1. 06 Data Flow Diagrams - Exploding
And Franchise Colleges
06 Data Flow Diagrams - Exploding
By MANSHA NAWAZ
Section 06
DFD - Exploding

2. Learning Aims Aim Objectives
to be able to explode a process on a top-level DFD
Objectives
to distinguish primitive/non primitive processes
to identify appropriate sub-processes
to identify local data stores
to construct the exploded DFD consistent with the parent DFD
Section 06
DFD - Exploding

3. Lecture Outline selecting processes for exploding
initial inputs and outputs
identifying sub-processes
local data stores
diagram construction
consistency checking
diagram hierarchy
Section 06
DFD - Exploding

4. Checking Processes on the DFD
check each process, can it be broken down into meaningful sub-processes? no
a functional primitive
do not explode
yes
explode the process Q 3
enter
order 1
check
stock þ
Section 06
DFD - Exploding

5. Inputs & Outputs to Explosions
each exploded process has its own inputs and outputs
the data flows into the process must all appear as inputs to the exploded process
the data flows out of the process must all appear as outputs from the exploded process
Section 06
DFD - Exploding

6. Modelling Sub-processes
the task is to identify all the sub-processes that must take place to achieve the purpose of the parent process
start by identifying the normal sequence of events
list the processes
identify the error or abnormal events
add to the process list
Section 06
DFD - Exploding

7. Local Data Stores
it may become apparent that a new data store is required
if only the sub-processes interface with it then add it to the exploded diagram
if other processes use it, add to the top level
if a data store on the top level DFD only interfaces with one process
remove it and place inside the exploded process
Section 06
DFD - Exploding

8. Diagram Construction
the exploded process is represented by a large frame, named and numbered
on the left outside are placed the inputs
on the right outside are placed the outputs
sub-processes & local data stores are placed inside the frame
Section 06
DFD - Exploding

9. Contd. add the processes connecting them to the in/outputs
numbering the processes
n.1, n.2 etc where n is the number of the parent
numbering the data stores
continue the sequence from the top level
make sure all inputs & outputs are connected to the sub-processes
Section 06
DFD - Exploding

10. Consistency Checking check numbering correct check no name clashes
check number of inputs and outputs are at least as many as those on the top level
if there are more check they are logically the same
flow duplication and splitting is possible
Section 06
DFD - Exploding

11. Diagram Hierarchy
it is possible to explode the processes in an exploded diagram
this leads to a hierarchy of levelled DFDs
Section 06
DFD - Exploding

12. Development : Low-Level DFD
Low-Level Data Flow Diagram (LL-DFD)
For each process
Low-Level DFD description
Low-Level DFD Diagram
Top-Level Data Flow Diagram (TL-DFD)
Amend your diagrams and supporting text after consistency checking with the low-level DFD’s.
Top-Level DFD description
Top-Level DFD Diagram
Context Diagram (CD-DFD)
Context Diagram description
Context Diagram
Section 06
DFD - Exploding

13. Document : Analysis Specification
Terms Of Reference lecture 02
Context Diagram lecture 03
Top-Level Data Flow Diagram lecture 04
Top-Level DFD Support Text lecture 05
Top-Level DFD lecture 06
Data Flow Fragments
Low-Level Data Flow Diagrams lecture 06 lecture 07
For each Top-Level process
Low-Level DFD Support Text
Low-Level DFD
Section 06
DFD - Exploding

14. Summary & Self Study Summary check processes capture in/outputs
check local data stores
build DFD
check consistent
levelled hierarchy
Self Study
review the lecture
complete 6a from the workbook
can you achieve the objectives set out in slide 2?
Section 06
DFD - Exploding

15. … see what you can utilise from the following guides
Further Reading
There are many ways to develop a proposed computer system model
… see what you can utilise from the following guides
Guide to documenting DFDs using Toy Sales Order Example
Toy Sales Ordering System
Guide to modelling multilayered systems
DFD Review 1
Guide to modelling basic systems
DFD Review 2
Common Functions, Features, Events and Sub-Events
SOP
Common Functions, Features, Events and Sub-Events from PowerQuotes Case Study
powerquote
Sample DFD Models
Ascent Solutions
Section 06
DFD - Exploding

16. Further Reading Notes from Annette Marshall
Section 06
DFD - Exploding