Unit V _Software Engineering_21CSCST4050.pptx

Software
Engineering
UNIT V –
SOFTWARE
MAINTENANCE
10-08-2023
DR.M.PARTHIBAN, ASSOCIATE PROFESSOR, CSE
DEPARTMENT
1

Tables of Content
Software Maintenance, Maintenance Process
Models, Maintenance Cost, Software
Configuration Management
Software Reuse: What can be Reused? Why
almost no Reuse, Basic Issues in Reuse
Approach, Reuse at Organization level
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2

SOFTWARE
MAINTENANCE
 Software maintenance denotes any changes
made to a software product after it has been
delivered to the customer.
 On the other hand, software products do not
need maintenance on this count, but need
maintenance to correct errors, enhance
features, port to new platforms, etc.
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Types of Software
Maintenance
 Corrective: It is necessary either to rectify the bugs
observed while the system is in use.
 Adaptive: Adding new features to the existing code.
 Perfective: Typically made to improve the
maintainability of the code.
 Inspection: They are usually made as a result of
code inspection to reduce the likelihood of a failure.
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Maintenance Process
Models
 Two types of models for s/w maintenance is
proposed
 1st model – Small networks were the code is
changed directly and changes are reflected in the
relevant documents later.
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Maintenance Process
Models -1
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Maintenance Process
Models
 2nd model – The amount of rework required is
significant.
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Maintenance Process
Models -2
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Maintenance Cost
 Boehm [1981] proposed a formula for estimating
maintenance costs as part of his COCOMO cost
estimation model.
 Boehm’s maintenance cost estimation is made
in terms of a quantity called the annual change
traffic (ACT).
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Maintenance Cost
 Annual Change Traffic (ACT)
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 The annual change traffic (ACT) is multiplied
with the total development cost to arrive at
the maintenance cost:
Maintenance cost = ACT × Development cost

Maintenance Cost
 Most maintenance cost estimation models, give
only approximate results because they do not
take into account several factors such as
 experience level of the engineers, and
 familiarity of the engineers with the product,
 hardware requirements,
 software complexity, etc.
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Software Configuration
Management
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 The configuration of the software is the state
of all project deliverables at any point of time;
and software configuration management
deals with effectively tracking and controlling
the configuration of a software during its life
cycle.

Necessity of Software
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 Problems associated with concurrent access
 Providing a stable development environment
 System accounting and maintaining status
information
 Handling variants

Management Activities
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Configuration identification
Configuration control

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 Configuration identification
 Project managers normally classify the
objects associated with a software
development into three main categories—
Controlled,
Pre-controlled, and
Uncontrolled.

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 Controlled objects are those that are
already under configuration control.
 Pre-controlled objects are not yet under
configuration control, but will eventually be
under configuration control.
 Uncontrolled objects are not subject to
configuration control.

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 Controllable objects include both controlled and pre-
controlled objects. Typical controllable objects include:
 Requirements specification document
 Design documents
 Tools used to build the system, such as compilers,
linkers, lexical analyzers, parsers, etc.
 Source code for each module
 Test cases
 Problem reports

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 Configuration control allows only authorized changes to
the controlled objects to occur and prevents unauthorized
changes.
 In order to change a controlled object such as a module, a
developer can get a private copy of the module by a reserve
operation (see in the Figure).
 Configuration management tools allow only one person to
reserve a module at any time.
 Once an object is reserved, it does not allow any one else to
reserve this module until the reserved module is restored.

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DEPARTMENT
19

Tables of Content
Software Maintenance, Maintenance Process
Models, Maintenance Cost, Software
Software Reuse: What can be Reused? Why
almost no Reuse, Basic Issues in Reuse
Approach, Reuse at Organization level
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DEPARTMENT
20

Software Reuse
 Software products are expensive.
 A possible way to reduce development cost
is to reuse parts from previously developed
software.
 A reuse approach that is of late gaining
prominence is component-based
development.
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What can be reused?
 The prominent items that can be effectively
reused are:
 Requirements specification
 Design
 Code
 Test cases
 Knowledge
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Why almost no reuse
so far?
 Engineers feeling that the current system that
they are developing is similar to the last few
systems built.
 No attention is paid on how not to duplicate
what can be reused from previously
developed systems.
 Everything is being built from scratch.
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Why almost no reuse
so far?
 Creation of components that are reusable in
different applications is a difficult problem.
 It is very difficult to anticipate the exact
components that can be reused across
different applications.
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Why almost no reuse
so far?
The following observation is significant:
 Mathematical libraries are being reused
 No one in their mind would think of writing
a routine to compute sine or cosine.
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Basic issues in any
reuse program
The following are some of the basic
issues that must be clearly understood
for starting any reuse program:
 Component creation.
 Component indexing and storing.
 Component search.
 Component understanding.
 Component adaptation.
 Repository maintenance.
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Basic issues in any
reuse program
 Component creation - the reusable components
have to be first identified. Selection of the right kind of
components having potential for reuse is important.
 Component indexing and storing - Indexing
requires classification of the reusable components so
that they can be easily searched when we look for a
component for reuse. The components need to be
stored in a relational database management system
(RDBMS) or an object-oriented database system
(ODBMS) for efficient access when the number of
components becomes large.
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Basic issues in any
reuse program
 Component search - The programmers
need to search for right components matching
their requirements in a database of
components.
 Component understanding - The
programmers need a precise and sufficiently
complete understanding of what the
component does to be able to decide whether
they can reuse the component.
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Basic issues in any
reuse program
 Component adaptation - Often, the components
may need adaptation before they can be reused,
since a selected component may not exactly fit the
problem at hand.
 Repository maintenance - A component
repository once is created requires continuous
maintenance. New components, as and when
created have to be entered into the repository. The
faulty components have to be tracked.
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Basic issues in any
Reuse Approach
 A promising approach that is being adopted by
many organizations is to introduce a building block
approach into the software development process.
 Domain Analysis
 Component Classification
 Searching
 Repository Maintenance
 Reuse without Modifications
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Basic issues in any
Reuse Approach
 Domain Analysis:
 The aim of domain analysis is to identify the reusable
components for a problem domain.
1. Reuse domain
2. Evolution of a reuse domain
1. Reuse domain – Application Areas
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Basic issues in any
Reuse Approach
2. Evolution of a reuse domain - The ultimate results
of domain analysis is development of problem oriented
languages. The problem-oriented languages are also
known as application generators.
 Stage 1 : There is no clear and consistent set of notations.
 Stage 2 : Here, only experience from similar projects are
used in a development effort.
 Stage 3: At this stage, the domain is ripe for reuse.
 Stage 4: The domain has been fully explored.
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Basic issues in any
Reuse Approach
 Component Classification
 Properly classified in order to develop an effective
indexing and storage scheme
 Hardware reuse has been very successful
 At the lowest level, the components are described
in several forms — natural language, description,
logic schema, timing information, etc.
 The higher the level at which a component is
described, the more is the ambiguity.
 This has motivated the Prieto-Diaz’s
classification scheme.
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Basic issues in any
Reuse Approach
 Prieto-Diaz’s classification scheme
 Each component is best described using a
number of different characteristics or facets.
 For example, objects can be classified using
the following:
 Actions they embody.
 Objects they manipulate.
 Data structures used.
 Systems they are part of, etc.
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Basic issues in any
Reuse Approach
 Searching
 A popular search technique that has proved to be
very effective is one that provides a web interface
to the repository.
 Using such a web interface, one would search an
item using an approximate automated search
using key words, and then from these results
would do a browsing using the links provided to
look up related items.
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Basic issues in any
Reuse Approach
 Searching
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Basic issues in any
Reuse Approach
 Searching
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Unit V _Software Engineering_21CSCST4050.pptx

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