Background:
Software Cost Estimation is widely considered to be a weak link in software project management. It requires a significant amount of effort to perform it correctly. Errors in Software Cost Estimation can be attributed to a variety of factors. Various studies in the last decade indicated that 3 out of 4 Software projects are not finished on time or within budget or both.
Who is responsible for Software Cost Estimation?
The group of people responsible for creating a software cost estimate can vary with each organization. However the following is possible in most scenarios -
- People who are directly involved with the implementation are involved in the
..estimate.
- Project Manager is responsible for producing realistic cost estimates.
- Project Managers may perform this task on their own or consult with
..programmers responsible.
- Various studies indicate that if the programmers responsible for development
..are involved in the estimation it was more accurate. The programmers have
..more motivation to meet the targets if they were involved in the estimation
.. process.
Following scenarios are also possible
- An independent cost estimation team creates an Estimate
- Independent Experts are given the Software specification and they create a
..Software Cost estimate. The Estimation team reviews this and group
.. consensus arrives at a final figure.
Factors contributing to inaccurate estimation
• Scope Creeps, imprecise and drifting requirements
• New software projects pose new challenges, which may be very different from
..the past projects.
• Many teams fail to document metrics and lessons learned from past projects
• Many a times the estimates are forced to match the available time and
..resources by aggressive leaders
• Unrealistic estimates may be created by various ‘political under currents’
Impact of Under-estimating:
Under-Estimating a project can be vary damaging
- It leads to improper Project Planning
- It can also result in under-staffing and may result in an over worked and
..burnt out team
- Above all the quality of deliverables may be directly affected due insufficient
..testing and QA
- Missed Dead lines cause loss of Credibility and goodwill
The Estimation Process:
Generally the Software Cost estimation process comprises of 4 main steps:
1) Estimate the size of the development product.
This comprises of various sub-steps or sub tasks. These tasks may have been done already during Requirement Analysis phase. If not then they should be done as a part of the estimation Process. Important thing is that they should be done to ensure the success of the Estimation Process and the Software Project as a whole
a) Create a detailed Work Break Down Structure. This directly impacts the accuracy of the estimate. This is one of the most important steps. The Work Break down structure should include any and all tasks that are within the scope of the Project, which is being estimated. The most serious handicap is the inability to clearly visualize the steps involved in the Project. Executing a Software Project is not just coding.
b) The work Break down structure will include the size and complexity of each software module that can be expressed as number of Lines of Code, Function Points, or any other unit of measure
c) The Work Break down structure should include tasks other than coding such as Software Configuration Management, various levels and types of Testing, Documentation, Communication, User Interaction, Implementation, Knowledge Transition, Support tasks(if any) and so on
d) Clearly indicate or eliminate any gray areas (vague/unclear specifications etc.)
e) Also take into account the various Risk Factors and down times. There are many different Risk Factors involved – Technical aspects such as availability of the Environment, Server/Machine uptime, 3rd party Software Hardware failures or Human aspects – Employee Attrition, Sick time, etc. Some of them may seem to be ‘overkill’ but real world experience shows that these factors affect the time lines of a project. If ignored they may adversely impact the Project timelines and estimates.
2) Estimate the effort in person-hours.
The Result of various tasks involved in step 1 is an effort estimate in person hours. The effort of various Project tasks expressed in person-hours is also influenced by various factors such as:
a) Experience/Capability of the Team members
b) Technical resources
c) Familiarity with the Development Tools and Technology Platform
3) Estimate the schedule in calendar months
The Project Planners work closely with the Technical Leads, Project Manager and other stakeholders and create a Project schedule. Tight Schedules may impact the Cost needed to develop the Application.
4) Estimate the project cost in dollars (or other currency)
Based on the above information the project effort is expressed in dollars or any other currency.
Measuring the Size/Complexity of the Software Program:
This is one of the most elusive aspects in the Software Cost Estimation Process.
There are different methodologies for arriving at and expressing the size/complexity of the Software Program. Some of the popular ones are
1) Function Points
2) Lines of Code
3) Feature Points
4) Mk II function points
5) 3D Function Points
6) Benchmarking
Each new software module to be developed can be categorized using the
a) Number of inputs
b) Number of outputs
c) Number of transactions
d) Algorithms
e) Features of the module
Based on the above factors the module can be categorized for example as Simple, Medium or Complex. If it is too Complex you could express it in multiples of the above three categories. The baseline effort in terms of person-hours it takes for each category is predefined based on historical data/metrics for a similar platform. This figure can be improvised/refined over a period of time this can be correlated to an algorithm for calculating Car Insurance Premium. This is used to estimate the size and the effort needed for Software Development.
posted by : dhamu
