Transcript Software Engineering Chapter 4 Software processes

Software Engineering
Chapter 4
Software processes
Ku-Yaw Chang
[email protected]
Assistant Professor
Department of Computer Science and Information Engineering
Da-Yeh University
Objectives
Understand the concept of software process and
software process model
Understand three generic software process models and
when they might be used
Understand, in outline, the activities involved in software
requirements engineering, software development, testing
and evolution
Understand how the Rational Unified Process integrates
good software process practice to create a modern,
generic process model
Have been introduced to CASE technology that is used
to support software process activities
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Preamble
A software process
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
A set of activities that leads to the production of a
software product
No ideal process
Many organizations have developed their own approach to
software development
Fundamental activities to all software processes
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Specification
Design and implementation
Validation
Evolution
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Contents
4.1 Software process models
4.2 Process iteration
4.3 Process activities
4.4 The Rational Unified Process
4.5 Computer-Aided Software Engineering
4.6 Exercises
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4.1 Software process models
A software process model
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An abstract representation of a software process
Represent a process from a particular perspective
General process models ( sometimes called
process paradigms)
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The waterfall model
Evolutionary (Iterative) development
Component-based software engineering
The above models are not mutual exclusive

Often be used together
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4.1.1 The waterfall model
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Waterfall model phases
Requirements analysis and definition
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Service, constraints and goals
Consultation with system users
System and software design
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System design
Partition the requirements to either hardware or software systems
Establish an overall system architecture
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Software design
Identify and describe the fundamental software abstractions and
their relationships
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Waterfall model phases
Implementation and unit testing
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Software design is realized
A set of programs or program units
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Unit testing
Verify that each unit meets its specification
Integration and system testing
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Integrate individual program units or programs
Be tested as a complete system
Operation and maintenance
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Install the system and put it into practical use
Maintenance
Correct errors
Improve the implementation
Enhance services
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The waterfall model
Advantages
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The documentation is produced at each phase
It fits with other engineering process models
Particularly when the software project is part of a larger
system engineering project.
Disadvantages
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Inflexible partitioning of the project into distinct stages
Commitments must be made at an early stage
Difficult to respond to changing customer requirements
Only appropriate when the requirements are well-understood
and changes will be fairly limited during the design process.
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Few business systems have stable requirements.
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4.1.2 Evolutionary development
Based on the idea of
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Developing an initial implementation
Exposing this to user commitment
Refining it through many versions
Specification, development and validation
activities are interleaved rather than separate
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With rapid feedback across activities
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Evolutionary development
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Two fundamental types
Exploratory development
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Work with customers and to evolve a final system
from an initial outline specification
Start with well-understood requirements and add new
features as proposed by the customer
Throwaway prototyping
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Understand the system requirements
Start with poorly understood requirements to clarify
what is really needed
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Evolutionary development
Often more effective than the waterfall approach
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In producing systems that meet the immediate needs
of customers
Advantage
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The specification can be developed incrementally
Disadvantages
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The process is not visible
Not cost-effective to produce documents that reflect every
version of the system
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Systems are often poorly structured
Continual change tends to corrupt the software structure
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Evolutionary development
Applicability
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For small or medium-size systems (up to 500,000
lines of code)
For parts of large systems (e.g. the user interface)
A mixed process incorporating the waterfall and evolutionary
models
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A throwaway prototyping to resolve uncertainties in the system
specification
Implement the system in a more structural approach
The user interface could be developed using an exploratory
approach
For short-lifetime systems
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4.1.3 Component-based
software engineering
Software reuse
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The majority of software projects
Essential for rapid system development
CBSE
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Based on systematic reuse where systems are
integrated from existing components or COTS
(Commercial-off-the-shelf) systems
Becoming increasingly used as component standards
have emerged
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Component-based
software engineering
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CBSE stages
System specification
Component analysis
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A search is made for components
Usually no exact match
Requirements modification
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Analyze requirements using information about components that have
been discovered
System design and reuse
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Take into account the components that are reuse
Reorganize the framework of the system
Some new software may be designed reusable components are not
available
Development and integration
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Develop software that cannot be externally procured
Integrate newly developed software and COTS systems
System validation
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Component-based
software engineering
Advantages
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Reduce the amount of software to be developed
Costs and risk
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Lead to faster delivery of the software
Disadvantages
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Requirements compromises are inevitable
Some control over the system evolution is lost
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Contents
4.1 Software process models
4.2 Process iteration
4.3 Process activities
4.4 The Rational Unified Process
4.5 Computer-Aided Software Engineering
4.6 Exercises
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Process iteration
Change is inevitable in large software projects
The essence of iterative processes
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The specification is developed in conjunction with the
software
Conflict with the procurement model of many
organizations
The complete system specification is part of the system
development contract
Two process models to support process iteration
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Incremental delivery
Spiral development
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4.2.1 Incremental delivery
Waterfall model
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Separation of design and implementation leads to
well-documented systems that are amenable to
change
Evolutionary development
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May be poorly structured and difficult to understand
and maintain
Incremental delivery
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An in-between approach that combines the
advantages of the above models
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Incremental delivery
Customers outline the services
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Identify which are most/least important
Define a number of delivery increments
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Each increment provide a sub-set of the system
functionality
Develop an increment
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Requirements are defined in detail
Further requirements analysis for later increments
can take place
Put an increment into service
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New increments are integrated with existing
increments
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Incremental delivery
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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
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Incremental development
Problems
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Difficult to map requirements onto increments of the
right size
Relatively small – no more than 20,000 lines of code
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Hard to identify facilities that are needed by all
increments
Extreme programming
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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.
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4.2.2 Spiral development
The software process is represented as a
spiral
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Each loop represents a phase
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Spiral model
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Contents
4.1 Software process models
4.2 Process iteration
4.3 Process activities
4.4 The Rational Unified Process
4.5 Computer-Aided Software Engineering
4.6 Exercises
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Process Activities
Basic process activities
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Specification, development, validation, and
evolution
Organized in sequence in the waterfall model
Interleaved in evolutionary development
No right or wrong way to organize these
activities
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Depend on the type of software, people and
organizational structures involved
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4.3.1 Software specification
Also called requirements engineering (RE)
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The process of
Understanding and defining required services
Identifying constraints on operation and development
Four main phases in the RE process
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Feasibility study
Requirements elicitation and analysis
Requirements specification
Requirements validation
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The requirements engineering process
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4.3.2 Software design and
implementation
Software development
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The process of converting a system specification into
an executable system
Design process
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Developing several models of the system at different
levels of abstraction
Stages are sequential
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A specification for the next stage is the output of each
design activity
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A general model of
the design process
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Structured methods
Structured methods
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Be invented in 1970s to support function-oriented
design
Produce graphical models of the system
Automatically generating code from these models
Various competing methods to support objectoriented design were unified in the 1990s
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Unified Modeling Language (UML)
Current official version : 2.1.1 (2007/04)
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Unified design process
Rational Unified Process (RUP)
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Structured methods
Support part or all of the following models
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An object model
Object classes and dependencies
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A sequence model
Objects interaction during execution
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A state transition model
System states and triggers for the transitions
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A structural model
System components and their aggregations
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A data flow model
Focus on the data transformations
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The debugging process
Testing
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Establish the existing of defects
Debugging
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Locating and correcting these defects
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4.3.3 Software validation
Verification and Validation ( V & V )
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Verification
a system conforms to its specification
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Validation
the system meets the expectations of the customer
Systems should not be tested as a single,
monolithic unit.
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A three-stage testing process
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The testing process
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Stages in the testing process
Component (or unit) testing
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Individual components are tested independently;
Components may be functions or objects or coherent
groupings of these entities.
System testing
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Testing of the system as a whole. Testing of emergent
properties is particularly important.
Acceptance testing
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Testing with customer data to check that the system
meets the customer’s needs.
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4.3.3 Software validation
Component development and testing are
interleaved
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An economically sensible approach
Programmers make up their own test data and test the code
as it is developed.
Alpha testing
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Sometimes called acceptance testing
The system developer and the client agree that the
delivered system is an acceptable implementation
Beta testing
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Delivering a system to a number of potential
customers
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Testing phases
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System evolution
It makes more sense to see development and
maintenance as a continuum.
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Contents
4.1 Software process models
4.2 Process iteration
4.3 Process activities
4.4 The Rational Unified Process
4.5 Computer-Aided Software Engineering
4.6 Exercises
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Rational Unified Process
Rational Unified Process (RUP)
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A modern process model that derived from work on
the UML and associated process
OMG’s Unified Modeling Language
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Rational Unified Process
Be described from three perspectives
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A dynamic perspective
The phases of the model over time
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A static perspective
The process activities that are enacted
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A practice perspective
Suggest good practices
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Phases in the RUP(1/4)
Four discrete phases
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Focus on business
Not technical concerns like the waterfall model
P has e i terati on
Incepti on
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Elaborati on
Cons tructi on
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Phases in the RUP(2/4)
Inception
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Goal
Establish a business case for the system
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Identify external entities (people and systems) and
define their interactions
Elaboration
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Goals
Develop an understanding of the problem domain
Establish an architectural framework for the system
Develop the project plan
Identify key project risks
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Phases in the RUP(3/4)
Construction
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Be concerned with system design, programming and
testing
Parts are developed in parallel and integrated
Transition
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From the development community to the user
community
Work in a real environment
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Phases in the RUP(4/4)
Iterations are supported in two ways
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Each phase may be enacted in an interactive
way
The whole set of phases may also be enacted
incrementally
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Static view of the RUP (1/2)
Activities (called workflows) during the
development process
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Six core workflows
Three core supporting workflows
Be oriented around associated UML models
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Static view of the RUP (2/2)
W ork flow
Descri ption
Business modelling
The business processes are modelled using business use cases.
Requirement s
Actors who interact with the system are ident ified and use cases are
developed to model the system requirement s.
Analysis and design
A design model is created and documented using architectural
models, component models, object models and sequ ence models.
Implementat ion
The components in the system are implemented and structured into
implementat ion sub-systems. Automat ic code generat ion from design
models helps accelerate this process.
Test
Test ing is an iterat ive process that is carried out in conjunct ion with
implementat ion. System test ing follows the completion of the
implementat ion.
Deployment
A product release is created, distributed to users and installed in their
workplace.
Configurat ion and
change management
This supporting workflow managed changes to t he 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.
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Good practice of the RUP
Develop software iteratively
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Deliver the highest priority system features early
Manage requirements
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Document requirements
Keep track of changes
Analyze the impact of changes
Use component-based architectures
Visually model software
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Graphical UML models (static and dynamic)
Verify software quality
Control changes to software
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Contents
4.1 Software process models
4.2 Process iteration
4.3 Process activities
4.4 The Rational Unified Process
4.5 Computer-Aided Software Engineering
4.6 Exercises
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4.5 Computer-Aided Software
Engineering
CASE
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Software used to support software process activities
Activity automation
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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.
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4.5 CASE
CASE technology has led to significant
improvements in the software process.
Limited by two factors:
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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.
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4.5.1 CASE classification
Different types of CASE tools and their support
for process activities.
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Functional perspective
Tools are classified according to their specific function.
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Process perspective
Tools are classified according to process activities that are
supported.
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Integration perspective
Tools are classified according to their organization into
integrated units.
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Functional 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
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Activity-based 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
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Implemen tatio n
Verification
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CASE categories
– from process perspective
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.
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Tools, workbenches and
environments
CASE
tech no lo g y
Wo rk ben ch es
To ols
Editors
Compilers
File
co mpar ato rs
Analy sis an d
d esign
Multi-metho d
wo rk ben ch es
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In teg rated
en v iro nmen ts
Pro grammin g
Sing le-meth od
wo rk ben ch es
Env iro nmen ts
Tes tin g
Gen er al-pu rp os e
wo rk ben ch es
Software processes
Pro ces s-cen tr ed
en v iro nmen ts
Lang u ag e-s pecific
wo rk ben ch es
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Contents
4.1 Software process models
4.2 Process iteration
4.3 Process activities
4.4 The Rational Unified Process
4.5 Computer-Aided Software Engineering
4.6 Exercises
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Exercises
None
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The End