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Data Flow Diagramming.

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Presentation on theme: "Data Flow Diagramming."— Presentation transcript:

1 Data Flow Diagramming

2 Data Flow Diagramming Represent processes
…that capture, manipulate, store, & distribute data …between a system & its environment … & among system components.

3 Data Flow Diagramming a process modeling technique Source input
retrieval Data Store # # Process storage output Sink 2.0 Connector Show that data flow continues to another process

4 Context Diagram An overview Represents the System Scope Customers
Sales orders Accepted sales order file Rejected sales order report Order Entry System Inventory System Sales Manager

5 Level-0 Diagram Customers Sales orders Item numbers Item prices
Master item number list 1.0 Screen sales orders Item prices Master price list Accepted sales order file Rejected sales order file 2.0 Sort rejected sales order file Sorted rejected sales order file Inventory System 3.0 Prepare rejected sales order report Rejected sales order report Sales Manager

6 Level 1 Diagram (for Process 1.0) aka: Diagram 1.0
Customers Sales orders 1.1 Verify item number Master item number list Master item number list Item numbers Verified item numbers Accepted sales order file 1.2 Verify price Inventory System Item prices Master price list Master price list Rejected sales order file 2.0

7 DFD Rules Naming Conventions Rules By Type DFDs should: Processes
Accurately represents the system Be Balanced Be Consistent Be Readable Naming Conventions Processes Verb phrase = verb + object e.g. ValidateAccount, CalculateTax Data Flows Noun/noun phrase = adj + object e.g. payment, verified payment Data Stores e.g. Employee, HourlyEmployee External Agent Customer, Regional Warehouse, e.g. Billing System Rules By Type Process Must have both inputs & outputs At least one output must be different Data Flow Has only one direction Cannot return directly to the process Data must be moved via a process

8 Other Concepts Retrieval Updates Packet Insert Update Delete
Price Inventory Item Item # Price Inventory Item New item Inventory Item Quantity on hand Inventory Item Purged item Inventory Item Student Application & resume Student application When items travel together resume # P1.1 # P1.1

9 DFD Practice Draw a Level-0 Diagram Notes:
Time card ≠ Time sheet Treat “Employee” as external to this system. Employees provide the departmental secretary with their weekly timecards. The secretary prepares a weekly time sheet that lists each employee, the total hours worked, and the hourly rate. The timecards are filed in a Time card history file. The departmental supervisor signs the time sheet if everything seems to be in order. If any figures are unacceptable, the supervisor returns the sheet to the secretary. The acceptable sheets from the departments are sent in the company mail to the accounting department. The accounting clerk uses the acceptable time sheets to calculate payroll earnings and writes the earnings on the time sheets. Another clerk uses the time sheets to prepare the payroll checks, which are forwarded to the employees. After this operation, the time sheets are filed in an off-line Time sheet history file.

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