Process Modeling
Graphically represent the processes that
capture, manipulate, store, and distribute
data between a system and its
environment
Models
DFDs -- Process, Data & Externals
ERDs -- Data Structure -- no Process
Process Logic and Timing
Process Modeling
Deliverables
Context DFD (Not in D/2000)
DFD of current physical system
DFD of current logical system
DFD of new logical system
Adequate descriptions of each DFD
component (Oracle Repository)
DFD Mechanics
Process
Data store
Source/Sink
Data flow
Context Level DFD
Customer
Order
0
Food Order
CUSTOMER
Receipt
Food
Ordering
System
Management
Reports
RESTAURANT
MANAGER
Figure 8.4, p284
KITCHEN
Level Zero (First Level) Diagram
Customer
Order
CUSTOMER
Receipt
1
Goods
Sold
Formatted
Goods
Sold Data
Food Order
Receive &
Transform
Customer
Food Order
KITCHEN
Inventory
Data
2
3
Update
Goods Sold
File
Update
Inventory
File
Formatted
Inventory Data D2
Inventory File
D1
Goods Sold File
Daily Goods Sold Amounts
4
Produce
Management
Reports
Figure 8.5, p285
Daily Inventory Depletion
Amounts
Management Reports
RESTAURANT
MANAGER
DFD Rules -- Process
A. No process can have only outputs
B. No process can have only inputs
Every Process has Input & Output
C. (1) Use Verb phrase labels for the
lowest level (Basic Function
Module - a BFM has no explosion)
(2) Use xxx Process for the others
DFD Rules -- Process
Incorrect
A.
B.
Correct
DFD Rules -- Data Store
D.Data cannot move directly from one data
store to another data store
E.
Data cannot move directly from an outside
source to a data store
F.
Data cannot move directly to an outside sink
from a data store
One end of a Data Flow must be a Process
G.
Use a Noun phrase label (Entity Name)
DFD Rules -- Source / Sink
H.
Data cannot move directly from a
source to a sink. It must be moved by
a process.
I.
Noun phrase label. (External)
Contents are Entities - one Primary
DFD Rules -- Data Flow
J.
K.
L.
A data flow has only one direction of flow
between symbols; a data flow may flow in
both directions to and from a data store
(usually two symbols)
A fork in a data flow means that exactly the
same data goes to two different processes
or data stores.
A join in a data flow means that exactly the
same data comes from two different
processes and data stores.
DFD Rules -- Data Flow
Incorrect
J.
K.
L.
Correct
DFD Rules -- Data Flow
M.
A data flow cannot go directly back to
the same process it leaves
N. A data flow to a data store means
create, update or delete
O. A data flow from a data store means
retrieve or use
P. Use a Noun phrase label. Contents are
attributes of entities and data items
Other DFD Issues
Decomposition (Explosion)
Explode a single process into
subprocesses
Balancing (the Great Circle Rule)
Conserve all process inputs and
outputs when decomposing a
process
Decomposition of 4.0
Daily Goods Sold
Am ounts
4.1
Inventory Data
Access
Daily Inventory
Depletion Am ounts Goods Sold
& Inventory
Data
Goods Sold
Data
4.2
Aggregate
Goods Sold
& Inventory
Data
Aggregated
Data
4.3
Prepare
Managem ent
Reports
Figure 8.8 and 8.7, p289
Managem ent
Reports
Decomposition of 4.3
4.3.2
4.3.1
Aggregated Data
Format
Management
Reports
Figure 8.9, p290
Formatted Data
Print
Management
Reports
Management
Reports
Balance - Context Level
0
Source 1
A
B
System
Sink 1
Unbalanced DFD
1
Source 1
A
C
Source 2
Formatted Formatted
A
C
2
B
Sink 1
DFD Rules -- Advanced
Rules
R. The inputs to a process must be
sufficient to produce the outputs
S. At the lowest level of DFDs, new data
flows may be added to represent data
that are transmitted under exceptional
conditions (e.g., error messages).
T. To avoid having data flow lines cross
each other, you may repeat data stores or
sources / sinks on a DFD.
DFD Guidelines
Completeness
Consistency
Timing
Iterative Development
Primitive DFDs -- BFM
Level
Single database operation - update,
retrieve, create, delete
Single other process function -- input or
output data; calculate; decision
Process for each option or choice
Data flow split to each use set
User and Analyst are satisfied
Element of Personal Choice