DATA FLOW DIAGRAMMING Data Flow Diagramming v Used

DATA FLOW DIAGRAMMING

Data Flow Diagramming v Used to represent processes that: • … capture, manipulate, store, & distribute data • … between a system & its environment • … & among system components.

Data Flow Diagramming Source input retrieval # Data Store storage Process output 2. 0 Connector Show that data flow continues to another process Sink 3

Context Diagram v An overview - shows the relationship between the external agents and the system Customers Sales orders Reject notice Accepted sales order file Inventory System 0 Order Entry System Rejected sales order report Sales Manager 4

Level-0 Diagram v Shows the decomposition of the main system into its major processes & the data that flows between them. Customers Sales orders This diagram can include data stores. For our project, only include data stores that are shared between the major processes. Otherwise, this diagram will get too busy! 1. 0 Reject notice Accepted sales order file Inventory System Screen sales orders 3. 0 Prepare rejected sales order report Rejected sales order file Sorted rejected sales order file Rejected sales order report 2. 0 Sort rejected sales order file Sales Manager

Level 1 Diagram (for Process 1. 0) aka: Diagram 1. 0 Customers Sales orders 1. 1 Verify item number Item numbers Master item Master number list Verified item numbers Reject notice 1. 2 Item prices Inventory System Accepted sales order file Verify price Rejected sales order file 2. 0 Masterprice Master list

DFD Practice Draw a Level-0 Diagram • Notes: o o 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. 7

Balancing! Level 1 Diagram (Process 1. 0) Context Diagram 0 Level 0 Diagram Level 1 Diagram (Process 2. 0)

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

DFD Rules v Naming Conventions Processes o o Verb phrase = verb + object e. g. Validate. Account, Calculate. Tax DFDs should: Accurately represent the system Be Balanced Be Consistent Be Readable Data Flows o o Noun/noun phrase = adj + object e. g. payment, verified payment v Rules By Type Process Data Stores o o Noun/noun phrase = adj + object e. g. Employee, Hourly. Employee External Agent o o Noun/noun phrase = adj + object Customer, Regional Warehouse, e. g. Billing System Must have both inputs & outputs At least one output must be different Data Flow o o Has only one direction Cannot return directly to the process Data must be moved via a process 10

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