1. Data Flow Diagrams class
file: dataflows.ppt

2. Managerial mapping tools
Budgets, financial reports
Architectural and geographical blueprints and maps
Flowcharts
Timelines, Gantt and Pert charts
Mission statements
Organizational charts

3. Understanding & documenting processes
Entity-relationship models
Show logical structure of data needed to support business process
Data flow diagrams
Show what is done
Flowcharts
Show how it is done

4. Information System Analysis & Design
2 keys to Information System Development:
* Entity-Relationship Model - analysis and
design of information structure in a system.
* Data Flow Diagram - analysis and design
of the information flow (actually more of the
business processes) in a system.
Concept behind this traditional approach:
Procedure + Data Structure = Program

5. E-R Diagrams

6. Data Flow Diagrams (DFDs)
DFDs are graphic representations of systems
DFDs map how data flows through interconnected processes
Although the name implies data, the emphasis is on processes

7. DFD symbols DFDs consist of only four symbols:
Environmental (external) elements
Processes
Data Flows
Data Storage

8. DFD symbols Environmental (external) elements Processes Data Flows
Data Storage
Supplier
Accounting dept.
Print invoice
Compute net pay
invoice
General ledger

9. Traditional Approach in DFD
Hierarchical Decomposition of Functions - decomposing function process into smaller ones which together accomplish the function.
Top Down Design
Bottom Up Implementation

10. DFD Examples

11. Environmental elements
External elements are those that exist outside the boundaries of the system.
They can be persons, organizations, or other systems.
In a way, they serve to define the system’s boundary.

12. Data Flows
Data flows are any collection of logically related data elements that travel from one process to another. They can be of any size.
Think of a record, a note, a phone call, a letter, or a file.
Data flows can converge or diverge, they can be one or two way flows.

13. Processes Processes are transformations of inputs into outputs.
It is best to label each process as verb, or verb + object.

14. Data Storage
Data stores hold data (while flows are about data-in-motion).

15. Leveled Data Flow Diagrams
Context level diagram
Level 0 diagram (“top level”)
Level n figures (diagrams)
pyramid, granularity.
How deep?
Structured English, pseudocode, flowcharts?

16. Steps to develop DFD (1) Conceptualize data flows from top down–
1. Make a list of business activities and use it to
determine various:external entities, data flows, processes, data stores.
2. Create a Context Diagram: with external
entities and data flows to and from the system
- which is the only process, labeled as #0.
The Context DFD should not have any data
stores, nor any detailed processes.
3. Draw the next level DFD - Diagram 0.

17. Steps to develop DFD (2) 3. Draw the next level DFD ΠDiagram 0. It
should show major business processes and
possible data stores at this level.
4. Create a Child Diagram for each process in
Diagram 0, exploding if necessary.
5. Check for errors and designate good names.
6. Use the DFD to reason about improving the
operation by re-organizing business processes.

18. Context level diagrams
Use only a single process model
Process represents entire system
No numbers
All external entities
Show all in- and outflows of info

19. “Figure “n” diagrams
Each level “explodes” one process on preceeding level
Each level numbered for process it explodes
Include up to seven processes on single diagram
Stopping rule?

20. Exploding…

21. Diagramming guidelines
Label each data flow: use unique names
Keep data flow names constant across levels
Avoid (diagnose) read-only processes
Write-only processes are only allowed under one condition...

22. Creating Diagram 0 1. Start with input from an external entity:
What happens to this data entering the system?
Is it stored?
Is it input for several processes?
2. Work backwards from output data flow:
Where does this data come from?
Is it calculated on demand, or was it stored in a file?
3. Examine data flow to and from a data store:
Which processes put data into the store?
Which processes use the data?
Which processes are responsible for update?

23. Whither and Why DFDs? (Most?) Natural way to document a system
Simple, common communication
Simple, common language
Supported by- and support the creation of CASE

24. Accounts Payable Problem
Consider the following scenario.
Each month you receive bills from various vendors (e.g., phone, auto insurance, credit cards, utilities) and periodically other billings (e.g., magazine subscriptions, university tuition and fees). Consider all of these billings as being examples of invoices from vendors. Like most people you don't pay your bills on the same day that they are received but rather review each invoice and prioritize them in terms of which you will pay first. These reviewed and prioritized invoices are then placed in an old shoe box until you decide you had better start paying some of them.
You remove an invoice from the shoe box and prepare a check to be mailed to the vendor. You check the old balance in your check register and update the register with the check information and compute a new balance. You may do this several times a month.
At the end of the month you receive a statement from your bank that lists the checks that have cleared your account. You (should) take your check register and compare your list of checks and their amounts with the statement that you received from the bank. If everything is in balance then you place an appropriate mark in your check book else you enter a correcting entry (the bank never makes a mistake).

25. Accounts Payable (AP) DFD
Invoice
Vendor
1.0
Approve &
Prioritize
Bills
Vendor
Prioritized
Bills
Check
Invoice
Check
2.0
Prepare
Check
Selected Bill AP
Shoe Box
Check Info
and New
Balance
Statement
Bank
Old Balance
Check Register
Context
Diagram
Balanced Checkbook
3.0
Compare
Register
Info
Bank
Statement

26. Order Entry Problem
SAM's is a mail order catalogue store. A customer fills out the sales order form that is enclosed in the catalogue and mails it to their headquarters in the Bahamas (postage prepaid). Upon receipt, a clerk opens the envelopes and removes the sales order forms. The clerk gives the forms to a data entry operator, who keys the data onto a diskette using a microcomputer. After data entry, the sales orders are filed in a Sales Order History file. The diskette containing all of the sales order data is then read by a minicomputer. For each ordered item, the Inventory Master Record is retrieved from the Inventory master files and the balance on-hand is reduced by the ordered amount. The updated Inventory Master Record is written back to the file. The same program prints picking tickets and writes a Daily Sales Report file onto the system disk. The picking tickets are input to the order filling system where they are used by warehouse personnel in picking the merchandise from the shelves for shipment to the customers. Another minicomputer program reads the Daily Sales Report file and prepares a daily sales report that goes to the sales manager.

27. Sales Order (SO) DFD Process Sales Order Context Diagram Sales Order
1.0
Open Mail
Customer
Customer
Sales
Order
Sales Order Form
2.0
Enter Order
Entered
Sales Orders
Sales Order
History File
Process
Sales
Order
Entered
Sales
Inventory Master Records
to be updated
3.0
Update
Inventory
Master File
Daily
Sales
Report
Inventory
Master File
Picking
Tickets
Updated
Inventory Master Records
Order
Filling
Station
Daily
Sales
Sales
Manager
Order
Filling
Station
Picking
Tickets
4.0
Print Daily
Sales Report
Context Diagram
Sales
Manager
Daily Sales Report

28. Prepare Check Flowchart for AP 2.0
Start
Remove next bill
Get balance
Balance
GT Bill ? No
Yes
Write Check
Return
bill to box
Update Register
```
Yes
More
Bills? No
Stop

29. Open Mail Flowchart for SO 1.0
Start
Start
Open Mail
Open Mail
Remove Sales Order
Remove Sales Order
Place in Pile
Take
S.O. to
Operator
```
Yes
More
Mail?
```
Yes
More
Mail?
Take
pile to
Operator No
Stop
Stop