Software System Engineering

1. Chapter 2
Software Development
Models
SOFTWARE SYSTEM
ENGINEERING (260CT)
November 5, 2014 1

2. MMoottiivvaattiioonn//OObbjjeeccttiivvee
To distinguish the differences from
another model to another
To understand the importance of process
in the development of software.
November 5, 2014 2

3. SSooffttwwaarree DDeevveellooppmmeenntt MMooddeellss
Software lifecycle models identify the
key activities in the development of a
software system and their relationships to
one another.
November 5, 2014 3

4. MMooddeellss ddiissccuusssseedd::
 Linear Sequential Model/Waterfall Model
 Prototyping
 RAD Model
 Evolutionary Software Process Models
• The Incremental Model
• The Spiral Model
• The WINWIN Spiral Model
• The Component Assembly Model
• The Concurrent Development Model
November 5, 2014 4

5. LLiinneeaarr SSeeqquueennttiiaall//WWaatteerrffaallll
MMooddeell
 The Waterfall Model was originally developed in the
early 1970s in an attempt to provide some structure to
large-scale software development
 The mother of all software engineering models
 Divided into distinct phases
 Recognizes the importance of backtracking (feedback)
and iteration in the software process
November 5, 2014 5

6. LLiinneeaarr SSeeqquueennttiiaall//WWaatteerrffaallll MMooddeell
Problem encountered:
• Real projects rarely follow the sequential flow
that the model proposed
• It is often difficult for the customer to state all
the requirement explicitly
• The customer must have patience
November 5, 2014 6

7. November 5, 2014 7

8. AAddvvaannttaaggeess
 It is easy to identify milestones
 It is easy to separate one stage from another
November 5, 2014 8

9. DDiissaaddvvaannttaaggeess
 Implies that any stage should be frozen before continuing
with the later stages (resulting in premature requirements,
design, coding etc)
 Assumes that user requirements can be precisely
specified.
 Requires customer to be patient as no way they can
assessing how far the development process has got until
they sees the nearly-finished product
 Unrealistic.
November 5, 2014 9

10. PPrroottoottyyppiinngg
 Suitable for unclear projects.
 Pros:
· identifying requirements
· users get a feeling for the system
· developers get to "do something"
 Cons:
· customer demands working product too early
· bad solutions will remain: throw-away or not?
November 5, 2014 10

11. Definition
“Limited, working version of a system
under development”
November 5, 2014 11

12. Prototyping Paradigm
November 5, 2014 12

13. Types of prototyping
Evolutionary prototyping
Throw-away prototyping
November 5, 2014 13

14. Evolutionary Prototyping
Starts with those requirements that are
well understood
November 5, 2014 14

15. Throw away prototyping
Starts with those requirements that are
poorly understood
November 5, 2014 15

16. Prototyping techniques
High level languages
Executable specification languages
Composition of reusable components
Application generators and forth-generation
languages
November 5, 2014 16

17. Advantages of prototyping
Changing the system early in its
development
Scrapping undesirable systems
Designing a systems for user’s needs
and expectations
November 5, 2014 17

18. Disadvantages of prototyping
Managing the project
Adopting an incomplete system as
complete
November 5, 2014 18

19. RRAADD MMooddeell
 Suitable for projects with low technical risks
 Emphasize on an extremely short development cycle.
 RAD is a methodology for compressing the analysis, design,
build, and test phases into a series of short, iterative
development cycles
 Pros:
· Speed.
· Reuse.
 Cons:
· Requires many developers.
· Requires committed developers.
November 5, 2014 19

20. RRAADD MMooddeell……ccoonntt
November 5, 2014 20

21. EEvvoolluuttiioonnaarryy SSooffttwwaarree PPrroocceessss
MMooddeellss
The Incremental Model
The Spiral Model
WINWIN Spiral Model
The Component Assembly Model
The Concurrent Development Model
November 5, 2014 21

22. TThhee IInnccrreemmeennttaall MMooddeell
 Suitable for products that can be developed in increments.
 Combines elements of linear sequential model with the iterative
philosophy of prototyping
 Pros:
· resolves changing/unclear requirements
· possible to meet business deadlines with little staff
· management of technical risks
 Cons:
· untried?
· building in bad solutions
November 5, 2014 22

23. TThhee IInnccrreemmeennttaall MMooddeell……ccoonntt
November 5, 2014 23

24. TThhee SSppiirraall MMooddeell
 Suitable for large-scale projects.
 Pros:
·prototyping at any stage
·risk reduction as risk analysis is performed
at each phase of system development
·Increases the quality of the software
developed
 Cons:
·suitable for internal or in-house
development of large software
·risk assessment expertise required
November 5, 2014 24

25. TThhee SSppiirraall MMooddeell
November 5, 2014 25

26. WWIINNWWIINN SSppiirraall MMooddeell
 Extension from Spiral Model
 Evolutionary and risk-driven
 Anchor points as milestones
 Theory W – ‘Make everyone a winner’
 Stakeholders
• Customers and Users
• Developers, maintainers and contractors
• Management and investors
 Achieving WINWIN
• Negotiation and Prioritization
November 5, 2014 26

27. WWIINNWWIINN SSppiirraall MMooddeell
November 5, 2014 27

28. TThhee CCoommppoonneenntt AAsssseemmbbllyy
MMooddeell
 Suitable for component-based technologies such as OO.
 Pros:
·software reuse
·reductions in cycle time
·lower project costs
 Cons:
·Finding components
·Are components reusable?
·Adaptation
November 5, 2014 28

29. TThhee CCoommppoonneenntt AAsssseemmbbllyy MMooddeell
November 5, 2014 29

30. TThhee CCoonnccuurrrreenntt DDeevveellooppmmeenntt MMooddeell
 Suitable for all types of projects - "this is how it works
anyhow."
 Pros:
·Provides both process visibility and
concurrent phases
 Cons:
·Complicated to keep track of - requires
tools.
November 5, 2014 30

31. TThhee CCoonnccuurrrreenntt DDeevveellooppmmeenntt MMooddeell
November 5, 2014 31

32. Unified Software
Development Process
Developed by the team that created UML
Embodies best practice in system
development
Adopts an iterative approach with four
main phases
Different tasks are captured in a series of
workflows
November 5, 2014 32

33. Best Practice
Iterative and incremental development
Component-based development
Requirements-driven development
Configurability
Architecture-centrism
Visual modelling techniques
November 5, 2014 33

34. Four Phases
Inception
Elaboration
Construction
Transition
November 5, 2014 34

35. Phases, Workflows
and Iterations
Within each phase activities are grouped
into workflows
The balance of effort spent in each
workflow varies from phase to phase
Within phases there may be more than
one iteration
November 5, 2014 35

36. Inception Elaboration Construction Transition
1 2 3 4 5 6 7 8
Size of square
relative to time
spent on
workflowh
Project
Phases
November 5, 2014 36
Iterations within
Requirements each phase
Analysis
Design
Implementation
Test
Workflows

37. Difference from
Waterfall Life Cycle
 In a waterfall life cycle project the phases and
the workflows are linked together
 In the Requirements phase, only Requirements
workflow activities are carried out
 All Requirements activity should be completed
before work starts on Analysis
 In an iterative life cycle project it is recognised
that some Requirements work will be
happening alongside Analysis work
November 5, 2014 37

38. Requirements
Analysis
Design
Implementation
Test
Requirements
Analysis
Design
Implementation
Test
November 5, 2014 38

39. Major Activities of the
Development Process
Activity Techniques Key Deliverables
Requirements
Capture and
Modelling
Requirements
Elicitation
Use Case
Modelling
Prototyping
Use Case Model
Requirements List
Prototypes
Glossary
November 5, 2014 39

40. Major Activities of the
Development Process
Activity Techniques Key Deliverables
Requirements
Analysis
Collaboration
Diagrams
Class and Object
Models
Analysis
Modelling
Analysis Models
November 5, 2014 40

41. Major Activities of the
Development Process
Activity Techniques Key Deliverables
System
Design
Deployment
Modelling
Component
Modelling
Package
Modelling
Architectural
Modelling
Overview Design
and
Implementation
Architecture
November 5, 2014 41

42. Major Activities of the
Development Process
Activity Techniques Key Deliverables
Class Design Class and Object
Modelling
Interaction
Modelling
State Modelling
Design Patterns
Design Models
November 5, 2014 42

43. Major Activities of the
Development Process
Activity Techniques Key Deliverables
User
Interface
Design
Class and Object
Modelling
Interaction Modelling
State Modelling
Package Modelling
Prototyping
Design Patterns
Design Models
with Interface
Specification
November 5, 2014 43

44. Major Activities of the
Development Process
Activity Techniques Key Deliverables
Data
Management
Design
Class and Object
Modelling
Interaction
Modelling
State Modelling
Package
Modelling
Design Patterns
Design Models
with Database
Specification
November 5, 2014 44

45. Major Activities of the
Development Process
Activity Techniques Key Deliverables
Construction Programming
Component Re-use
Database DDL
Programming
Idioms
Constructed
System
Documentation
November 5, 2014 45