1 DATA FLOW DIAGRAMS An Example

2 registration P1 Read & check reg. P2 Prepare invoice P3 Accept reg. P4 Print invoice P5 Write conf. user printer registration db reg+ reg_info conf. invoice reg- profile prices invoice_prt conf_msg DFD 0: Registration System (Context Level) error_msg Registration System (A Toy Example)

3 registration P1 Read & check reg. P2 Prepare invoice P3 Accept reg. P4 Print invoice P5 Write conf. user printer registration db reg+ reg_info conf. invoice reg. profile prices invoice_prt conf_msg error_msg DFD L1: Registration System

4 P1.1 Read registration P1.2 Check registration P1.3 Error-handler registration reg+ error_code error_msg reg_data Level 2 of P1 “Read and Check Registration”

5 Remember during Composition a process should not have identical inputs and outputs all data flows must be labelled sources / sinks are not processes (=active) data stores should not be connected directly to sources / sinks there is no timing in a DFD

6 Suggestions for a Good Style organise diagram from left to right or top to bottom provide input and output “filters” for each major data flow keep sources / sinks on the left or right boundary of your diagram

7 Process Decomposition Interface Consistency P1 i1 i2 o1 p11 p12 p13 local-data i11 i12 i2 o1 i1 f1 f2 f3 f4 f5

8 Process Decomposition processes can be decomposed / refined one process ===> complete DFD interface flows must remain consistent lower level processes, data flows and data stores can be added on sources sinks remain on level-1 a level-0 can be used as “abstract”=> Context Level DFD

9