10-Software estimation

Key Software Metrics:

• Size is fundamental for software estimation including:
• Schedule (duration)
• Effort (cost)
• Quality (defects)
• Productivity
• Size (scope)

Estimation Challenges:

• Estimating code size is complex; requires progressive elaboration.
• Two types of sizes to estimate:
• Functional size (user-focused)
• Technical size (developer-focused)

Common Sizing Methods:

• T-shirt sizing (order of magnitude)
• Functional size (normalized to Function Points)
• Technical size (normalized to Implementation Units)

Cost Estimation:

• Personnel cost is the major factor in software development.
• Software size significantly dictates development staff costs.
• Staff-months are used for estimating effort; 100 staff-months means neither one developer working 100 months nor 100 developers working one month.

Agile Estimation Techniques:

• Experience-based techniques: Based on past project data.
• Algorithmic cost modeling: Mathematical function using attributes of product, project, and process.

COCOMO Models:

• Variants including Application Composition, Early Design, Reuse, and Post-architecture models help estimate effort based on varying project stages.

Use Case Points (UCP):

• UCP = (Weighted Actor Count + Weighted Use Case Count) * Technical Complexity Factor * Environmental Complexity Factor
• Factors influencing UCP include unique actors, use cases, and productivity.

Brooks’ Law and Communication:

• Additional staff on a late project increases delays due to training bottlenecks. Communication overhead increases complexity.

Effort and Calendar Time Estimation:

• COCOMO II provides formulas to convert effort (staff months) to calendar months.
• TDEV = 3 × Effort^(1/3) is a representative formula.

Caveats in Estimation:

• Accurate estimates hinge on experience, and UCP can be inflated without organization-specific adjustments.

Final Considerations:

• Understand the distinction between development cost and pricing, which is influenced by various external factors.