7 DFD Rules Naming Conventions Rules By Type DFDs should: Processes Accurately represents the systemBe BalancedBe ConsistentBe ReadableNaming ConventionsProcessesVerb phrase = verb + objecte.g. ValidateAccount, CalculateTaxData FlowsNoun/noun phrase = adj + objecte.g. payment, verified paymentData Storese.g. Employee, HourlyEmployeeExternal AgentCustomer, Regional Warehouse, e.g. Billing SystemRules By TypeProcessMust have both inputs & outputsAt least one output must be differentData FlowHas only one directionCannot return directly to the processData must be moved via a process
9 DFD Practice Draw a Level-0 Diagram Notes: Time card ≠ Time sheetTreat “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.