Transcript Software Processes - University of Nebraska Omaha

Software Process Models
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 1
Objectives
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

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
To introduce software process models
To describe three generic process models
and when they may be used
To 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
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 2
Topics covered


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
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Software process models
Process iteration
Process activities
The Rational Unified Process
Computer-aided software engineering
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 3
The software process

A structured set of activities required to develop a
software system
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•
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 4
Generic software process models
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The waterfall model
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Evolutionary development
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Specification, development and validation are
interleaved.
Component-based software engineering
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Separate and distinct phases of specification and
development.
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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 5
Waterfall model
Requirements
definition
System and
software design
Implementation
and unit testing
Integration and
system testing
Operation and
maintenance
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 6
Waterfall model phases
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 7
Waterfall model problems
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 8
Evolutionary development
Concurrent
activities
Initial
version
Specification
Outline
description
Development
Intermedia te
versions
Validation
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Final
version
Slide 9
Evolutionary development
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Exploratory development
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 10
Evolutionary development
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Problems
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Lack of process visibility;
Systems are often poorly structured;
Special skills (e.g. in languages for rapid
prototyping) may be required.
Applicability
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For small or medium-size interactive systems;
For parts of large systems (e.g. the user
interface);
For short-lifetime systems.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 11
Component-based software
engineering
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Based on systematic reuse where systems
are integrated from existing components or
COTS (Commercial-off-the-shelf) systems.
Process stages
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Component analysis;
Requirements modification;
System design with reuse;
Development and integration.
This approach is becoming increasingly
used as component standards have
emerged.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 12
Reuse-oriented development
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 13
Topics covered

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Software process models
Process iteration
Process activities
The Rational Unified Process
Computer-aided software engineering
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 14
Process iteration
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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
•
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Incremental delivery;
Spiral development.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 15
Incremental delivery
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 16
Incremental development
Define outline
requirements
Develop system
increment
Assign requirements
to increments
Validate
increment
Design system
architecture
Integrate
increment
Validate
system
Final
system
System incomplete
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 17
Incremental development
advantages
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 18
Incremental development
disadvantages
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Increments should be relatively small and
still deliver some functionality
Might be difficult to map customer
requirements into increments
High level requirements may not be
sufficient to define system architecture
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 19
Agile software development
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Lightweight process for incremental delivery
Manifesto:
We are uncovering better ways of developing software by doing it
and helping others do it. Through this work we have come to value:
Individuals and interactions over processes and tools
Working software over comprehensive documentation
Customer collaboration over contract negotiation
Responding to change over following a plan
That is, while there is value in the items on the right,
we value the items on the left more.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 20
Extreme programming
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An agile method
“Extreme” because:
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Extreme customer involvement
• On-site customer
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Extreme iterative development
• Incremental planning, small releases, continuous integration,
sustainable pace
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Extreme teamwork
• Pair programming, collective ownership
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Extreme defect prevention
• Simple design, test-first development, refactoring
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 21
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 22
Extreme programming practices 1
Incremental planning
Requirements are recorded on Story Cards and the Stories to be
included in a release are determined by the time available and
their relative priority. The developers break these Stories into
development ‘Tasks’.
Small Releases
The minimal useful set of functionality that provides business
value is developed first. Releases of the system are frequent and
incrementally add functionality to the first release.
Simple Design
Enough design is carried out to meet the current requirements
and no more.
Test first development
An automated unit test framework is used to write tests for a new
piece of functionality before that functionality itself is
implemented.
Refactoring
All developers are expected to refactor the code continuously as
soon as possible code improvements are found. This keeps the
code simple and maintainable.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 23
Extreme programming practices 2
Pair Programming
Developers work in pairs, checking each other’s work and
providing the support to always do a good job.
Collective Ownership
The pairs of developers work on all areas of the system, so that
no islands of expertise develop and all the developers own all the
code. Anyone can change anything.
Continuous Integration As soon as work on a task is complete it is integrated into the
whole system. After any such integration, all the unit tests in the
system must pass.
Sustainable pace
Large amounts of over-time are not considered acceptable as the
net effect is often to reduce code quality and medium term
productivity
On-site Customer
A representative of the end-user of the system (the Customer)
should be available full time for the use of the XP team. In an
extreme programming process, the customer is a member of the
development team and is responsible for bringing system
requirements to the team for implementation.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 24
Spiral development
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 26
Spiral model of the software process
Deter mine objecti ves,
alterna tives and
constr aints
Evalua te alterna tives,
identify , resolv e risks
Risk
analysis
Risk
anal ysis
Risk
anal ysis
REVIEW
Requir ements plan
Life-cycle plan
Plan ne xt phase
Prototype 2
Risk
anal ysis Prototype 1
Simula tions , models , benchmar ks
Concept of
Oper ation
S/W
requir ements
Development
plan
Requir ement
validation
Integ ration
and test plan
Design
V&V
Service
Modified from Sommerville’s originals
Oper ational
pr otoype
Prototype 3
Product
design
Detailed
design
Code
Unit test
Acceptance
test
Integ ration
test
Develop , verify
next-le vel pr oduct
Software Engineering, 7th edition. Chapter 4
Slide 27
Spiral model sectors
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Objective setting
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Risk assessment and reduction
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Risks are assessed and activities put in place to
reduce the key risks.
Development and validation
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Specific objectives for the phase are identified.
A development model for the system is chosen
which can be any of the generic models.
Planning
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The project is reviewed and the next phase of the
spiral is planned.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 28
Topics covered





Software process models
Process iteration
Process activities
The Rational Unified Process
Computer-aided software engineering
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 29
Process activities
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Software specification
Software design and implementation
Software validation
Software evolution
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 30
Software specification
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The process of establishing what services
are required and the constraints on the
system’s operation and development.
Requirements engineering process
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Feasibility study;
Requirements elicitation and analysis;
Requirements specification;
Requirements validation.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 31
The requirements engineering process
Feasibility
study
Requirements
elicitation and
analysis
Requirements
specification
Requirements
validation
Feasibility
repor t
System
models
User and system
requirements
Requirements
document
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 32
Software design and implementation
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The process of converting the system
specification into an executable system.
Software design
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Implementation
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Design a software structure that realises the
specification;
Translate this structure into an executable
program;
The activities of design and implementation
are closely related and may be inter-leaved.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 33
Design process activities
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Architectural design
Abstract specification
Interface design
Component design
Data structure design
Algorithm design
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 34
The software design process
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 35
Components of a design method
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A set of system models
Rules that apply to these models
Guidelines for ‘good’ design
Design process model
Format of design document
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 36
Structured methods
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Systematic approaches to developing a
software design.
The design is usually documented as a set
of graphical models.
Possible models
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Object model;
Sequence model;
State transition model;
Structural model;
Data-flow model.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 37
Programming and debugging
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 38
The debugging process
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 39
Software validation
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 40
The testing process
Component
testing
Modified from Sommerville’s originals
System
testing
Software Engineering, 7th edition. Chapter 4
Acceptance
testing
Slide 41
Testing stages
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Component or unit testing
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System testing
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Individual components are tested
independently;
Components may be functions or objects or
coherent groupings of these entities.
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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 42
Testing phases
Requirements
specification
System
specification
System
integration
test plan
Acceptance
test plan
Service
System
design
Acceptance
test
Modified from Sommerville’s originals
Detailed
design
Sub-system
integ ration
test plan
System
integ ration test
Module and
unit code
and test
Sub-system
integ ration test
Software Engineering, 7th edition. Chapter 4
Slide 43
Software evolution
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 44
System evolution
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 45
Topics covered
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Software process models
Process iteration
Process activities
The Rational Unified Process
Computer-aided software engineering
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 46
The Rational Unified Process
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A modern process model derived from the
work on the UML and associated process.
Normally described from 3 perspectives
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A dynamic perspective that shows phases over
time;
A static perspective that shows process
activities;
A practice perspective that suggests good
practice.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 47
RUP phase model
P has e i terati on
Incepti on
Elaborati on
Modified from Sommerville’s originals
Cons tructi on
Software Engineering, 7th edition. Chapter 4
Transi tion
Slide 48
RUP phases
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Inception
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Elaboration
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Develop an understanding of the problem
domain and the system architecture.
Construction
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Establish the business case for the system.
System design, programming and testing.
Transition
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Deploy the system in its operating environment.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 49
RUP good practice
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Develop software iteratively
Manage requirements
Use component-based architectures
Visually model software
Verify software quality
Control changes to software
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 50
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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 51
Dynamic Phases and
Static Workflows
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 52
Topics covered




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Software process models
Process iteration
Process activities
The Rational Unified Process
Computer-aided software engineering
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 53
Computer-aided software
engineering
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Computer-aided software engineering (CASE) is
software to support software development and
evolution processes.
Activity automation
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•
•
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 54
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
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•
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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 55
CASE classification
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Classification helps us understand the different
types of CASE tools and their support for process
activities.
Functional perspective
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Process perspective
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Tools are classified according to their specific
function.
Tools are classified according to process activities
that are supported.
Integration perspective
•
Tools are classified according to their organisation
into integrated units.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 56
Functional tool classification
Tool type
Examples
Planning tools
PERT tools, estimation tools, spreadsheets
Editing tools
Text editors, diagram editors, word processors
Change ma nagement tools
Requirements traceability tools, change control systems
Configuration management tools
Version management systems, system b uilding 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 comp arators
Debugging tools
Interactive debugging systems
Documentation tools
Page layout programs , ima ge editors
Re-engineering tools
Cross-reference systems , program re-structuring systems
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 57
Activity-based tool classification
Re-eng in eerin g to ols
Tes tin g to ols
Deb ug g in g too ls
Prog ram an aly sis to ols
Lang u ag e-p ro ces sin g
to ols
Meth o d s up po r t too ls
Prototy p ing to ols
Con fig uration
man ag emen t to ols
Chang e man ag emen t too ls
Documen tatio n too ls
Editing too ls
Plan ning to o ls
Specificatio n
Modified from Sommerville’s originals
Design
Implemen tatio n
Verification
an d
Validatio n
Software Engineering, 7th edition. Chapter 4
Slide 58
CASE integration
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Tools
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Workbenches
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Support individual process tasks such as design
consistency checking, text editing, etc.
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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 59
Tools, workbenches, environments
CASE
technology
Workbenches
Tools
Editors
Compilers
File
comparators
Analysis and
design
Multi-method
workbenches
Modified from Sommerville’s originals
Integrated
environments
Programming
Single-method
workbenches
Environments
Process-centred
environments
Testing
General-purpose
workbenches
Language-specific
workbenches
Software Engineering, 7th edition. Chapter 4
Slide 60
Key points
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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
component-based software engineering.
Iterative process models describe the software
process as a cycle of activities.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 62
Key points
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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.
Modified from Sommerville’s originals
Software Engineering, 7th edition. Chapter 4
Slide 63