Transcript 1407993664_software_evolution

Introduction to Software Evolution and
Maintenance
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Importance of evolution
 Organizations have huge investments in their software
systems - they are critical business assets.
 To maintain the value of these assets to the business, they
must be changed and updated.
 The majority of the software budget in large companies is
devoted to evolving existing software rather than developing
new software.
 Studies indicate that up to 75% of all software professionals
are involved in some form of maintenance/evolution activity.
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Software change
 Software change is inevitable
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New requirements emerge when the software is used;
The business environment changes;
Errors must be repaired;
New computers and equipment is added to the system;
The performance or reliability of the system may have to be
improved.
 A key problem for organizations is implementing and
managing change to their existing software systems.
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Types of changes
 Repair software faults
 Changing a system to correct deficiencies in the way meets its
requirements.
 Adapt software to a different operating environment
 Changing a system so that it operates in a different environment (computer,
OS, etc.) from its initial implementation.
 Add to or modify the system’s functionality
 Modifying the system to satisfy new requirements.
 Improve the program structure and system performance
 Rewriting all or parts of the system to make it more efficient and
maintainable.
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Software evolution and
software maintenance
 No standard definitions.
 Broad definition of evolution: Generally, software evolution refers to the study
and management of the process of making changes to software over time.
 In this definition, software evolution comprises:
 Development activities
 Maintenance activities
 Reengineering activities
 Narrow definition of evolution: Sometimes, software evolution is used to refer
to the activity of adding new functionality to existing software.
 Maintenance refers to the activity of modifying software after it has been put to
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use in order to maintain its usefulness.
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“Reengineering”
“Evolution”
“Maintenance”
Types of changes
 Repair software faults
 Changing a system to correct deficiencies in the way meets its
requirements.
 Adapt software to a different operating environment
 Changing a system so that it operates in a different environment (computer,
OS, etc.) from its initial implementation.
 Add to or modify the system’s functionality
 Modifying the system to satisfy new requirements.
 Improve the program structure and system performance
 Rewriting all or parts of the system to make it more efficient and
maintainable.
History
 1960s – 1970s
 Inclusion of maintenance in waterfall lifecycle after delivery of the software
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product.
 Perception that post-delivery activities only consisted of bug fixes and minor
adjustments.
 Did not account for the need to add functionality due to new and changed
requirements.
 1970s
 Lehman postulated the initial laws of program evolution.
 Stressed the need for continuous evolution due to changes in the software’s
operational environment.
 Late 1970s – 1980s
 Initial process models that handled change requests.
 1990s
 General acceptance of software evolution.
 Development of new process models that accounted for evolution activities:
evolutionary development, spiral model, agile software development.
Evolution processes
 Processes for evolving a software product depend on
 The type of software being maintained;
 The development processes used;
 The skills and experience of the people involved.
 Proposals for change are the drivers for system evolution.
Change identification and evolution continue throughout the
system lifetime.
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Change identification and evolution
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The system evolution process
Change
requests
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Impact
analysis
Release
planning
Change
implementation
Fault repair
Platform
adaptation
System
enhancement
System
release
Change implementation
Proposed
changes
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Requirements
analysis
Requirements
updating
Software
development
Legacy systems
 For many systems, the software evolution process is not as straightforward as
described.
 Associated models and documentation of the software may be missing or
hopelessly outdated.
 The new requirements may not be anticipated by the design of the software,
making the resulting changes difficult to implement correctly.
 Legacy systems are old systems that have become significantly difficult to
modify.
 Accumulation of changes have eroded the modularity of the original design.
 The documentation has not been maintained and has become obsolete.
 One or more pieces of its underlying technologies have become obsolete.
 Two complementary techniques are employed to support the continued
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evolution of legacy systems:
 Reverse engineering.
 Reengineering.
Obsolete system components
 Hardware - may be obsolete mainframe hardware.
 Support software - may rely on support software from suppliers
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who are no longer in business.
Application software - may be written in obsolete programming
languages.
Application data - often incomplete and inconsistent.
Business processes - may be constrained by software structure and
functionality.
Business policies and rules - may be implicit and embedded in the
system software.
Reverse engineering
 In many legacy systems, the only reliable information about the
system is the source code.
 Reverse engineering reconstructs requirements, design models,
test cases and user documentation consistent with the current
state of the source code.
 Reverse engineering encompasses several activities: program
comprehension, software visualization, static and dynamic slicing,
etc.
 Reverse engineering is often the initial activity in a reengineering
project.
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System reengineering
 Rewriting parts or all of a legacy system to make it more
evolvable, so that it can more easily accommodate future change
requests.
 Some authors [e.g., Sommerville] define it more strictly as the process of
restructuring legacy software without changing its functionality.
 Others include a forward engineering phase as part of reengineering.
 Reengineering is applicable where some but not all sub-systems of
a larger system require frequent maintenance.
 Reengineering involves adding effort to make them easier to
maintain. The system may be restructured and redocumented.
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Advantages of reengineering
 Reduced risk
 There is a high risk in new software development. There may be
development problems, staffing problems and specification
problems.
 Reduced cost
 The cost of re-engineering is often significantly less than the
costs of developing new software.
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The reengineering process
Program
documentation
Original
program
Modularized
program
Original data
Reverse
engineering
Program
modularization
Source code
translation
Data
re-engineering
Program
structure
improvement
Structured
program
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Re-engineered
data
Reengineering process activities
 Source code translation
 Convert code to a new language.
 Reverse engineering
 Analyze the program to understand it;
 Program structure improvement
 Restructure automatically for understandability;
 Program modularization
 Reorganize the program structure;
 Data reengineering
 Clean-up and restructure system data.
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Research landscape
 Two aspects of software evolution research
 Reverse engineering and reengineering techniques
 Techniques for dealing with change
 Process and change management
 Evolution of software artifacts
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Two aspects of software evolution
 “What and why”
 Focuses on software evolution as a scientific discipline.
 Studies the nature of the software evolution phenomenon to understand its
driving factors.
 Key interests include the formulation and refinement of fundamental
theories and laws of software evolution.
 “How”
 Focuses on software evolution as an engineering discipline.
 Studies how to support the daily tasks of the software developer or project
manager.
 Key interests include the development and validation of tools and techniques
to guide, implement and control software evolution.
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Techniques for dealing with change
 Program comprehension
 Understanding the existing program in order to change it.
 Change impact analysis
 Identification of the parts of the system that will be affected by a proposed
change.
 Change propagation
 Making sure that all affected parts are changed correctly.
 Restructuring/Refactoring
 Improving the software structure or architecture without changing the
behavior.
 Regression testing
 Efficiently verifying that the change preserved the behavior of functionalities
that should not be impacted.
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Management
 Economics of software evolution
 Developing economic models to support evolution-related management
decisions.
 Comparing the cost of different strategies for changes.
 Assessing the cost-benefits of investing in reengineering.
 Software metrics
 Measuring the quality of a change.
 Measuring the degree of modularity.
 Configuration management
 Change management processes.
 Management of multiple versions.
 Merging versions together.
 Release management.
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Evolution of software artifacts
 Requirements evolution
 Managing requirements changes.
 Architecture evolution
 Reengineering the architectures of legacy systems.
 Migration to distributed architectures, e.g., service-oriented architectures.
 Maintenance issues with modern architectures.
 Design evolution
 Evolution of design models.
 Test case evolution
 Adding and modifying test cases to verify that the system behavior was
changed as intended.
 Traceability management
 How to assure the consistency of the different artifacts.
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Other evolution issues
 Data evolution
 Migrating to a new database schema.
 Verifying that the information in the existing databases are preserved.
 Runtime evolution
 How to modify a system without stopping it.
 Encompasses runtime reconfiguration, dynamic adaptation, dynamic
upgrading.
 Language evolution
 Dealing with changes in the programming language definition.
 Especially an issue in multi-language systems.
 Designing languages to make them more robust to evolution.
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