Defensive Design

Defensive design or defensive programming is a practice followed by programmers. Its aim is to ensure software works under unforeseen circumstances and invalid inputs, enhancing overall reliability and usability.

Principles of Defensive Design

Validation: Check input for correctness and only proceed when the input meets a set of predefined rules. This helps in preventing errors and retaining a sense of control.
Prevention of Errors: Implementing checks or constraints for data inputs can avoid invalid or unexpected inputs, reducing chances of errors.
Feedback: Provide clear messages for users when things are working correctly, and when they are not. Effective feedback can help users correct their inputs if needed.
Fail-Safe: In situations when things go wrong, a system should fail quietly and safely. A technique often used is exception handling which ensures that program execution continues even after an error occurs.
Simplicity: Minimise the complexity of systems. Simple designs are often easier to test, maintain and operate.
Automation: Use automation to take human error out of the equation where possible. This can include automatic calculations, data backups, and scheduled tasks or updates.

Benefits of Defensive Design

Improved Usability: Defensive design helps in enhancing user experience. The use of error messages and feedback provides a more interactive system.
Reduce Maintenance Cost: Through preventing the occurrence of errors, the cost and time spent in modifying or correcting the software decreases.
Reliability: By considering potential errors and designing safeguards against them, the resulting system is more reliable.
Longevity: Defensive design extends the life of a system by making it more robust and able to handle a variety of situations.

Remember, defensive design is an essential practice in creating robust, user-friendly, and reliable software programmes. It aids in error prevention, correction, and guidance, making systems more efficient.