In Software Engineering under Software cost estimation

1. BY
K.LALITHAMBIGA
IIMsc(Computer Science & Information Technology)
Department of CS&IT
NS College of Arts and Science
Theni.

2.  Software maintenance typically requires 40 to 60 percent, and in
some cases as much as 90 percent, of the total lifecycle effort
devoted to a software product.
The major concerns about maintenance during the
planning phase of a software projects are estimating the
number of maintenance programmers that will be
needed and specifying the facilities required for
maintenance.
A widely used rule of thumb for the distribution of
maintenance activities is
60% -Enhancement
20% -Adaptation
20% -Corrections

3.  In survey 487 business data processing installations, Lientz and
Swanson determined that typical level of effort devoted to
software maintenance was around
FOR EXAMPLE:
 If a maintenance programmer can maintain 32KDSI, then two a
maintenance programmers are required to main 64 KDSI:
FSPm=(64KDSI)/(32 KDSI/FSP)=2 FSPm
50% of total lifecycle effort,
The distribution of maintenance activities was
51.3% for enhancement ,
23.6% for adaptation,
21.7% for repair and
3.4% for others(LIE80).

4.  Boehm suggests that maintenance effort can be activity ratio ,
which is the number of source instruction to be added and
modified in any given time period divided by the total number of
instructions:
 Number of programmer –months required for maintenance in the
corresponding time period:
 In enhancement is provided by an effort adjustment factor EAF,
which recognizes that the effort multipliers for maintenance may
be different from the effort multipliers used for development:
ACT=(DSIadded+DSImodified)/DSItotal
PMm=ACT *MMdev
PMm=ACT *EAF*MMdev

7.  Heavy emphasis on reliability and the use of modern
programming practices during development may reduce the
amount of effort required for maintenance, while low emphasis on
reliability and modern practices during development may
increase the difficulty of maintenance.
FSP - Fulltime Software Personnel
KSDI -Kilo delivered Source Instruction
ACT -Activity ratio
DSI -Delivered Source Instruction
PM -Programmer Months
EAF -Effort Adjustment Factor