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Part 1: Data Flow Diagramming. Supplement to Chapter 2. Data Flow Diagramming. Represent processes …that capture, manipulate, store, & distribute data …between a system & its environment … & among system components. Data Flow Diagramming. a process modeling technique. Data Store. #.
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Part 1: Data Flow Diagramming Supplement to Chapter 2
Data Flow Diagramming • Represent processes • …that capture, manipulate, store, & distribute data • …between a system & its environment • … & among system components.
Data Flow Diagramming • a process modeling technique Data Store # # Process Source input retrieval storage output Sink Show that data flow continues to another process 2.0 Connector
Order Entry System Context Diagram • An overview • Represents the System Scope Customers Sales orders Accepted sales order file Rejected sales order report 0 Inventory System President
Level-0 Diagram Customers Master item number list Sales orders Item numbers 1.0 Item prices Master price list Screen sales orders 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 President
Level 1 Diagram (for Process 1.0)aka: Diagram 1.0 Sales orders Customers 1.1 Verify item number Master item number list Master item number list Item numbers Verified item numbers Accepted sales order file 1.2 Inventory System Verify price Item prices Master price list Master price list Rejected sales order file 2.0
DFD Rules • 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 • Noun/noun phrase = adj + object • e.g. Employee, HourlyEmployee External Agent • Noun/noun phrase = adj + object • 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 • DFDs should: • Accurately represents the system • Be Balanced • Be Consistent • Be Readable
Other Concepts • Retrieval • Updates • Insert • Update • Delete • Packet Price Item # # # Inventory Item Inventory Item Inventory Item Inventory Item Inventory Item P1.1 P1.1 Quantity on hand Purged item New item Price Student Application & resume Student application When items travel together resume
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.
