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Software Processes

©Ian Sommerville 2004

Software Engineering, 7th edition. Chapter 4

Slide 1
Objectives
To introduce software process models
To describe three generic process models and
when they may be used
To desc...
Topics covered
Software process models
Process iteration
Process activities
The Rational Unified Process
Computer-aided so...
The software process
A structured set of activities required to develop a
software system
•
•
•
•

Specification;
Design;
...
Generic software process models
The waterfall model
•

Separate and distinct phases of specification and
development.

Evo...
Rquir
esoftw
ement
definit
SImpl
yand
stem
tion
Inte
rOp
am
tio
sys
aio
t
Waterfall model

©Ian Sommerville 2004

Software...
Waterfall model phases
Requirements analysis and definition
System and software design
Implementation and unit testing
Int...
Waterfall model problems
Inflexible partitioning of the project into distinct stages
makes it difficult to respond to chan...
Evolutionary development
Exploratory development
•

Objective is to work with customers and to evolve
a final system from ...
Conc
entr
acti
vitie
In
Spec
tion
vr
e
Int
m
te
Outlin
Devr
vlida
elop
e
descrip
Fi
Vv
a e
tion
Evolutionary development

...
Evolutionary development
Problems
•
•
•

Lack of process visibility;
Systems are often poorly structured;
Special skills (...
Component-based software engineering
Based on systematic reuse where systems are
integrated from existing components or CO...
Reuse-oriented development

Requirem
Compo
Requ
Sva
yste
specifica
analysi
modi
with
Dev
S
y
ands
ratio
©Ian Sommerville 2...
Process iteration
System requirements ALWAYS evolve in the
course of a project so process iteration where
earlier stages a...
Incremental delivery
Rather than deliver the system as a single delivery, the
development and delivery is broken down into...
Assign
Desi
Defineli
requireo
arto
chit
eV
Develop
Vincr y
alidas
teeme
Integ
resy
a aF
t te
incrstem
ement
incr
ement
S
y...
Incremental development advantages
Customer value can be delivered with each
increment so system functionality is availabl...
Extreme programming
An approach to development based on the
development and delivery of very small
increments of functiona...
Spiral development
Process is represented as a spiral rather than
as a sequence of activities with backtracking.
Each loop...
DeterEvs,
mineiden
v Risk
e ysis
obj
alua
te
ti
v
e
alternar r
tis and a
v s,Risk
e anal
,e
eso
constrOp
aintsPr
Risk
anal...
Spiral model sectors
Objective setting
•

Specific objectives for the phase are identified.

Risk assessment and reduction...
Process activities
Software specification
Software design and implementation
Software validation
Software evolution

©Ian ...
Software specification
The process of establishing what services are
required and the constraints on the system’s
operatio...
Rquir
e Rqu
emen
Fasibili
easibil
elicita
stud Rq
ypor e
anal
ysis
e va
em
spec
em
F SUse
e mode
rt ystem
requ
Rq
e
em
do
...
Software design and implementation
The process of converting the system
specification into an executable system.
Software ...
Design process activities
Architectural design
Abstract specification
Interface design
Component design
Data structure des...
Rquirstru
eAbstr A
ements
specific
tion des
Desig
vitie
Da
ta
Ar InterA
chitectur
aleInterd
actdesi
face
Com
designesti
sp...
Structured methods
Systematic approaches to developing a
software design.
The design is usually documented as a set of
gra...
Programming and debugging
Translating a design into a program and
removing errors from that program.
Programming is a pers...
DRpa
esig
Locapr
teepair
erRem
err o
or g
err err
or ora
r
The debugging process

©Ian Sommerville 2004

Software Engineer...
Software validation
Verification and validation (V & V) is intended
to show that a system conforms to its
specification an...
Sste
yA
Comp
test
te
testin
The testing process

©Ian Sommerville 2004

Software Engineering, 7th edition. Chapter 4

Slid...
Testing stages
Component or unit testing
•
•

Individual components are tested independently;
Components may be functions ...
Testing phases

RquirrDet
eAccepta
ementsun
SySades
ySytion
stem
stem
specifica
tionstem
specific
tion pl
desig
SubM
integ...
Software evolution
Software is inherently flexible and can change.
As requirements change through changing
business circum...
Define
Asse
Pro
M
require
syste
cha
sy
Exist
N
syste
sy
System evolution

©Ian Sommerville 2004

Software Engineering, 7th...
The Rational Unified Process
A modern process model derived from the
work on the UML and associated process.
Normally desc...
RUP phase model

Phase
Inceptio
Elabor
Con
T
ra
©Ian Sommerville 2004

Software Engineering, 7th edition. Chapter 4

Slide...
RUP phases
Inception
•

Establish the business case for the system.

Elaboration
•

Develop an understanding of the proble...
RUP good practice
Develop software iteratively
Manage requirements
Use component-based architectures
Visually model softwa...
Static workflows
Workflow

Description

Business modelling

The business processes are modelled using business use cases.
...
Computer-aided software engineering
Computer-aided software engineering (CASE) is
software to support software development...
Case technology
Case technology has led to significant
improvements in the software process.
However, these are not the or...
CASE classification
Classification helps us understand the different types
of CASE tools and their support for process act...
Functional tool classification
Tool type

Examples

Planning tools

PERT tools, estimation tools, spreadsheets

Editing to...
Re-eng
ineering
Tsting too
e tools
Debugg
ing analy
Prog su
ram
Language
tools
Method
t tools
Prototypin
Configura
managem...
CASE integration
Tools
•

Support individual process tasks such as design
consistency checking, text editing, etc.

Workbe...
C SE
A
techn
gEn
yvir
Wed
oInteg
kbenc
r Pr
Tcompa
oolsonm
Filean
r en
aoce
t vir
Editorsed
Compil
aaen
tPr onm
ors
vir
on...
Key points
Software processes are the activities involved in
producing and evolving a software system.
Software process mo...
Key points
Requirements engineering is the process of
developing a software specification.
Design and implementation proce...
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  1. 1. Software Processes ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 1
  2. 2. Objectives To introduce software process models To describe three generic process models and when they may be used To describe outline process models for requirements engineering, software development, testing and evolution To explain the Rational Unified Process model To introduce CASE technology to support software process activities ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 2
  3. 3. Topics covered Software process models Process iteration Process activities The Rational Unified Process Computer-aided software engineering ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 3
  4. 4. The software process A structured set of activities required to develop a software system • • • • Specification; Design; Validation; Evolution. A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 4
  5. 5. Generic software process models The waterfall model • Separate and distinct phases of specification and development. Evolutionary development • Specification, development and validation are interleaved. Component-based software engineering • The system is assembled from existing components. There are many variants of these models e.g. formal development where a waterfall-like process is used but the specification is a formal specification that is refined through several stages to an implementable design. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 5
  6. 6. Rquir esoftw ement definit SImpl yand stem tion Inte rOp am tio sys aio t Waterfall model ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 6
  7. 7. Waterfall model phases Requirements analysis and definition System and software design Implementation and unit testing Integration and system testing Operation and maintenance The main drawback of the waterfall model is the difficulty of accommodating change after the process is underway. One phase has to be complete before moving onto the next phase. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 7
  8. 8. Waterfall model problems Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements. Therefore, this model is only appropriate when the requirements are well-understood and changes will be fairly limited during the design process. Few business systems have stable requirements. The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 8
  9. 9. Evolutionary development Exploratory development • Objective is to work with customers and to evolve a final system from an initial outline specification. Should start with well-understood requirements and add new features as proposed by the customer. Throw-away prototyping • Objective is to understand the system requirements. Should start with poorly understood requirements to clarify what is really needed. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 9
  10. 10. Conc entr acti vitie In Spec tion vr e Int m te Outlin Devr vlida elop e descrip Fi Vv a e tion Evolutionary development ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 10
  11. 11. Evolutionary development Problems • • • Lack of process visibility; Systems are often poorly structured; Special skills (e.g. in languages for rapid prototyping) may be required. Applicability • • • For small or medium-size interactive systems; For parts of large systems (e.g. the user interface); For short-lifetime systems. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 11
  12. 12. Component-based software engineering Based on systematic reuse where systems are integrated from existing components or COTS (Commercial-off-the-shelf) systems. Process stages • • • • Component analysis; Requirements modification; System design with reuse; Development and integration. This approach is becoming increasingly used as component standards have emerged. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 12
  13. 13. Reuse-oriented development Requirem Compo Requ Sva yste specifica analysi modi with Dev S y ands ratio ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 13
  14. 14. Process iteration System requirements ALWAYS evolve in the course of a project so process iteration where earlier stages are reworked is always part of the process for large systems. Iteration can be applied to any of the generic process models. Two (related) approaches • • Incremental delivery; Spiral development. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 14
  15. 15. Incremental delivery Rather than deliver the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality. User requirements are prioritised and the highest priority requirements are included in early increments. Once the development of an increment is started, the requirements are frozen though requirements for later increments can continue to evolve. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 15
  16. 16. Assign Desi Defineli requireo arto chit eV Develop Vincr y alidas teeme Integ resy a aF t te incrstem ement incr ement S y Incremental development ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 16
  17. 17. Incremental development advantages Customer value can be delivered with each increment so system functionality is available earlier. Early increments act as a prototype to help elicit requirements for later increments. Lower risk of overall project failure. The highest priority system services tend to receive the most testing. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 17
  18. 18. Extreme programming An approach to development based on the development and delivery of very small increments of functionality. Relies on constant code improvement, user involvement in the development team and pairwise programming. Covered in Chapter 17 ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 18
  19. 19. Spiral development Process is represented as a spiral rather than as a sequence of activities with backtracking. Each loop in the spiral represents a phase in the process. No fixed phases such as specification or design - loops in the spiral are chosen depending on what is required. Risks are explicitly assessed and resolved throughout the process. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 19
  20. 20. DeterEvs, mineiden v Risk e ysis obj alua te ti v e alternar r tis and a v s,Risk e anal ,e eso constrOp aintsPr Risk anal ysis aanal ysis otot tio oto yp Prpr ototy Risk Pr, ks otoanal Rysisbe EaS/W EWmo VI type Rquir e Conce ements Sim tion ,Cod Life-cy cleula pla Oper trion Pr odu eInteg emen quir De desi Rlida etest emen Dequir viondes ephase lopme v testp a retes tion planlop Uni Integl rServic aDesig t V&V ion andtv v Plan a,erif xt Acce ne De xt-l v e odu Spiral model of the software process ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 20
  21. 21. Spiral model sectors Objective setting • Specific objectives for the phase are identified. Risk assessment and reduction • Risks are assessed and activities put in place to reduce the key risks. Development and validation • A development model for the system is chosen which can be any of the generic models. Planning • The project is reviewed and the next phase of the spiral is planned. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 21
  22. 22. Process activities Software specification Software design and implementation Software validation Software evolution ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 22
  23. 23. Software specification The process of establishing what services are required and the constraints on the system’s operation and development. Requirements engineering process • • • • Feasibility study; Requirements elicitation and analysis; Requirements specification; Requirements validation. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 23
  24. 24. Rquir e Rqu emen Fasibili easibil elicita stud Rq ypor e anal ysis e va em spec em F SUse e mode rt ystem requ Rq e em do The requirements engineering process ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 24
  25. 25. Software design and implementation The process of converting the system specification into an executable system. Software design • Design a software structure that realises the specification; Implementation • Translate this structure into an executable program; The activities of design and implementation are closely related and may be inter-leaved. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 25
  26. 26. Design process activities Architectural design Abstract specification Interface design Component design Data structure design Algorithm design ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 26
  27. 27. Rquirstru eAbstr A ements specific tion des Desig vitie Da ta Ar InterA chitectur aleInterd actdesi face Com designesti specific tionstru design ta Sspecific ystemDa Softw p artion face Com e artionspe chitectur e specif spec tion tio Desig oduc The software design process ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 27
  28. 28. Structured methods Systematic approaches to developing a software design. The design is usually documented as a set of graphical models. Possible models • • • • • Object model; Sequence model; State transition model; Structural model; Data-flow model. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 28
  29. 29. Programming and debugging Translating a design into a program and removing errors from that program. Programming is a personal activity - there is no generic programming process. Programmers carry out some program testing to discover faults in the program and remove these faults in the debugging process. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 29
  30. 30. DRpa esig Locapr teepair erRem err o or g err err or ora r The debugging process ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 30
  31. 31. Software validation Verification and validation (V & V) is intended to show that a system conforms to its specification and meets the requirements of the system customer. Involves checking and review processes and system testing. System testing involves executing the system with test cases that are derived from the specification of the real data to be processed by the system. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 31
  32. 32. Sste yA Comp test te testin The testing process ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 32
  33. 33. Testing stages Component or unit testing • • Individual components are tested independently; Components may be functions or objects or coherent groupings of these entities. System testing • Testing of the system as a whole. Testing of emergent properties is particularly important. Acceptance testing • Testing with customer data to check that the system meets the customer’s needs. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 33
  34. 34. Testing phases RquirrDet eAccepta ementsun SySades ySytion stem stem specifica tionstem specific tion pl desig SubM integ t rinteg ayion tSstem ionan testinteg plan testion test Accept Sub Service testinte rr aa t t ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 34
  35. 35. Software evolution Software is inherently flexible and can change. As requirements change through changing business circumstances, the software that supports the business must also evolve and change. Although there has been a demarcation between development and evolution (maintenance) this is increasingly irrelevant as fewer and fewer systems are completely new. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 35
  36. 36. Define Asse Pro M require syste cha sy Exist N syste sy System evolution ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 36
  37. 37. The Rational Unified Process A modern process model derived from the work on the UML and associated process. Normally described from 3 perspectives • • • A dynamic perspective that shows phases over time; A static perspective that shows process activities; A practive perspective that suggests good practice. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 37
  38. 38. RUP phase model Phase Inceptio Elabor Con T ra ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 38
  39. 39. RUP phases Inception • Establish the business case for the system. Elaboration • Develop an understanding of the problem domain and the system architecture. Construction • System design, programming and testing. Transition • Deploy the system in its operating environment. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 39
  40. 40. RUP good practice Develop software iteratively Manage requirements Use component-based architectures Visually model software Verify software quality Control changes to software ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 40
  41. 41. Static workflows Workflow Description Business modelling The business processes are modelled using business use cases. Requirements Actors who interact with the system are identified and use cases are developed to model the system requirements. Analysis and design A design model is created and documented using architectural models, component models, object models and sequence models. Implementation The components in the system are implemented and structured into implementation sub-systems. Automatic code generation from design models helps accelerate this process. Test Testing is an iterative process that is carried out in conjunction with implementation. System testing follows the completion of the implementation. Deployment A product release is created, distributed to users and installed in their workplace. Configuration and change management This supporting workflow managed changes to the system (see Chapter 29). Project management This supporting workflow manages the system development (see Chapter 5). Environment This workflow is concerned with making appropriate software tools available to the software development team. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 41
  42. 42. Computer-aided software engineering Computer-aided software engineering (CASE) is software to support software development and evolution processes. Activity automation • • • • • Graphical editors for system model development; Data dictionary to manage design entities; Graphical UI builder for user interface construction; Debuggers to support program fault finding; Automated translators to generate new versions of a program. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 42
  43. 43. Case technology Case technology has led to significant improvements in the software process. However, these are not the order of magnitude improvements that were once predicted • • Software engineering requires creative thought this is not readily automated; Software engineering is a team activity and, for large projects, much time is spent in team interactions. CASE technology does not really support these. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 43
  44. 44. CASE classification Classification helps us understand the different types of CASE tools and their support for process activities. Functional perspective • Tools are classified according to their specific function. Process perspective • Tools are classified according to process activities that are supported. Integration perspective • Tools are classified according to their organisation into integrated units. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 44
  45. 45. Functional tool classification Tool type Examples Planning tools PERT tools, estimation tools, spreadsheets Editing tools Text editors, diagram editors, word processors Change management tools Requirements traceability tools, change control systems Configuration management tools Version management systems, system building tools Prototyping tools Very high-level languages, user interface generators Method-support tools Design editors, data dictionaries, code generators Language-processing tools Compilers, interpreters Program analysis tools Cross reference generators, static analysers, dynamic analysers Testing tools Test data generators, file comparators Debugging tools Interactive debugging systems Documentation tools Page layout programs, image editors Re-engineering tools Cross-reference systems, program re-structuring systems ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 45
  46. 46. Re-eng ineering Tsting too e tools Debugg ing analy Prog su ram Language tools Method t tools Prototypin Configura managem Change to m Documen Editingrifi Planning Specific Design Imple V elida and a Activity-based tool classification ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 46
  47. 47. CASE integration Tools • Support individual process tasks such as design consistency checking, text editing, etc. Workbenches • Support a process phase such as specification or design, Normally include a number of integrated tools. Environments • Support all or a substantial part of an entire software process. Normally include several integrated workbenches. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 47
  48. 48. C SE A techn gEn yvir Wed oInteg kbenc r Pr Tcompa oolsonm Filean r en aoce t vir Editorsed Compil aaen tPr onm ors vir onm Anal ysisLan oal-pu gmm rGene Tstin egedesign Multi-m wrororor o Single kbenche www kbenc kben kbe Tools, workbenches, environments ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 48
  49. 49. Key points Software processes are the activities involved in producing and evolving a software system. Software process models are abstract representations of these processes. General activities are specification, design and implementation, validation and evolution. Generic process models describe the organisation of software processes. Examples include the waterfall model, evolutionary development and componentbased software engineering. Iterative process models describe the software process as a cycle of activities. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 49
  50. 50. Key points Requirements engineering is the process of developing a software specification. Design and implementation processes transform the specification to an executable program. Validation involves checking that the system meets to its specification and user needs. Evolution is concerned with modifying the system after it is in use. The Rational Unified Process is a generic process model that separates activities from phases. CASE technology supports software process activities. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 4 Slide 50
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