Software Project Effort Estimation

Question 1

Cost/Schedule Expert Judgement Technique

Answer 1

• One or more experts in both software development and the application domain use their experience to predict softwre costs.
• Process iterates until some consensus is reached
• Typically over-optimistic
• Estiamte = (Pessimistic + Optimistic + 4*MostLikely)/6
• Advantage = Relatively cheap estimation method. Can be accurate if experts have substantial experience of similar systems.
• Disadvantage = Very inaccurate if there are no experts!

Question 2

Cost/Schedule Bottom-Up Estimation

Answer 2

• Start at the lowest system level.
• The cost/schedule of each component is estimated. All these costs are added to produce a final cost estimate.
• Advantage = Can be accurate, if the system has been designed in detail
• Disadvantage = May underestiamte cost of system level activities such as integration and documentaion

Question 3

Cost/Schedule Top-Down Estimation

Answer 3

• A cost/schedule estimate is established by considering the overall functionality of the product and how that functionality is provided by interacting sub-functions.
• Cost estimates are made on the absis of the logical function rather than the components implementing that function
• Advantage = takes into account costs such as integration, configuration management and documentation
• Disadvantage = Can underestimate the cost of solving difficult low-level technical problems.

Question 4

Cost/Schedule Pricing-to-Win Estimation

Answer 4

• The software cost/schedule is estimated to be whatever the customer has available to spend on the project.
• The estiamted effort depends on the customer’s budget and not on the software functionality
• Advantage = Good chances to get the contract
• Disadvantages = The probability that the customer gets the system he or she wants is small. Costs do not accurately reflect the work required.

Question 5

Cost/Schedule Parkinson’s Law Estimation

Answer 5

• Parkinson’s Law states that work expands to fill the time available
• This means that the cost is determined by available resources rather than by objective assessment.
  
  • Ex. If the software has to be delivered in 12 months and 5 people are available, the effort required is estiamted to be 60 person-months.
• Advantage = No overspending
• Disadvantage = System is usually unfinished

Question 6

Cost/Schedule Estimation by Analogy

Answer 6

• Applicable when other projects in the same application domain have been completed.
• The cost of a new project is computed by comparing the project to a similar completed project in the same application domain
• Advantages = accurate if the project data available
• Disadvantages = Impossible if no comparable project has been tackled. needs systematically maintained project databes (Expensive)

Question 7

Case Based Reasoning (CBR)

Answer 7

• Involved matching the current problem against ones that have already been encountered in the past and reworking the solutions of the past problems in the current context.
• Can be represented as a cyclical process that is divided into 4 following sub processes:
  
  • Retrieve the most similar case or cases from the case base
  • Reuse the case to solve the problem
  • Revise the proposed solution if necessary
  • Retain the solution for future problem solving.

Question 8

Empirical Factor Models (EFP)

Answer 8

• Provide direct estiamtes of effort.
• Based on:
  
  • Primary cost factor such as size
  • A number of secondary adjustment factors or cost drivers
• Cost drivers are characteristics of the project, process, products or resoruces that influence effort.
• Cost drivers are used to adjust the preliminary estimate provided by the primary cost factor.