Software Evolution and Maintenance Models

Software Evolution and Maintenance
Chapter 3
Evolution and Maintenance Models

outline
• 1. General Idea
• 2. Reuse Oriented Model
• 2.1 Quick fix model
• 2.2 Iterative enhancement model
• 2.3 Full reuse model
• 3. Software Maintenance Life Cycle
models
• 3.1 The staged model
• 3.1.1 The staged model for CSS
• 3.1.2 The staged model for FLOS
• 3.2 Change Mini-Cycle Model
• 4. Software Maintenance Standard
• 4.1 IEEE/EIA 1219 Maintenance Process
• 4.2 ISO/IEC 14764 Maintenance Process

1. General Idea
• One traditional software development life cycle (SDLC) is shown in Figure, which
comprises two discrete phases, namely:
• Development
• Maintenance
• Maintenance approaching two-thirds of the product life-span.
• The percentages in Figure 3.1 indicate relative costs.

Software maintenance has unique characteristics:
• Constraints of an existing system: Maintenance is performed on an operational system. Therefore, all
modifications must be compatible with the constraints of the existing architecture, design, and code.
• Shorter time frame: A maintenance activity may span from a few hours to a few months, whereas software
development may span one or more years.
• Available test data: In software development, test cases are designed from scratch, whereas software
maintenance can select a subset of these test cases and execute them as regression tests.

2. Reuse Oriented Models
• One obtains a new version of an old system by modifying one or several
components of the old system and possibly adding new components.
• The three process models for maintenance:
Quick fix model:
The changes are quickly made to the
code and then to the accompanying
documentation
Iterative enhancement model:
First changes are made to the
highest level documents. Eventually,
changes are propagated down to the
code level
Full reuse model:
A new system is built from components
of the old system and others available in
the repository

2.1 Quick Fix Model
1. Source code is modified to fix the problem.
2. Necessary changes are made to the relevant
documents.
3. The new code is recompiled to produce a
new version.
Often changes to the source code are made with
no prior investigation such as analysis of
impact of the changes, ripple effects of the
changes, and regression testing.
Figure 3.2 The quick fix model ©IEEE, 1990

2.2 Iterative enhancement model
The iterative enhancement model, explained in Figure
3.3, shows how changes flow from the very top level
documents to the lowest-level documents.
The model works as follows:
1. It begins with the existing system’s artifacts, namely,
requirements, design, code, test, and analysis
documents.
2. It revises the highest-level documents affected by the
changes and propagates the changes down through
the lower-level documents.
3. The model allows maintainers to redesign the
system, based on the analysis of the existing system.
Figure 3.3
The iterative enhancement model
©IEEE, 1990

2.3 Full reuse model
• The main assumption in this model is
the availability of a repository of
artifacts describing the earlier versions
of the systems.
• In the full reuse model, reuse is
explicit and the following activities are
performed.
Figure 3.4 The full reuse model ©IEEE, 1990

3. Software Maintenance Life Cycle models

CSS Vs. FLOSS
• Free/Libre and Open Source Software(FLOSS) is
distributed under a licensing agreement which
allows computer code to be shared, viewed and
modified by other users and organizations.
• open source software is available for the general
public to use and modify from its original design
free of charge
• Closed source software (CSS)can be defined as
proprietary software distributed under a
licensing agreement to authorized users with
private modification, copying, and republishing
restrictions. Or in layman terms, the source
code is not shared with the public for anyone to
look at or change

3.1.1 The Staged Model for CSS
• Their model divides the lifespan of a typical system into four stages:
• Initial development – The first delivered version is produced. Knowledge about the system is fresh and
constantly changing. In fact, change is the rule rather than the exception. Eventually, an architecture
emerge and stabilizes.
• Evolution – Simple changes are easily performed and more major changes are possible too, albeit the
cost and risk are now greater than in the previous stage. Knowledge about the system is still good,
although many of the original developers will have moved on. For many systems, most of its lifespan is
spent in this phase.
• Servicing – The system is no longer a key asset for the developers, who concentrate mainly on
maintenance tasks rather than architectural or functional change. Knowledge about the system has
lessened and the effects of change have become harder to predict. The costs and risks of change have
increased significantly.
• Phase out – It has been decided to replace or eliminate the system entirely, either because the costs of
maintaining the old system have become prohibitive or because there is a newer solution waiting in the
pipeline. An exit strategy is devised and implemented, often involving techniques such as wrapping and
data migration. Ultimately, the system is shut down.

Figure 3.5 The simple staged model for the CSS life cycle ©IEEE, 2000

Figure 3.6 The versioned staged model for the CSS life cycle ©IEEE, 2000

3.1.2 The Staged Model for FLOSS
Three major differences are identified between CSS systems and FLOSS systems.
• In Figure 3.7, the rectangle with the label “Initial development” has been visually highlighted
because it can be the only initial development stage in the evolution of FLOSS systems. In other
words, it does not have any evolution track for FLOSS system.
• With some systems that were analyzed, after a transition from Evolution to Servicing, a new period of
evolution was observed. This possibility is depicted in Figure as a broken arc from the Servicing stage
to the Evolution stage.
In general, the active developers of FLOSS systems get frequently
replaced by new developers. Therefore, the dashed line in Figure
exhibits this possibility of a transition from Phaseout stage to
Evolution stage.
Figure 3.7 The staged model for
FLOSS system ©ACM, 2007

3.2 Change Mini-Cycle Model
Software change is a process that may introduce new
requirements to the existing system, or may need to alter
the software system if requirements are not correctly
implemented. In order to capture this, an evolutionary
model known as change mini-cycle.
Figure 3.8 The change mini-cycle ©Springer, 2008

4. Software Maintenance Standard
• IEEE and ISO have both addressed s/w maintenance processes.
• IEEE/EIA 1219 and ISO/IEC 14764 as a part of ISO/IEC12207
(life cycle process).
• ISO/IEC 14764 describes s/w maintenance as an iterative process
for managing and executing software maintenance activities.

4.1 IEEE/EIA 1219 Maintenance Process
The standard focuses on a seven-phases:
• Problem Identification.
• Analysis.
• Design.
• Implementation.
• System Test.
• Acceptance Test.
• Delivery.
Figure 3.9 Seven phases of IEEE maintenance
process ©IEEE, 2004

4.2 ISO/IEC 14764 Maintenance Process
The maintenance process comprises the following high level
activities:
1. Process Implementation.
2. Problem and Modification Analysis.
3. Modification Implementation.
4. Maintenance Review and Acceptance.
5. Migration.
6. Retirement.
Figure 3.17 ISO/IEC 14764 iterative
maintenance process ©IEEE, 2004

Speaker Information
 Moutasm tamimi
 Masters of Software Engineering
 Independent Consultant , IT Researcher.
 CEO at ITG7.com , IT-CRG.com
 Email: tamimi@itg7.com,
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