ISMT221 Information Systems Analysis and Design Advanced Data Flow Diagram Lab 3 Tony Tam

Rules on DFD – complete and consistent Complete All elements must be drawn and included properly Consistent Balance - all inputs and outputs must be conserved in each level Each levels are compatible

Process No miracle No black hole Inputs should differ from outputs

Data Store I Cannot move from data store to data store Cannot move from external entity to data store

Data Store II Cannot move from data store to external entity

External Entities Cannot move from source to sink directly 1. We care flow within our system (need process) 2. We don’t care flow external to our system (why bother?)

Data Flow I Data flow is one direction (no unidirectional) A fork (split) must have exactly same data

Data Flow II A join must have exactly same data Data flow cannot go back to same process it leaves. There must be another process to handle it before going back (a self-contained system?)

General I Data flow in higher level can split in lower level; but all data must be accounted for in each subflow Level-0Level-1

General II No grey hole – input and output must be appropriate