DATA FLOW DIAGRAMS (DFD):

Sources and Sinks:– Define System Boundaries

Process (transformation)– transforms data - no detail of how the transformation is done– Inputs and Outputs– Manual / Automated– Process #, Brief descriptive label (action verb and object

clause)

Label

(External

Entities)

1.Receive Orders

1Order Clerk:Order Entry

#Desc.Who

Data Store:

– only processes can connect to data stores– A store is passive, process initiates flows

Data Flow:

# InvoicesInvoices

Identifiers (letters,etc)

Name

Customer

Customer

Warehouse

1.Receive Order

2.Ship goods

3.Collect Pmts

Invoices

Orders

Customers

Pmt. Inquiries

Invoice Statement

Cust.Name,Address

Cust.Name,Address

Cust.Name,Address

Shipping DetailGoods info

Goods info

Invoice Details

OrdersInvalid Orders

Billing Info

DFD Example

Order Detail

Data Store:• may be a fundamental user requirement or an

implementation store placed there for convenience.

Enter Order Process Order(Essential Model)

Validated Order

Acknowledgement

Order Detail

Enter Order Process OrderOrders

Acknowledgement

Order Detail

xx yy

(Implementation Model)

Update/Create

Use/Retrieval

Naming data Flows:

Enter orderOrders

Orders? What transformation

For Essential model name should be implementation free

e.g. Course Request Form vs. Form23

Employee

Create newmember account

1.

Freeze accountnumber

2.

Generateemployeebank stat.

3.

AccountsReceivable

Dept

Employee fileMember Accts.

Modified accountstatus

Employeestatus

Employee IDand address

Frozen acct. notification

Existingaccount

Membershipapplication

Bank statement

Common DFD Errors

• Common DFD Errors:

– Process1 has inputs but produces no outputs. This is called a black hole

– Process 2 produces outputs but receives no inputs. This is called a miracle

– Process 3 has inputs and outputs ; however the inputs are not sufficient to produce the outputs. This is called a gray hole.

DS1 DS Name

E-1

2.0P-2

E-2

1.0P-1

DF-2

DF-3

DF-5

DF-4DF-6

DF-2

DF-1

DFD Errors

Pay Phone

Bill

Phone Company

Itemized Calls

Statement and Invoice

Correct Use of Packet Concept

Itemized Calls

Statement

Invoice

The Data Flow Packet Concept

Authorize Payment by Bank

Card

Customer

Credit Vouchers Due

Payments

Credit Receipt

Authorize Payment by Bank

Card

Customer

Credit Vouchers Due

Payments

Customer Receipt

Approved Credit Voucher

Sale

Diverging data flows are implementation oriented and should be avoided on essential DFDs

Diverging Data Flows

The Explosion Approach to drawing DFDs:As suggested by DeMarco and others, this diagramming technique requires the analyst to draw multiple DFDs, each one exploding from a single process on another diagram, until the system is completely modeled

mThe

System

1.2

1.

pn

3.

2.

1.3

1.1.3.1 3.2

ZZZ

XXX

A

H

G

Z

DE

C M

L

KA

B

B

A C

BD

Z

Overview DFD

Context DFD

1.0

1.4 2.3

2.22.1

1.4.1

1.4.41.4.3

1.4.2

1.3

1.1 1.2

3.02.0

Explodes to

Explodes toExplodes to

Level 2 Diagram 1.4

Level 1 Diagram 1

Level 1 Diagram 2

Grandchild

Child Child

ParentFunctional Decomposition and Leveled DFDs

id

TOP - DOWN analysis & functional decomposition

1.function

A

0The System

1.1Activity 1 of function A

Task 1.1.1

Task 1.1.2

Task 1.1.3

1.2Activity 2 of function A

Task 1.2.1

Task 1.2.2

2.1Activity 1 of function B

Task 2.1.1

Task 2.1.2

2.2Activity 2 of function B

Task 2.2.1

Task 2.2.2

Task 2.2.3

2.function

B

Decomposition Diagram

Levelled Set of DFDs• How many levels - not > 9 processes in single DFD• Different parts of system can have different level of detail• Consistency (Balancing) - inflow and outflow to process must

correspond in next level DFD• External entities,data stores,parent processes can, but need not

be repeated in child diagram• Data Stores at different levels - show data store at the highest

level where it first serves as an interface between two or more processes

Top- Down Analysis and Functional Decomposition

Carson-Plymouth Medical Devices (CPMD), as assembler of sophisticated medical products, must maintain a ready supply of high-quality components to manufacture its products. To achieve this goal, CPMD’s purchasing department checks inventory levels each day by reviewing the inventory items stock list. When the quantity-on-hand of a particular item reaches its economic reorder point, CPMD’s purchasing department places a purchase order with its supplier (supplier data is accessed through the supplier file) for that component and files a copy in the purchase order file. When a supplier delivers a shipment along with a bill of lading, shipping and receiving (S/R) receives the shipment by performing a three-step process. First, the S/R clerk verifies the shipment by accessing a copy of the purchase order and comparing it to the bill of lading. If a received item appears on the purchase order and the bill of lading, the verified bill of lading and received items are passed on to Inspection. Otherwise, the S/R clerk generates a notice of shipment error, which is sent to the supplier.Next, the inspector inspects the valid shipment items by accessing the quality criteria, from the inspection criteria folder. If the item meets all the quality criteria, the inspector adds it to an accepted items list, which is forwarded to the inventory clerk. If an item does not pass inspection, the inspector creates a notice of defective shipment, which is sent to the supplier along with the defective items. Finally, the inventory clerk updates the inventory items list by adding the current-on-hand quantity, reflecting an updated quantity.

Carson-Plymouth Medical Devices (CPMD), as assembler of sophisticated medical products, must maintain a ready supply of high-quality components to manufacture its products. To achieve this goal, CPMD’s purchasing department checks inventory levels each day by reviewing the INVENTORY ITEMS STOCK list. When the quantity-on-hand of a particular item reaches its economic reorder point, CPMD’s purchasing department places a purchase order with its supplier (supplier data is accessed through the SUPPLIER file) for that component and files a copy in the PURCHASE ORDER file. When a supplier delivers a shipment along with a bill of lading, shipping and receiving (S/R) receives the shipment by performing a three-step process. First, the S/R clerk verifies the shipment by accessing a copy of the purchase order and comparing it to the bill of lading. If a received item appears on the purchase order and the bill of lading, the verified bill of lading and received items are passed on to Inspection. Otherwise, the S/R clerk generates a notice of shipment error, which is sent to the supplier.

Next, the inspector inspects the valid shipment items by accessing the quality criteria, from the INSPECTION CRITERIA folder. If the item meets all the quality criteria, the inspector adds it to an accepted items list, which is forwarded to the inventory clerk. If an item does not pass inspection, the inspector creates a notice of defective shipment, which is sent to the supplier along with the defective items. Finally, the inventory clerk updates the INVENTORY ITEMS list by adding the current-on-hand quantity, reflecting an updated quantity.

Carson-Plymouth Medical Devices (CPMD), as assembler of sophisticated medical products, must maintain a ready supply of high-quality components to manufacture its products. To achieve this goal, CPMD’s purchasing department checks inventory levels each day by reviewing the INVENTORY ITEMS stock list.

Process Ext. Entity Input Output Data Store

check inventory inventory levels from items to reorder inventory levels Inventory list items

When the quantity-on-hand of a particular item reaches its economic reorder point, CPMD’s purchasing department places a purchase order with its supplier (supplier data is accessed through the SUPPLIER file) for that component and files a copy in the PURCHASE ORDER file.

Process Ext. Entity Input Output Data Store

create a PO supplier items to reorder, PO to supplier, inv items supplier data PO to file supplier, from Supplier file PO

When a supplier delivers a shipment along with a bill of lading, shipping and receiving (S/R) receives the shipment by performing a three-step process. First, the S/R clerk verifies the shipment by accessing a copy of the purchase order and comparing it to the bill of lading. If a received item appears on the purchase order and the bill of lading, the verified bill of lading and received items are passed on to Inspection. Otherwise, the S/R clerk generates a notice of shipment error, which is sent to the supplier.

Process Ext. Entity Input Output Data Storeverify Supplier bill of lading; verified bill PO

copy of PO of lading, notice of shipment errors to Supplier

Next, the inspector inspects the valid shipment items by accessing the quality criteria, from the INSPECTION CRITERIA folder. If the item meets all the quality criteria, the inspector adds it to an accepted items list, which is forwarded to the inventory clerk. If an item does not pass inspection, the inspector creates a notice of defective shipment, which is sent to the supplier along with the defective items. Process Ext. Entity Input Output Data StoreInspect Supplier verified bill of lading; accepted items Inspection Shipment inspection criteria list; defective Criteria

from Inspection shipment notice Criteria Folder to Supplier

Finally, the inventory clerk updates the INVENTORY ITEMS list by adding the current-on-hand quantity, reflecting an updated quantity

Process Ext. Entity Input Output Data Store

Update Accepted items updated inv levels Inv. ItemsInventory list, current inv.

levels

Verify shipment

Check inv levels

Create PO

Inspect shipment

Update Inv.

Supplier

DS1 Supplier

DS2 PO File

DS2 Inspection Criteria

DS4 Inventory Item

Notice of defective shipment

Bill of lading

P.O.

Items to reorder

Low items

Current Data

Updated data

Supplier data

New PO data

PO info

Accepted items list

Verified bill of lading

Notice of shipment error

Inspection Criteria1.

2.

3.

4.

5.

Level 0 DFD

4.1

Identify Inspection Criteria

4.2

Inspect Items

4.3

Prepare notice of defective shipment

DS1 SupplierInspection criteria

Item numbers, criteria

Defective items data

Accepted items list

Notice of defective shipment

Level-1 DFD for Inspect Shipment

Context and level 0 DFD

When parts are received from vendors, they are accompanied by an invoice. Mrs Gauron in the Receiving Dept checks the invoice against the orders file to be certain that the correct parts were delivered. If the parts were not ordered or the order was incorrectly filled, parts are returned. If the parts are correct, the inventory file is updated to reflect the new quantity of these parts. This is done by increasing the data element quantity-on-hand by the quantity-record for the part-id . Mrs Gauron then prepares the payment for the vendor. She also enters the payment transaction in the general ledger, which is maintained as the bound accounting ledger. A worker on the factory floor who needs a part requests it by submitting a requisition to the parts clerk. The information on this form is used to update the inventory file. Each week the parts clerk uses the inventory file to prepare a report listing all parts whose quantity- on- hand has fallen below the reorder point. For parts listed on the report, a purchase request form is prepared and sent to the purchasing office.

[ Hint: do not confuse the processes being performed with the people who perform them ]

Vendor

Floor

Purchasing Office

0.Inventory

System

Context level DFD

Invoice

Projected Part

Payment

Requisition

Purchase Request Form

Order File

Inventory

General Ledger5.

Check part for reorder

4.Provide

part

2.Update Part Qty

3.Pay

Vendor

1.Check invoice

6.Prepare

purchase request Floor

Purchasing office

Vendor

Invoice

Rejected Part

Payment

Payment Info

Order record

ApprovedInvoice

ApprovedInvoice

Part-id,Qty

Inv. record

Used Part info

RequisitionReorderInfo

Purchase request form

Delta Products Corporation is a major vendor of office supplies, furniture and equipment. Delta’s sales representatives call on customers to take orders. The sales rep write up the orders and turn them in to a sales order processing (SOP) clerk at the regional center. If the order items are in stock, the SOP clerk prepares a picking slip and packing list for each order. If any of the ordered items are out of stock, the SOP clerk completes an out of stock Notice forms, which notes the number of customer requiring the items and forwards it to Purchasing. A Purchasing clerk then completes a purchase order,which is mailed to a supplier. The SOP clerk notes back-ordered items on the customer’s order and forwards a copy of annotated customer order to Accounts receivable, where a A/R clerk prepares an invoice and sends it to the customer. The SOP clerk also forwards a picking slip and packing list to the warehouse, where stock price pickers fill the order,placing ordered items into boxes alongwith the packing list. The boxed items and packing list are held for delivery, usually via UPS.

• Context Diagram• Level 0 DFD• Level 1 DFD for functions related to the sales-order processing clerk

CustomerCustomerEE-1

SupplierSupplierEE-2

ProcessOrder

2.*

WriteOrder

1

Order Information

Written Order

BillCustomer

4

Invoice

Annotated Order

PurchaseInventory

5

Out of Stock Notice

PurchaseOrder

FillOrder

3

UPSUPSEE-3

Packing List&

Picking Slip

D-1 Inventory Items

UpdatedInventory

CurrentInventory

Level 0 DFD for Delta Products’ Order Fulfillment System

CheckItem

Availability

2.1

D-1 Inventory ItemsUpdated Inventory

Current InventoryWritten Order

PrepareOoS

Notice

2.3

AnnotateOrder

(backordered items)

2.2

PurchaseInventory

5

BillCustomer

4

Preparepacking list

& picking slip

2.4

FillOrder

3

Packing List & Picking Slip

Annotated Order

Out of Stock NoticeOut of Stock items order

In-Stock items order

Level 1 Process 2.0 - Process Order