Process Modeling

1
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

2
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)

3
DFD Mechanics
4
Context Level DFD
Figure 8.4, p284
5
Level Zero (First Level) Diagram
Figure 8.5, p285
6
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

7
DFD Rules -- Process
Incorrect Correct
A. B.
8
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)

9
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

10
DFD Rules -- Data Flow

• J. 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)
• K. A fork in a data flow means that exactly the
  same data goes to two different processes or
  data stores.
• L. A join in a data flow means that exactly the
  same data comes from two different processes
  and data stores.

11
DFD Rules -- Data Flow
Incorrect Correct
J. K. L.
12
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

13
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

14
Decomposition of 4.0
Figure 8.8 and 8.7, p289
15
Decomposition of 4.3
Figure 8.9, p290
16
Balance - Context Level
0
System
B
A
Sink 1
Source 1
17
Unbalanced DFD
1
A
Source 1
C
Formatted A
Formatted C
Source 2
2
Sink 1
B
18
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.

19
DFD Guidelines

• Completeness
• Consistency
• Timing
• Iterative Development

20
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