Estimation - Software Cost Estimation & Line Of Code (LOC)

Estimation

Software cost estimation is the process of predicting the effort required to develop a software system. Software measurement, just like any other measurement in the physical world, can be categorized into Direct measures and Indirect measures.

Direct measures of the software process include measurement of cost and effort applied. Direct measures of a product also include Line Of Code (LOC) produced, execution speed, memory size, and defects reported over some of times.

Indirect measures of the software process include measurement of resulting features of the software. Indirect measures of the product also include its functionality, quality, complexity, usability etc.

On the other word, estimation is not an exact science. Too many variables – human, technical, and environment – can affect the ultimate cost of software and effort applied to develop it.

In order to make a reliable cost and effort estimation, there are a lot of techniques that provide estimates with acceptable amount of risk.

These methods can be categorized into-

a) Decomposition techniques

            I) Lines Of Code (LOC)

            II) Functional Point (FP) Estimation

b) Empirical Estimation models

            I) COnstructive COst MOdel (COCOMO)  

                        1. Basic COCOMO

                        2. Intermediate COCOMO

                        3. Advanced COCOMO

                 

Line Of Code (LOC)

LOC is a direct approach method and requires a higher level of detail by means of decomposition and partitioning. From statement of software scope, software is decomposed into problem functions that can each be estimated individually. LOC is then calculated for each function.

An expected value is then computed using the following formula-

EV = ( S_opt + 4S_m + S_pess) / 6

where

EV stand for the Estimation Variable

S_opt stand for Optimistic Estimation case when everything goes right

S_m stand for the most likely Estimation case given normal problems and opportunities

S_pess stand for the pessimistic Estimation case where everything goes wrong

Once the expected value for estimation variable has been determined, historical LOC or FP data are applied and person months, costs etc. are calculated using the following formula

Productivity = KLOC / Person-month

Quality = Defects / KLOC
Cost = $/LOC

Documentation = pages of documentation / KLOC

Where,

KLOC stand for number of code (in thousands)

Person-month stand for is the time (in months) taken by developers to finish the product

Defects stand for Total Number of errors discovered.

Example:

Problem Statement: Take our Library management system case. Software developed for library will accept data from operator for issuing and returning books. Issuing and returning will require some validity checks. For issue it is required to check if the member has already issued the maximum books allowed. In case for return, if the member is returning the book after the due date then fine has to be calculated. All the interactions will be through user interface. Other operations include maintaining database and generating reports at regular intervals.

Major software functions identified

1. User interface

2. Database management

3. Report generation

For user interface

S_opt : 1800

S_m  :2000

S_pess : 4000

EV for user interface

EV = (1800 + 4*2000 + 4000) / 6

EV = 2300

For dababase managemant

S_opt : 4600

S_m  : 6900

S_pess : 8600

EV for database management

EV = (4600 + 4*6900 + 8600) / 6

EV = 6800

For report generation

S_opt : 1200

S_m  : 1600

S_pess : 3200

EV for database management   report generation

EV = (1200 + 4*1600 + 3200) / 6

EV = 1800

Function	Estimated LOC
User interface	2300
Database management	6800
Report generation	1800
Estimated LOC	10900

Suppose productivity = 3000 LOC / person-month

Development Cost = $8000 person-month

Person-month = LOC / Productivity

                        = 10900/3000

                                    = 3.6

Cost of software = Development Cost * person-month

                                       = 8000 * 3.6

                                         = 29120

Cost = Cost of software ($) / LOC

= 29120 / 10900

     = 2.67 $ / LOC