DFD examples

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Creating DFDs

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Define Entities • External entities represent

persons, processes or machines which produce data to be used by the system or receive data that is output by the system

• Examples: Student, Customer, Client

Define Processes• Processes are discrete actions

that transform input data to output data

• Examples: Create Student Record, Calculate Purchase Cost, Register Client

Student

2.1

Create Student Record

Creating DFDs (cont’d)Define Data Stores

• Data stores are temporary or permanent repositories of information that are inputs to or outputs of processes

• Examples: Student Master, Client List

Define Data Flows• Data flows represent the

transfer of data over time from one “place” (entity, process, data store) to another

• Examples: New Student Information (from Student, to Student Master)

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New Student Information

Student Master

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Creating DFDs (cont’d)Define the System

• A system is the collection of all business processes which perform tasks or produce outputs we care about. It is “what happens.”

• The system is a single process, connected to external entities

• Represented in a “Context Diagram”

Define Subsystems• A subsystem gives a more

detailed view individual processes contained in the context diagram

• Includes data stores, more elementary processes

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DFDs Created by Top-Down AnalysisCreate a narrative: description of

systemCreate a Context Diagram that

contains a single process (“the system”) and all entities which share data with the system

Explode the “parent” context diagram to produce a Diagram 0 (“child”) DFD

Create Diagram 1, 2, …, n DFDs that represent “explosions” of Diagram 0, 1, …, n-1 DFDs until a diagram has only “primitive” processes

Create process descriptions to be implemented by application programs: queries, macros, reports, programming languages

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Context Diagram

Diagram 0 DFD

Diagram 1 DFDs

Diagram n DFDs

Narrative

E-R Diagram Process Descriptions

Where to Begin Creating DFDsStart with the data flow from an external entity

and work forwards

Start with the data flow to an external entity and work backwards

Examine the data flows into or out of a data store

Examine data flows, entity connections and data stores associated with a particular process

Note fuzzy, ill-defined areas of the system for further clarification

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What to Avoid in DFDs

Making the data flow diagram too cluttered (e.g. 9 processes)

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4

Perform Repair

Processes with no outputs or no inputs

1 2 3Many processes with a single input and output (linear flow)

Processes whose inputs are obviously inadequate to yield

outputs

Having data flows terminate at data stores

Connecting data stores directly to each other

Courses StudentsClass List

Connecting entities to anything other than processes

Payroll Department

Employees

Process A

Process B

Process C

Creating Data Flow Diagrams

Lemonade Stand Example

Creating Data Flow Diagrams

Steps:

1. Create a list of activities

• Old way: no Use-Case Diagram

• New way: use Use-Case Diagram

2. Construct Context Level DFD(identifies sources and sink)

3. Construct Level 0 DFD (identifies manageable sub processes )

4. Construct Level 1- n DFD (identifies actual data flows and data stores )

Example

The operations of a simple lemonade stand will be used to demonstrate the creation of dataflow diagrams.

Creating Data Flow Diagrams

1. Create a list of activitiesExample

Think through the activities that take place at a lemonade stand.

Customer OrderServe ProductCollect PaymentProduce ProductStore Product

Creating Data Flow Diagrams

Example

Also think of the additional activities needed to support the basic activities.

Customer OrderServe ProductCollect PaymentProduce ProductStore ProductOrder Raw MaterialsPay for Raw MaterialsPay for Labor

1. Create a list of activities

Creating Data Flow Diagrams

Example

Group these activities in some logical fashion, possibly functional areas.

Customer OrderServe ProductCollect Payment

Produce ProductStore Product

Order Raw MaterialsPay for Raw Materials

Pay for Labor

1. Create a list of activities

Creating Data Flow Diagrams

0.0Lemonade

SystemEMPLOYEECUSTOMER

PayPayment

Order

Context Level DFD

Example

Create a context level diagram identifying the sources and sinks (users).

Customer OrderServe ProductCollect Payment

Produce ProductStore Product

Order Raw MaterialsPay for Raw Materials

Pay for Labor

VENDOR

PaymentPurchase Order

Production Schedule

Received GoodsTime Worked

Sales Forecast

2. Construct Context Level DFD(identifies sources and sink)

Product Served

Creating Data Flow Diagrams

Level 0 DFD

Example

Create a level 0 diagram identifying the logical subsystems that may exist.

Customer OrderServe ProductCollect Payment

Produce ProductStore Product

Order Raw MaterialsPay for Raw Materials

Pay for Labor

3. Construct Level 0 DFD (identifies manageable sub processes )

2.0Production EMPLOYEEProduction

Schedule

1.0Sale

3.0Procure-

ment

Sales Forecast

Product Ordered

CUSTOMER

Pay

Payment

Customer Order

VENDOR

Payment

Purchase Order Order Decisions

Received Goods

Time Worked

Inventory

Product Served

4.0Payroll

Creating Data Flow Diagrams

Level 1 DFD

Example

Create a level 1 decomposing the processes in level 0 and identifying data stores.

4. Construct Level 1- n DFD (identifies actual data flows and data stores )

1.3Produce

Sales Forecast Sales ForecastPayment

Customer OrderServe ProductCollect Payment

Produce ProductStore Product

Order Raw MaterialsPay for Raw Materials

Pay for Labor

1.1Record Order

Customer Order

ORDER

1.2Receive Payment

PAYMENT

Severed Order

Request for Forecast

CUSTOMER

Creating Data Flow Diagrams

Level 1 DFD

Example

Create a level 1 decomposing the processes in level 0 and identifying data stores.

4. Construct Level 1 (continued)

Customer OrderServe ProductCollect Payment

Produce ProductStore Product

Order Raw MaterialsPay for Raw Materials

Pay for Labor

2.1Serve

Product

Product Order

ORDER

2.2Produce Product

INVENTORTY

Quantity Severed

Production Schedule

RAW MATERIALS

2.3Store

Product

Quantity Produced & Location Stored

Quantity Used

Production Data

Creating Data Flow Diagrams

Level 1 DFD

Example

Create a level 1 decomposing the processes in level 0 and identifying data stores.

4. Construct Level 1 (continued)

Customer OrderServe ProductCollect Payment

Produce ProductStore Product

Order Raw MaterialsPay for Raw Materials

Pay for Labor

3.1Produce Purchase

Order

Order DecisionPURCHASE

ORDER

3.2Receive

Items

Received Goods

RAW MATERIALS

3.3Pay

Vendor

Quantity Received

Quantity On-Hand

RECEIVED ITEMS

VENDOR

Payment Approval

Payment

Creating Data Flow Diagrams

Level 1 DFD

Example

Create a level 1 decomposing the processes in level 0 and identifying data stores.

4. Construct Level 1 (continued)

Time Worked

Customer OrderServe ProductCollect Payment

Produce ProductStore Product

Order Raw MaterialsPay for Raw Materials

Pay for Labor

4.1Record Time

Worked

TIME CARDS

4.2Calculate

Payroll

Payroll Request

EMPLOYEE

4.3Pay

Employee

Employee ID

PAYROLL

PAYMENTS

Payment Approval

Payment

Unpaid time cards

Process Decomposition

4.1Record Time

Worked

4.2Calculate

Payroll

4.3Pay

Employee

3.1Produce Purchase

Order

3.2Receive

Items

3.3Pay

Vendor

2.1Serve

Product

2.2Produce Product

2.3Store

Product

1.1Record Order

1.2Receive Payment

2.0Production

1.0Sale

3.0Procure-

ment

4.0Payroll

0.0Lemonade

System

Level 0 Level 1Context Level

DFD Example: Bus Garage RepairsBuses come to a garage for repairs. A mechanic and helper perform the repair, record the reason for

the repair and record the total cost of all parts used on a Shop Repair Order.

Information on labor, parts and repair outcome is used for billing by the Accounting Department, parts monitoring by the inventory management computer system and a performance review by the supervisor.

Key process (“the system”): performing repairs and storing information related to repairs

External Entities: Bus, Mechanic, Helper, Supervisor, Inventory Management System, Accounting Department, etc.

Processes: Record Bus ID and reason for repair Determine parts needed Perform repair Calculate parts extended and total cost Record labor hours, cost

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DFD Example: Bus Garage Repairs (cont’d)Data stores:

Personnel file Repairs file Bus master list Parts list

Data flows: Repair order Bus record Parts record Employee timecard Invoices

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Bus

Mechanic

Helper0

Bus Repair Process

Supervisor

Accounting

Bus Garage Context Diagram

Mechanical problem to be repaired

Labor

Labor

Fixed mechanical problems

Inventory Management

System

Repair summary

List of parts used

Labor, parts cost details