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DATA FLOW DIAGRAMS. An Example. DFD 0: Registration System (Context Level). printer. Registration System (A Toy Example). user. P2 Prepare invoice. P4 Print invoice. invoice. invoice_prt. registration. reg+. reg-profile. P1 Read & check reg. prices. registration db.

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slide2

DFD 0: Registration System (Context Level)

printer

Registration System

(A Toy Example)

user

P2

Prepare

invoice

P4

Print

invoice

invoice

invoice_prt

registration

reg+

reg-profile

P1

Read

& check

reg.

prices

registration db

conf_msg

reg_info

reg+

P5

Write

conf.

P3

Accept

reg.

conf.

user

slide3

DFD L1: Registration System

printer

user

P2

Prepare

invoice

P4

Print

invoice

invoice

invoice_prt

registration

reg+

reg-profile

P1

Read

& check

reg.

prices

registration db

conf_msg

reg_info

reg+

P5

Write

conf.

P3

Accept

reg.

error_msg (reg-)

conf.

user

slide4

DFD L2: P1- Read and Check Registration

registration

reg+

P1.1

Read

registration

reg_i

P1.2

Check

registration

reg+

error_reason

P1.3

Error-handler

registration

error_msg (reg-)

remember during composition
Remember during Composition
  • a process should not have

identical inputs and outputs

  • all data flows must be labelled
  • sources / sinks are not processes (=active)
  • data stores should not be connected

directly to sources / sinks

  • there is no timing in a DFD
suggestions for a good style
Suggestions for a Good Style
  • organise diagram from

left to right or top to bottom

  • provide input and output “filters”

for each major data flow

  • keep sources / sinks on the left or right boundary of your diagram
process decomposition interface consistency
Process DecompositionInterface Consistency

o1

P1

i1

i11

o1

f1

p11

i1

p13

f2

i12

f5

f4

p12

local-data

i2

f3

i2

process decomposition
Process Decomposition
  • processes can be decomposed / refined
  • one process ===> complete DFD
  • interface flows must remain consistent
  • lower level processes, data flows

and data stores can be added on

  • sources sinks remain on level-1
  • a level-0 can be used as “abstract”=> Context Level DFD
end of section 2c
End of Section 2c

coming up:

data dictionaries