows.
Task 3.2: Create a Level 0 DFD
• Break the system into 4–6 main processes.
• Connect processes to data stores and external entities.
• Label all data flows clearly.
Task 3.3: Create a Level 1 DFD
• Choose one process from Level 0.
• Break it into sub-processes.
• Include all relevant data stores and flows.
Task 3.4 (Optional for bonus): Create a Level 2 DFD
• Pick a sub-process from Level 1 and break it down further.
• Ideal for complex parts like "Manage Service" or "Process Transaction".

Part 4: Data Modeling
Task 4.1: Identify Data Stores
• List all data stores (e.g., Customer Info, Vehicle Records, Transactions).
• Describe the type of data in each.
Task 4.2: Describe Data Flows
• Write 5 examples of data flows.
• What data is moving?
• From where to where?
• Why is it needed?

Assignment (Garage Management System)
Use Cases:
a. Book Service Appointment
b. Receive Vehicle
c. Assign Mechanic
d. Perform Service
e. Generate Bill
f. Process Payment
Entities:
• Customer
• Receptionist
• Mechanic
• Cashier
• Manager

Assignment (Currency Exchange System)
Use Cases:
a. Register Customer
b. Currency Rate Lookup
c. Initiate Exchange Transaction
d. Confirm Transaction
e. Generate Receipt
Entities:
• Customer
• Teller
• System Admin

Mastering Process Modeling: A Visual Guide to Data Flow Diagrams

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