DFD Construction Process

Words to Diagrams

Data Flow Diagrams (DFDs)

Analysis toolSystem modelingExcellent documentation toolData flow, aka, business processProvide a way to see the pattern

Systems Thinking Systems View Systems Approach

Data Flow Diagrams (DFDs) - continued

Advantages for systems view, working with users: Four simple symbols: (1 ) E x te rn a l E n ti ty

- s o u rce an dd es t in a t io n o fd a ta

(2 ) P ro ces s

(3 ) D a ta S to re

(4 ) D a ta F lo w

o r

#

o r

Data Flow Diagrams (DFDs) - continued

Simple rule: left to right, top to bottom, basically (like

English) Show all processes data flows must start or end in a process beware of black holes - every process and data

store must produce data no “magic processes” - must enter all needed

data to get data out

Data Flow Diagrams (DFDs) - continued

* Key: Simple Symbols

Most common error: Trying to do too much

DFD Example

In the following example, a DFD will be created based on a paragraph about Bebop Records Co.’s method of receiving and filling orders.

In this example, the information necessary to create the DFD is provided for us. In Real Life, this information comes from extensive interviewing, document gathering, and other research.

Depending upon the system being studied, the number of people working on it, etc., the development of a detailed DFD can take anywhere from a few hours to several months (paid for by your client with NO CODE TO SHOW FOR IT). Yet it is a very standard and meaningful part of system documentation.

DFD ExampleBebop Records is a mail-order company that distributes CDs and tapes at discount price to record-club members. When an order processing clerk receives an order form, he or she verifies that the sender is a club member by checking the Member file. If the sender is not a member, the clerk returns the order along with a membership application form. If the customer is a member, the clerk verifies the order item data by checking the Item file. Then the clerk enters the order data and saves it to the Daily Orders file. The clerk also prints an invoice and shipping list for each order, which are forwarded to Order Fulfillment.

DFD Example - Step 1

FIRST SENTENCE:

Bebop Records is a mail-order company that distributes CDs and tapes at discount price to record-club members.

RESULT: initial title

Bebop Records

DFD Example - Step 2

SECOND SENTENCE:

When an order processing clerk receives an order form, he or she verifies that the sender is a club member by checking the Member file.

RESULT:

Bebop Records Order Processing

EE-1

R e c o rd C lu bM e m b e r

1

Verify m em bers tatus

O R Clerk

EE-2

C u s t o m e r(n o n -m e m b e r)

D -1 M e m b e r M a s t e ro rd e r m e m b e rd a t a

DFD Example - Step 2 continued

SECOND SENTENCE:

When an order processing clerk receives an order form, he or she verifies that the sender is a club member by checking the Member file.

RULES FOLLOWED: left to right, top to bottom data flows start or end in a process

DFD Example - Step 3

THIRD SENTENCE:

If the sender is not a member, the clerk returns the order along with a membership application form.

RESULT:

Bebop Records Order Processing

EE-1

R e c o rd C lu bM e m b e r

1

Verify m em bers tatus

O R Clerk

EE-2

C u s t o m e r(n o n -m e m b e r)

D -1 M e m b e r M a s t e ro rd e r m e m b e rd a t a

n o n -m e m b e r o rd e ra n d a p p lic a t io n fo rm

DFD Example - Step 3 continued

THIRD SENTENCE:

If the sender is not a member, the clerk returns the order along with a membership application form.

RULES FOLLOWED: shows all processes without conditions

DFD Example - Step 4

FOURTH SENTENCE:

If the customer is a member, the clerk verifies the order item data by checking the Item file.

RESULT:

Bebop Records Order ProcessingEE-1

R e c o rd C lu bM e m b e r

1

Verify m em bers tatus

O R Clerk

EE-2

C u s t o m e r(n o n -m e m b e r)

D -1 M e m b e r M a s t e ro rd e r m e m b e rd a t a

n o n -m e m b e r o rd e ra n d a p p lic a t io n fo rm

2

Verify orderitem data

O R Clerk

m e m b e ro rd e r

D -2 It e m M a s t e rit e md a t a

DFD Example - Step 4 continued

FOURTH SENTENCE:

If the customer is a member, the clerk verifies the order item data by checking the Item file.

RULES FOLLOWED: left to right, top to bottom data flows start or end in a process shows all processes without conditions

DFD Example - Step 5

FIFTH SENTENCE:

Then the clerk enters the order data and saves it to the Daily Orders file.

RESULT:

DFD Example - Step 5 continued

RESULT: Bebop Records Order Processing

EE-1

R e c o rd C lu bM e m b e r

1

Verify m em bers tatus

O R Clerk

EE-2

C u s t o m e r(n o n -m e m b e r)

D -1 M e m b e r M a s t e ro rd e r m e m b e rd a t a

n o n -m e m b e r o rd e ra n d a p p lic a t io n fo rm

2

Verify orderitem data

O R Clerk

m e m b e ro rd e r

D -2 It e m M a s t e rit e md a t a

3

Enter orderin to D aily

O rders

O R Clerk

v e rifie dm e m b e r

o rd e r

D -3 D a ily O rd e rs D e t a ilo rd e r

DFD Example - Step 5 continued

FIFTH SENTENCE:

Then the clerk enters the order data and saves it to the Daily Orders file.

RULES FOLLOWED: left to right, top to bottom data flows start or end in a process

DFD Example - Step 6

SIXTH SENTENCE:

The clerk also prints an invoice and shipping list for each order, which are forwarded to Order Fulfillment.

RESULT:

DFD Example - Step 6 continuedRESULT:

Bebop Records

Order Processing

EE-1

R e c o rd C lu bM e m b e r

1

Verify m em bers tatus

O R Clerk

EE-2

C u s t o m e r(n o n -m e m b e r)

D -1 M e m b e r M a s t e ro rd e r m e m b e rd a t a

n o n -m e m b e r o rd e ra n d a p p lic a t io n fo rm

2

Verify orderitem data

O R Clerk

m e m b e ro rd e r

D -2 It e m M a s t e rit e md a t a

3

Enter orderin to D aily

O rders

O R Clerk

v e rifie dm e m b e r

o rd e r

D -3 D a ily O rd e rs D e t a ilo rd e r

4

P rin t invoic eand

s hipping lis t

O R Clerk

o rd e rd a t a

EE-3

O rd e rF u lfillm e n t

in v o ic e a n ds h ip p in g lis t

DFD Example - Step 6 continued

SIXTH SENTENCE:

The clerk also prints an invoice and shipping list for each order, which are forwarded to Order Fulfillment.

RULES FOLLOWED: left to right, top to bottom data flows start or end in a process shows all processes without conditions beware of black holes - every process and data store must

produce data

Individual Homework Assignment

All Villanova students have gone through the admission process in order to become an enrolled member of the student body. As you think back on the admissions “process” there was a variety of information that was required in order to accept you as a student.

For this assignment, you are to create a context diagram and a 1st level decomposition of the admission process. Be sure you understand the “system boundary”, use proper symbols, and represent all of the information needed by the admissions department.

The Admissions web site is a good place to start if you don’t remember everything you did when you applied.

http://www.villanova.edu/enroll/admission/