Data Flow Diagramming 1

Used to represent processes that:  … capture, manipulate, store, & distribute data  … between a system & its environment  … & among system components. It's a Process Modeling technique!

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

Context Diagram An overview; represents the System Scope 4 Order Entry System Customers Inventory System Sales Manager Sales orders Accepted sales order file Rejected sales order report Reject notice 1010

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

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

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

Balancing! Level 1 Diagram (Process 1.0) Level 0 Diagram Context Diagram Level 1 Diagram (Process 2.0)

Consistency! Level 0 DiagramContext Diagram Watch out for inconsistent names!

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 10 DFDs should: Accurately represents the system Be Balanced Be Consistent Be Readable

Other Concepts Retrieval Updates  Insert  Update  Delete Packet 11 New item Inventory Item Quantity on hand Inventory Item Purged item Inventory Item Price Inventory Item Price Inventory Item Item # # P1.1 application Student resume # P1.1 Application & resume Student When items travel together