Defensive Design Considerations (OCR GCSE Computer Science)

What is defensive design?

• Defensive design is an approach to software development where every possible input from a user is considered
• This is done to anticipate all of the ways a user could misuse a program
• Defensive design ensures that the final program is robust and reliable for all users
• Occasionally, some errors can occur in software that can not be foreseen by the developer when writing the software

How can a software developer anticipate errors in programs?

• Many errors can occur in a program and some of these can be difficult to anticipate when initially developing the software
• The programmer must ensure the software has a way of dealing with the potential errors to ensure their software does not crash
• Some examples of these errors include
  
  • Peripheral errors
  • Disk errors
  • Communication errors
• In these instances, a programmer must ensure their software deals with these errors to ensure it is robust and reliable for its users

Peripheral errors

• Peripherals commonly don't perform as intended, such as printers and this can cause an issue for the end user
• If a printer runs out of paper, runs out of ink or has a paper jam; the user should have the option of reprinting their document
• These considerations must be pre-planned in the software

Disk errors

• Programs such as word processing software must be able to account for errors on a disk drive
• Example errors that may occur on a disk include
  • Disk running out of space
  • Files and folders not being found
  • Corrupted files
• These issues must be preplanned in the software the user has an alternative option, for example, saving their work on another disk

Communication errors

• Applications which use online systems must be connected to a host server
• When a connection is lost, the program should provide a way for the user to cancel their request and try again
• The program may also be able to automatically retry if the connection resumes

What is Authentication?

• Authentication is the process of ensuring that a system is secure by asking the user to complete tasks to prove they are an authorised user of the system
• Authentication is done because bots can submit data in online forms
• Authentication can be done in several ways, these include
  • Usernames and Passwords
  • CAPTCHA
• Other methods that programmers can do to authenticate the user is include
  • Allowing users to recover passwords via email links and SMS codes
  • Encrypting data