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Software Cost Estimation Techniques

This document discusses several software cost estimation techniques: 1. Top-down and bottom-up approaches - Top-down estimates system-level costs while bottom-up estimates costs of each module and combines them. 2. Expert judgment - Widely used technique where experts estimate costs based on past similar projects. It utilizes experience but can be biased. 3. Delphi estimation - Estimators anonymously provide estimates in rounds to reach consensus without group dynamics influencing individuals. 4. Work breakdown structure - Hierarchical breakdown of either the product components or work activities to aid bottom-up estimation.

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SOFTWARE COST ESTIMATION TECHNIQUES Prepared by V.Santhi Assistant Professor Department of Computer Applications Bon Secours College for Women Thanjavur
 Software cost estimation based on past performance  Historical data used to identify cost factor Methods 1. Top-down 2. Bottom-up Top-Down:  Focuses on system level costs  Computing resources & personnel to develop the system  Costs of Configuration management  Quality assurance  System Integration  Testing  Publications
Bottom –Up:  Estimates the cost to develop each module or subsystem.  Combine overall cost. Techniques: 1. Expert Judgment 2. Delphi Cost Estimation 3. Work Breakdown Structure 4. COCOMO Model
EXPERT JUDGMENT  Most widely used estimation technique  Top-down estimation technique Ex: Process Control System 10 months & $ 1 million cost New System  25% more activities  increase our time and cost  Same computer and external sensing/controlling devices & same people available to develop the new system  Reduce our estimate by 20%
Advantages:  Experience  Expert confident that the project is similar to previous one.  Group of experts prepare a consensus estimate.  Minimize individual oversights.
Disadvantages:  Interpersonal group dynamics may have on individuals in the group.  Political consideration  Dominance of an overly assertive group member.
DELPHI COST ESTIMATION  Developed by Rand Corporation in 1948  Without introducing the adverse side effects of group meetings 1. A coordinator provides each estimator with the System Definition document 2. Estimators study the definition and complete their estimate anonymously. Ask questions of the coordinator. 3. Coordinator prepares and distributes a summary of the estimators response
4. Estimators complete another estimate, again anonymously using the results from the previous estimate. 5. The process is iterated for as many rounds as required. No group discussion is allowed during the entire process
VARIATION OF DELPHI COST ESTIMATION 1. Coordinator provides each estimator with a system Definition and an estimation form 2. Coordinator calls a group meeting and discuss the estimation issues with each other. 3. Estimators complete their estimates anonymously 4. The coordinator prepares a summary of estimates, but does not record any rationale. 5. The coordinator calls a group meeting to focus on issues where the estimation vary widely 6. Estimators complete another estimate, again anonymously. The process repeated so many
WORK BREAKDOWN STRUCTURE  Bottom-up estimation  Hierarchical chart  individual parts of the system  WBS  product hierarchy / process hierarchy Product Hierarchy  Identifies the product components and how its interconnected. Process Hierarchy  Identifies the work activities and the relationship among those activities.
PRODUCT WBS
PROCESS WBS