Rules_DFD
(052814)
General Application Rules Chart:
NAME
SYMBOL
RULES
LABELS/NUMBER
REQUIRED ENTRY
Process
Each process is unique,
DFDs decompose on
processes
Unique name (once
per project) and
number
Diagram and
Description
Stored Data
Can be nested or reused,
Represent the mass logical
data stores (MLOG/LOG)
Unique name (once
per project)
Description and
MLOG/LOG
Entity
Must be reused,
Unique name (once
Entities represent teams of
per project)
individuals/function providers.
Description
Data flow
Each data flow is unique,
Nested, but not modeled.
Each line has two
Labels. One way linear
relationship are rare!
DFDs with ATOMIC
PROCESSES require a
data flow table
Unique name (once
per project), No label
required for linear
relationship.
For our projects we only label the data flows at the atomic (bottom) level. Data flow in many of
the software tools will actually show two separate lines to and from. In almost every instance a
query (question is asked) and a response is given. A one way arrow could represent a process
like issuing a W-2 tax notice where the employee does not acknowledge receipt, or a donation
in a kettle during the holidays in front of a store.
Any DFD containing an Atomic process requires a data flow table showing every data flow on
the DFD.
Entities and data stores can be shown multiple times on a single DFD.