14-11-2012, 01:55 PM
DATA FLOW DIAGRAMS
DFD Diagrams.doc (Size: 442 KB / Downloads: 24)
FLOWDIAGRAMSWHAT ARE DATA FLOW DIAGRAMS?
DFDs models the system by depicting
•External entities from which the data flows and where results terminate
•Processes which transform data flows
•Data stores from which the data are read or into which data are written by the processes.
RULES OF DATA FLOW
•Data can flow from-external entity to process-process to external entity-process to store and back-process to process
•Data cannot flow from-external entity to external entity-external entity to store-store to external entity-store to store
GOOD STYLEIN DRAWING DFD
•Use meaningful names for data flows, processes and data stores.
•Use top down development starting from context diagram and successively leveling DFD
•Only previously stored data can be read
•A process can only transfer input to output. It cannot create new data
•Data stores cannot create new dataV