Transcript Vocabulary of DFDs - Indiana University

Logical Dataflow Diagrams
(DFDs)
Vocabulary of DFDs
Context
DFD
Bubble
Square
Physical
DFD
Logical
DFD
The
System
Internal
Entity
Process
External
Entity
External
Entity
External
Entity
N/A
File
File
Data
Flow
Data
Flow
or
“connector”
Data
Flow
Guidelines for DFDs
• The idea is that we would like to group activities
that “belong together” into processes.
• Note that a process is a just set of related
activities.
• The SYSTEM itself is just a set of activities, too.
• There are no ENTITIES now.
Guidelines for DFDs
• The approach is easy – Sort the list of activities chronologically - I usually just
write down the numbers in chronological order (we
actually already did this)
– Break it into processes by deciding upon “division points”
between processes. This is TOTALLY up to you. There
is not necessarily a right answer. The only rule is that
every process must have at least ONE activity.
– Write F over each number that is a file activity and E
over each number that is a data flow to or from an
external entity. Do not worry about data flows between
internal entities.
Guidelines for DFDs
An Example - Causeway
E
F F F
E
F
E
1, 2, 3, 4, 5, 6, 7, 8, 17, 13, 14, 15, 16, 11, 12, 18, 19, 9, 10
Guidelines for DFDs
• You would decide how many processes there were by
intuition (but you do not need to worry about that for this
class). For real life situations, the general rule of thumb is
5 to 7 bubbles. You will typically have between 3 and 4 for
this class.
• There would be one bubble for each process and they would
be numbered 1.0, 2.0, 3.0, etc. (again, these will be given for
this class).
• Draw arrows from bubble 1.0 to bubble 2.0 and from bubble
2.0 to 3.0, etc. THESE WILL NOT BE LABELED.
• Draw necessary arrows to and from the “appropriate bubble”
to and from (1) external entities and (3) files.
Causeway
1
Checks
& R/As
Customers
1.0
Open
Mail
2.0
Record
A/R
14
Acc Rec.
G/L
Office
10
4.0
Complete
Cash
Receipts
17
13
Txn Data
3.0
Prepare
Deposit
18
Deposit
Total of C/R
E
F F F
E
F
E
1, 2, 3, 4, 5, 6, 7, 8, 17, 13, 14, 15, 16, 11, 12, 18, 19, 9, 10
12
Bank