IMS 5024
Process Modelling
IMS 5024 Lecture 3 1
Content
Group assignment
Class assignment
Nature of process modelling
Abstraction
Tools/Techniques used in process modelling
Place in ISD
Evaluation of process modelling
Reading list
IMS 5024 Lecture 3 2
Class assignment
What is this about?
What conventions/rules are used?
What does it depict?
Where would this fit into ISD?
IMS 5024 Lecture 3 3
Process modelling help us to
grasp:
Inputs
Outputs
Processing
Relationship between
processes
IMS 5024 Lecture 3 4
Abstraction
Def: Stripping and idea or system of its
concrete and physical features (Avison
et. Al.)
Show essence!!
Level of abstraction
– High
– Low
IMS 5024 Lecture 3 5
Levels of DFD’s
Context DFD
Decomposition diagram
Overview DFD (system DFD)
Middle level DFD
Primitive level DFD
Link to other techniques?
IMS 5024 Lecture 3 6
Example Context
Diagram
Sales Order sales order purchase order
System Suppliers
goods returned
supplier delivery
goods unavailable Inventory
notice System
shipping slip checked supplier
invoice
Accounts
Department
Warehouse
IMS 5024 Lecture 3 7
Tools used
Data flow diagrams
Decomposition diagram
Data Dictionary
Structured English
Decision Tables
Decision Trees
IMS 5024 Lecture 3 8
Symbols
Process
Internal/external entity
Data store
Data flow
IMS 5024 Lecture 3 9
Data dictionary entry example
sales order = sales order no. +
sales order date +
customer number +
[account customer
cash customer] +
customer name +
customer address +
(customer telephone no) +
{order item} +
sales order total amount
order item = item no +
item desc +
item price +
item qty
IMS 5024 Lecture 3 10
Example Structured English
Accept sales-order
Find customer-details
If customer-details not found
Then reject sales-order
Else
Create sales-order-header
Do while more sales-order-items
find item-details
calculate sales-order-item price = item price *order-
qty
Endo
Authorise sales-order
Endif
IMS 5024 Lecture 3 11
Example Decision Table
avg account bal >
$1,000 Y Y Y Y N N N N
overdraft amount
Y Y N N Y Y N N
< $50,000
previous paid-out Y N Y N Y N Y N
loan
approve X X
conditional X X
approval
reject X X X X
IMS 5024 Lecture 3 12
Decision Trees
local item 15%
wholesale
customer
imported item 10%
local item 12%
retail
customer
Determine Customer Discount
imported item 7%
IMS 5024 Lecture 3 13
Example Function
Decomposition Diagram
ABC Sales
System
1. Sell 2. Manage 3. Control
Products Inventory Finance
2.1 Deliver 2.2 Accept 2.3 Check
Product Delivery Stock levels
IMS 5024 Lecture 3 14
Rules to guide the modelling
Levelling – two ways
Expand Explode
Balancing
Naming conventions
Always input and output
No direct dataflow between data store and entity
Number of processes on a level
Numbering conventions
IMS 5024 Lecture 3 15
Levelling DFDs
1
2
Context diagram 3
Level zero diagram
2.1
3.1
2.2
3.2
Further diagrams or 3 Diagram 3 (level 1)
Diagram 3 (level 1) IMS 5024 Lecture 16
process descriptions
Different levels of modelling
Conceptual level – Not confuse with
conceptual modelling of data
Logical level
Physical level
Where does DFD’s fit into this?
IMS 5024 Lecture 3 17
Deliverables for process
modelling is used
Old New
4
1
Physical
Logical
2 3
IMS 5024 Lecture 3 18
Verification of the model
Walkthroughs with user
Verify for:
– Missing algorithms
– Logical verification
– Syntax Checking
– Tracing data elements
– Cross referencing
– Tracing obejctives
IMS 5024 Lecture 3 19
Evaluation of Process modelling
Problem oriented Product oriented
Concep- Structured analysis Structured design
tual Entity relationship Object oriented design
modelling
Logical construction of
systems
Modern structured analysis
Object oriented analysis
Formal PSL/PSA Levels of abstraction
JSD Stepwise refinement
VDM Proof of correctness
Data abstraction
JSP
IMS 5024 Lecture 3 20
Object oriented programming
Thinking in Process modelling
Hard Vs Soft ??
Perspective
– Objective vs Subjective
– Nature of the organisation
IMS 5024 Lecture 3 21
Advantages of Process modelling
a well-known process modelling technique
easily understood
a good communication tool
model both manual and automated processes
shows relationship between data and
processes
Excellent tool for logical level discussions
Supported by a number of CASE tools
IMS 5024 Lecture 3 22
Disadvantages
Focus on processes – need to know a
lot to get a good understanding
Miss key aspects of the data
Others??
IMS 5024 Lecture 3 23
Process modelling view of ISD
Development Objectives
group
Object
Object system
Change
system process
Hirschheim et al see reading list Environment
IMS 5024 Lecture 3 24
Blum, I., 1994. A taxonomy of Software development Methods. Communications of the ACM, Vol37, No11
Classification of methods
Problem oriented Product oriented
Concep- Structured analysis Structured design
tual Entity relationship Object oriented design
modelling
Logical construction of
systems
Modern structured
analysis
Object oriented analysis
Formal PSL/PSA Levels of abstraction
JSD Stepwise refinement
VDM Proof of correctness
Data abstraction
JSP
Object oriented
IMS 5024 Lecture 3 25
programming
Reading for next week
McFadden, F.R.; Hoffer, F.R; Prescott,
M.B. (1999). Modern Database
Managemetn. Fifth Edition. Addison
Wesley, USA. Chapter 3 and 4.
IMS 5024 Lecture 3 26