IMS 5024 Semester 2, 2002 Lecture 3

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IMS 5024

Process Modelling

IMS 5024 Semester 2, 2002 Lecture 3

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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

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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?

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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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Symbols

Process

Internal/external entity

Data store

Data flow

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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)

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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

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Reading for next week

Simsion, G. (1994). Data modeling essentials: Analysis, Design, and Innovation. Van Nostrand Reinhold, USA. Chapter 2, 7 and 10.