SOEN341 - Estimation

experienced-based techniques

The estimate of future effort requirements is based on the manager’s experience of past projects and the application domain. Essentially, the manager makes an informed judgment of what the effort requirements are likely to be.

algorithmic cost modeling

In this approach, a formulaic approach is used to compute the project effort based on estimates of product attributes, such as size, and process characteristics, such as experience of staff involved.

experienced-based techniques

They rely on judgments based on experience of past projects and the effort expended in these projects on software development activities.

cost

It is estimated as a mathematical function of
product, project and process attributes whose
values are estimated by project managers:

• Effort = A * Size^B * M

• A is an organisation-dependent constant, B reflects the disproportionate effort for large projects and M is a multiplier reflecting product, process and people attributes.

The most commonly used product attribute is code size.

COCOMO cost modeling

It is an empirical model based on project experience. It is a well-documented, ‘independent’ model which is not tied to a specific software vendor.

application composition model

A sub-model in COCOMO 2 that is used when software is composed from existing parts. It supposed prototyping projects and projects where there is extensive reuse. It is based on standard estimates of developer productivity in application (object) points/month.

early design model

A sub-model in COCOMO 2 that is used when requirements are available but design has not yet started. This means that estimates can be made after the requirements have been agreed. It is based on a standard formula for algorithmic models. They are most useful for option exploration where you need to compare different ways of implementing the user requirements.

reuse model

A sub-model in COCOMO 2 that is used to compute the effort of integrating reusable components. It takes into account black-box code that is reused without change and code that has to be adapted to integrate it with new code.

There are two versions:

• black-box where code is not modified.

• white-box where code is modified. A size estimate equivalent to the number of lines of new source code is computed. This then adjusts the size estimate for new code.

post-architecture model

A sub-model in COCOMO 2 that is used once the system architecture has been designed and more information about the system is available. It uses the same formula as the early design model but with 17 rather than 7 associated multipliers.

The code size is estimated as:

• number of lines of new code to be developed.

• ESLOC: estimate of equivalent number of lines of new code computed using the reuse model.

• an estimate of the number of lines of code that have to be modified according to requirements changes.

multipliers

They reflect the capability of the developers, the non-functional requirements, the familiarity with the development platform, etc.

product attributes

It is a multiplier (AKA cost drivers) that are concerned with required characteristics of the software product being developed.

> reliability

computer attributes

It is a multiplier (AKA cost drivers) that are constraints imposed on the software by the hardware platform.

> memory constraint

personnel attributes

It is a multiplier (AKA cost drivers) that are multipliers that take the experience and capabilities of the people working on the project into account.

> experience

project attributes

It is a multiplier (AKA cost drivers) that are concerned with the particular characteristics of the software development project.

> tools used