Empirical Estimation with Examples & COnstructive COst MOdel

 Resource models consist of one or more empirically derived equations. These equations are used to predict effort (in person-month), project duration, or other pertinent project data. There are four classes of resource models:

·         Static single-variable models

·         Static multi-variable models

·         Dynamic multi-variable models

·         Theoretical models

The basic version of the COnstructive COst MOdel or COCOMO is an example of a static single-variable model. Barry Boehm introduced COCOMO models.

There is a hierarchy of these models.

                                              

COCOMO applies to three classes of software projects:

·      Organic projects - "small" teams with "good" experience working with "less than rigid" requirements

·      Semi-detached projects - "medium" teams with mixed experience working with a mix of rigid and less than rigid requirements

·      Embedded projects - developed within a set of "tight" constraints. It is also combination of organic and semi-detached projects.(hardware, software, operational, ...)

The basic COCOMO equationstake the form:

E = a_b  * (KLOC) b^b

D = c_b  * (E) ^db

Effort Applied (E) = a_b(KLOC)b^b[ person-months ]

Development Time (D) = c_b(Effort Applied)db[months]

People required (P) = Effort Applied / Development Time [count]

Where, KLOC is the estimated number of delivered lines (expressed in thousands) of code for project. The coefficients ab, bb, cb and db are given in the following table:

Project class	ab	bb	cb	db
organic	2.4	1.05	2.5	0.38
semidetached	3.0	1.12	2.5	0.35
embedded	3.6	1.20	2.5	0.3

Example:

Use the information given in the table below

Project Class	ab	bb	cb	db
Organic	2.4	1.05	2.5	0.38
Semidetached	3.0	1.12	2.5	0.38
Embedded	3.6	1.20	2.5	0.12

Assume that the expected size of an organic software project is 45.6 KLOC. Using the coefficients in the above table and the BASIC COCOMO MODEL, calculate the recommended number of people needs to be engaged to complete the project.

Effort Applied (E) = a_b  * (KLOC) b^b

= 2.4 * (45.6) ^1,05

= 132.47

Development Time (D) = c_b  * (E) ^db

= 2.5 *(132.47) ^0.38

= 2.5 * 6.4

= 16

People Required (P) = E/D

= 132.47/16

= 8.27

= 9 people

The Intermediate Cocomo formula takes the form:

E=ai(KLoC)(bi).EAF

Where E is the effort applied in person-months, KLOC is the estimated number of thousands of delivered lines of code for the project, and The product of all effort multipliers results in an effort adjustment factor (EAF).The coefficient ai and the exponent bi are given in the next table. And the ci value is always 2.5.

Software project	ai	bi
Organic	3.2	1.05
Semi-detached	3.0	1.12
Embedded	2.8	1.20

The Development time D calculation uses E in the same way as in the Basic COCOMO.

Example:

Consider an organ project where three module to implement. User interfaces 0.10 KLOC, database management 0.8 KLOC and report generation 0.18 KLOC. Efforts and project class value as follows:

Software project Class	ai	bi	di
Organic	3.2	1.05	1.05
Semi-detached	3.0	1.12	1.12
Embedded	2.8	1.20	1.20

Cost Drivers	Level	Effort Adjustment Factor
Complexity	High	1.15
Storage	High	1.06
Experience	Low	1.13
Programming Capabilities	Low	1.17
Analyst capability	High	1.23
Memory Constraints	Low	1.01

Calculate the effort applied in person-month using Intermediate COCOMO Model. What will be total development time and how many people should be hired?

Solution:

Effort (E) =a_i(KLOC)(bi)EAF

   = 3.2 (0.10 + 0.8 + 0.18)^1.05 * (1.15* 1.06* 1.13* 1.17*1.23*1.01)

   = 3.2 * 1.08 ^1.05 * 2.002

  = 6.945

Development Time, D = c_b  * (E) ^db

                                   = 2.5 * 6.945^1.05

                                                   = 19.129

People, N = E/D = 6.945/19.129 = 0.36