dfd common mistake

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TOP SEVEN DFD COMMON MISTAKES

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Page 1: DFD Common Mistake

TOP SEVEN DFD

COMMON MISTAKES

Page 2: DFD Common Mistake

Mistake 1 : Verb vs. Noun

.1.0

Order

Verify order

.1.0

Login

Login

Incorrectly labeling processes or data flow

Process labels should be verb phrases

Data flow labels should be noun phrases

CUSTOMER

CUSTOMER

Page 3: DFD Common Mistake

Mistake 2 : DFD Flowchart

DFDs are not Flowcharts

Page 4: DFD Common Mistake

Mistake 3 : 1 2 3 …

• Process are numbered within the diagram NOT according to the correct process flow but for understanding purpose ONLY.

• logical representations - modeling WHAT a system does, rather than physical models showing HOW it does the work

1.0

Fill Order

2.0

CreateInvoice

3.0

ApplyPayment

SALESREP

BANK ACCOUNTING

CUSTOMER WAREHOUSE

Order

Order RejectNotice

Picking List

AccountsReceivableD1

Invoice

Invoice

Invoice DetailPayment

Detail

Payment

Commission Bank Deposit Cash Receipts Entry

Completed Order

Page 5: DFD Common Mistake

Mistake 4 : Complicated• Including more than nine processes on a DFD

– Decomposition is needed• The purpose of data flow diagrams is to provide a semantic bridge between

USERS and systems developers.– User understanding and reviewing

Page 6: DFD Common Mistake

Mistake 5: CD DFD

WAREHOUSECUSTOMER

0

Order System

Order

Payment

In-StockRequest

StatusMessage

Invoice Shipping Confirmation

Shipping Order

Inventory ReportsContext Diagram of Order System

Entity ?Data flow ?

2

8

Page 7: DFD Common Mistake

Mistake 5: CD DFD (cont)

1.0

CheckStatus

2.0

IssueStatus

Messages

ACCOUNTING

CUSTOMER WAREHOUSE

4.0

Manage Accounts

Receivable5.0

ProduceReports

Order In-Stock Request

Status Data

Status Message

PendingOrdersD1

Order Data

Invoice

Payment

Accounts ReceivableD2

Accounting Data Accounts Receivable Data

Order Data

Inventory Reports

DFD Level 0 of Order System

Entity ? 3

Data flow ? 6

3.0

Generate

OrderShipping

Data flow:- Shipping order- Shipping confirmation

Page 8: DFD Common Mistake

Mistake 6: Diagramming rules

Miracles

Black holes

Page 9: DFD Common Mistake

Mistake 7: DFD System

• DFD should reflect/represent the system;)

Page 10: DFD Common Mistake

Tests for Correctness

• Are there any missing data flows?• Are there any extraneous data flows?• Are there any meaningless labels on data flows?• Are there any missing processes?• Are there any errors in leveling?• Are there any deceptive process labels?• Is there any flow of control information?• Is the DFD an accurate representation of reality?

Page 11: DFD Common Mistake

Tips and Guidelines

1. System boundary establishment is an important judgment call. External entities aid in determining where the boundary is established. An interfacing system can be shown as an external entity. It may be necessary to dictate the input of the external entity to assure system control.

2. Label your processes carefully and vividly. A process that is labeled "Produce Report" and has the output of "Report" tells a reviewer very little. If you have trouble labeling anything on the diagram, it often is because you do not have adequate understanding. Choose names carefully.

3. Think logical, not physical. Ignore media, color, font, layout, packaging, time, sequencing, etc. Think "what", not "how". Something logical can be implemented physically in more than one way. Including "when" and "where“ and "how" means you are getting physical.

Page 12: DFD Common Mistake

Tips and Guidelines (cont)

4. Think data, not control flow. Data flows are pathways for data. Think about what data is needed to perform a process or update a data store. A data flow diagram is not a flowchart and should not have loops or transfer of control. Think about the data flows, data processes, and data storage that are needed to move a data structure through a system.

5. Concentrate first on what happens to a "good" transaction. Systems people have a tendency to lose sight of the forest because they are so busy concentrating on the branches of the trees.

6. Reviewers will not be convinced by confusion. A quality data flow diagram will be so simple and straightforward that people will wonder what took you so long.

Page 13: DFD Common Mistake

Tips and Guidelines (cont)

7. Data store to data store, external entity to external entity, or external entity to data store connection usually do not make sense. Data flows with an arrowhead on each end cause confusion in labeling. Do not use them.

8. Do not try to put everything you know on the data flow diagram. The diagram should serve as index and outline. The index/outline will be "fleshed out" in the data dictionary, data structure diagrams, and procedure specification techniques.

Page 14: DFD Common Mistake

The end…Thank you!

Ainee – SAD Team (2007)