Software maintenance

SOFTWARE MAINTENANCE
BY,
K.RAJALAKSHMI
II-MSC(IT)
DEPARTMENT OF CS&IT
NADAR SARASWATHI COLLEGE OF ARTS AND SCIENCE,THENI

SYNOPISIS:
 Introduction
 Enhancing Maintainability during
development
 Managerial aspects of Software Maintenance
 Configuration management
 source-code metrics
 Other maintenance tools & techniques

Introduction:
 The term ”software maintenance” is used to
describe the software engineering activities that
occur following delivery of a software product to
the customer
 The development cycle for a software product
span 1 or 2 years , while the maintenance phase
span 5 to 10 years
 Maintenance activities involve making
enhancement to software product , adapting
products to new environment and correcting
problem

 It is well established that maintenance
activities consume a large potion of the total
life cycle budget(LIE80)
 It is not uncommon for software maintenance
to account for 70 % of total software life cycle
cost
 Analysis activities during software
maintenance involve understanding the
scope and effort of a desire changes as well as
the constraints on making the change

Enhancing Maintainability
during development
 Many activities performed during software
development enhance the maintenance
ability of a software products
Analysis activity:
Architectural design activities
Detailed design activities
Implementation activities
Supporting document

Analysis activities:
 Develop standard and guidelines
 Set milestone for the supporting document
 Specify quality assurance procedures
 Identify likely product enhancements
 Determine resource required for
maintenance
 Estimate maintenance costs

Architectural design
activities:
 Emphasize clarity and modularity as design
criteria
 Design to ease likely enhancement
 Use standardized notation to document data
flow
 Function ,structure , and interconnection
 Observe the principles of information hiding ,
data abstraction and top-down hierarchical
decomposition

Detailed design activities:
 Use standardized notation to specify
algorithms
 data structure and procedure interface
specifications specify side effects and
exception handling for each routine
 Provide cross-reference directories

Implementation activities:
 Use single entry, single exit constructs
 Use standard indentation of constructs
 Use simple , clear coding style
 Use symbolic constants to parameterize
routine
 Follow standard internal commenting
guidelines

Supporting document:
 There are two particular important
supporting document that should be
prepared during the software development
cycle in order to ease maintenance activities
 Develop a maintenance guide
 Develop a test suite
 Provide test suite documentation

Managerial aspects of
Software Maintenance
 One of the most important aspect of
software maintenance involves tracking and
control of maintenance activities
 Maintenance activity for a software product
usually occur in response to a change request
filed by a user of the product

Types managerial aspects of
Software maintenance
 Change control board
 Change request summaries
 Quality assurance activities
 Organizing maintenance programmers

Change control board
 The change control board reviews and
approves all change request.
 The board may deny a request , recommend
a modified version of the change or approve
the change as submitted.
 Important aspect of this structure are the
shielding of maintenance programmer from
continual interruption by users and the
guidance provided to the programmer and
analytics by the change control board .

Quality assurance activities
 In many organization , the quality assurance
group monitor change request , prepares change
request summaries , perform regression testing
of software modification , provides configuration
management
 Retrains and protest the physical media for
software products.
 The quality assurance group should be
represented on change control board and should
have sign-off authority for new releases.

Organizing maintenance
programmer
 Software maintenance can be performed by
development team or by member of a
separate organization ;there are advantages
and disadvantages to both approaches
 Organizing maintenance programming is to
periodically rotate programmer between
development and maintenance
 The primary disadvantages of this approach
is overhead cost incurred in rotating
personnel among different task.

Configuration management
 It is concerned with tracking and controlling of
the work products that constitute a software
products.
 Five laws of program evolution :
o CONTINUING CHANGE
o INCREASING COMPLEXITY
o FUNDAMENTAL LAW OF PROGRAM
EVOLUTION
o CONVERVATION OF ORGANIZATION
STABILITY
o CONVERVATION OF FAMILIARITY

Configuration management
data base
 Software tools to support configuration
management include configuration
management data base and version control
library system
 A configuration management data base can
provide information concerning product each
product structure , current revision number,
current status and change request history for
each product version

Version control libraries
 A version control library may be part of a
configuration management data base or it
may be used as a stand- alone tool.
 A configuration management data base
provide a macro view of a product family,
while a version control library controls the
various files that constitute the various
version of software products

Source – code metrics
 During the past few years , a great deal of
effort has been expended on developing
metrics to measure the complexity of source
code.
 Properties of source code , such as the
number of operation and operands , the
complexity of the control flow graphs , the
number of parameter and global variables in
routines

Two main source code metrics
 Halsted’s effort equation
 Mc Cabe’s cyclomatic complexity measure

Halsted’s effort equation:
 Halsted developed a number of metrics that
are computed from easily obtained properties
of the source code
 These properties including the total number
of operation in a program , N1; the total
number of operand , N2 ; the number of
unique operator ,n1 ; and the number of
unique operand ,n2
 FORTRAN routine & associated values of
N1,N2,n1,and n2

 Halsted defines several quantities using these
number. For example , program length N is
defined as N1+N2;(N1+N2=50)
 Halsted’s estimator of program length is :
N=n1 log2 n1 + n2 log2 n2
For example :
N= 10(3.2) + 7(2.8)=52.9
Program volume is define as
V= (N1+ N2) log2 (n1+n2)

 And language level ( the level of language
abstraction ) is
L=(2*n2)/(n1+N2)
Program effort is defined asVL:
E=(n1*N2*(N1+N2)*log2(n1+n2))/(2*n2)

Mc Cabe’s cyclomatic metric:
 Mc Cabe has observed that the difficulty of
understanding a program is largely
determined by the complexity of the control
flow graph for that program
 The cyclomatic numberV of a connected
graph G is the number of linearly independent
path in graph .
 V(G) is computed as follow:

V(G) =E-n+2p
 Where E is the number of edges
n is the number of nodes
p is the number of connected
components
V(G) is 5 for e.g. , the dashed line connecting
output node f to input node a is added to
produce a connected graph

 Mc Cabe observes that for a structured
program with every single entry l single exit
construct ,V equals the number of predicate
plus one
 Also provided G is planar ,V is equal to the
number of region inG.

Other maintenance tools &
techniques
 Software maintenance is a microcosm of
software development, the activities that a
software maintainer may become involved in
span the entire spectrum of software
engineering
 Automated tools for software maintenance:
text editor
Debugging aids
cross reference generator
linkage editor
comparator etc.,.

Software maintenance

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