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IMS 5024 Semester 2, 2002 Lecture 3
2
Content
Hand in Synopsis Class assignment Nature of process modelling Abstraction Tools/Techniques used in process modelling Place in ISD Evaluation of process modelling Reading list
IMS 5024 Semester 2, 2002 Lecture 3
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Class assignment
What is this about?
What conventions/rules are used?
What does it depict?
Where would this fit into ISD?
IMS 5024 Semester 2, 2002 Lecture 3
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Process modelling help us to grasp:
InputsOutputsProcessingRelationship between
processes
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Abstraction
Def: Stripping and idea or system of its concrete and physical features (Avison et. Al.)
Show essence!! Level of abstraction
– High– Low
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Levels of DFD’s
Context DFD Decomposition diagram Overview DFD (system DFD) Middle level DFD Primitive level DFD
Link to other techniques?
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Example Context Diagram
InventorySystem
SuppliersSales Order
System
Warehouse
sales order
goods unavailable notice
purchase order
supplier delivery
shipping slip checked supplierinvoice
AccountsDepartment
goods returned
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Tools used
Data flow diagrams Decomposition diagram Data Dictionary Structured English Decision Tables Decision Trees
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Data dictionary entry examplesales order = sales order no. +
sales order date +customer number +[account customercash customer] +customer name +customer address +(customer telephone no) +{order item} +sales order total amount
order item = item no + item desc +item price +item qty
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Accept sales-orderFind customer-detailsIf customer-details not found
Then reject sales-orderElse
Create sales-order-headerDo while more sales-order-items
find item-detailscalculate sales-order-item price = item price
*order-qtyEndoAuthorise sales-order
Endif
Example Structured English
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Example Decision Table
avg account bal > $1,000
overdraft amount < $50,000previous paid-out loan
approve
conditional approval
reject
Y Y Y Y N N N N
Y Y N N Y Y N N
Y N Y N Y N Y N
X X
X
X
X
X X X
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Decision Trees
wholesalecustomer
retailcustomer
local item
local item
imported item
imported itemDetermine Customer Discount
15%
10%
12%
7%
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Example Function Decomposition Diagram
ABC Sales System
1. Sell Products
2. Manage Inventory
3. Control Finance
2.1 Deliver Product
2.2 Accept Delivery
2.3 CheckStock levels
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Rules to guide the modelling
Levelling – two waysExpand Explode
Balancing Naming conventions Always input and output No direct dataflow between data store and entity Number of processes on a level Numbering conventions
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Context diagram
Levelling DFDs
3.1
3.2
Diagram 3 (level 1)
12
3
Level zero diagram
2.1
2.2
Diagram 3 (level 1)Further diagrams or process descriptions
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Different levels of modelling
Conceptual level – Not confuse with conceptual modelling of data
Logical level Physical level Where does DFD’s fit into this?
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Deliverables for process modelling is used
Old New
Physical
Logical
1
2 3
4
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Validation of the model
Walkthroughs with user Validate for:
– Missing algorithms– Logical verification– Syntax Checking– Tracing data elements– Cross referencing– Tracing objectives
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Reality of ISD
Conceptual models
Formal Models
Application domain
Implementation domain
Blum, I., 1994. A taxonomy of Software development Methods. Communications of the ACM, Vol37, No11
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Evaluation of Process modelling
Problem oriented Product oriented
Concep-tual
Structured analysis
Entity relationship modelling
Logical construction of systems
Modern structured analysis
Object oriented analysis
Structured design
Object oriented design
Formal PSL/PSA
JSD
VDM
Levels of abstraction
Stepwise refinement
Proof of correctness
Data abstraction
JSP
Object oriented programming
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Thinking in Process modelling
Hard Vs Soft ?? Perspective
– Objective vs Subjective– Nature of the organisation
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Advantages of Process modelling
a well-known process modelling ISD 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
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Disadvantages
Focus on processes – need to know a lot to get a good understanding
Miss key aspects of the data Others??
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Process modelling view of ISD
Development group
Objectives
Environment
Object system
ObjectsystemChange
process
Hirschheim et al see reading list
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Classification of methodsProblem oriented Product oriented
Concep-tual
Structured analysis
Entity relationship modelling
Logical construction of systems
Modern structured analysis
Object oriented analysis
Structured design
Object oriented design
Formal PSL/PSA
JSD
VDM
Levels of abstraction
Stepwise refinement
Proof of correctness
Data abstraction
JSP
Object oriented programming
Blum, I., 1994. A taxonomy of Software development Methods. Communications of the ACM, Vol37, No11