Software Architecture: Meta and SOLID Principles in C# — Lesson 3: Liskov Substitution and Interface Segregation

Learning Objectives

• Evaluate inheritance and substitution behavior against client expectations
• Apply ISP to design focused contracts for different consumers
• Detect fragile hierarchies, fat interfaces, invalid assumptions, and testing gaps

Guided Demonstration

1. Review the requirement, environment, dependencies, roles, risks, and expected result.
2. Demonstrate the relevant configuration, development, analysis, migration, security, or support workflow.
3. Capture settings, outputs, logs, screenshots, code, reports, or test evidence.
4. Compare the observed result with the acceptance criteria and identify gaps.

Hands-On Activity

Redesign an inheritance and interface model and verify substitutability with tests.

• Document assumptions and the planned sequence before making changes.
• Complete the activity and preserve evidence of normal and exception behavior.
• Record issues, corrective actions, and reusable operational or development notes.

Scenario Analysis

• Identify business, user, data, security, compliance, and operational impacts.
• Compare alternative decisions and explain the selected approach.
• Define ownership, communication, rollback, support, and improvement actions.

Troubleshooting Focus

• Separate symptoms from causes and collect evidence before applying a fix.
• Check configuration, permissions, data, dependencies, capacity, connectivity, and recent changes.
• Validate service restoration, user experience, and prevention measures.

Validation Checklist

• The requirement and expected result are clear.
• The selected configuration, design, code, query, migration, or process is documented.
• Normal, boundary, failure, security, compliance, and operational conditions are reviewed.
• The result is supported by evidence and the next improvement is prioritized.

Lesson Outcome

Learners can explain and apply Liskov Substitution and Interface Segregation in a realistic scenario and support the result with documented evidence.