Defensive Design

Defensive Design

1. Defensive design is the practice of anticipating every possible way that an end-user could misuse a system or device.

   • For example: During the defensive design process, methods are put in place to eliminate misuse.
     • You can tell when the defensive design hasn't been good enough.
       • For example: The program crashes, the program behaves in an unintended fashion or data security has been compromised

2. The first thing that is always being decided is what kind of interface to code for.

   • There is a fine balancing act with giving the user access to all the information and abilities that they might need, while at the same time imposing limits on the things that they commonly get wrong.
     • Examples of interfaces are: menu-driven user interfaces, television/remote control interfaces and public booths with a touch sensitive screen.
       • On a remote control interface, the only actions that the user can perform is to use the up-down-left-right buttons on their remote control to navigate and a 'select' button to select an option.

3. Screen Widgets and User Interface Widgets

   • A hard coded menu has difficulty of going wrong. However, it does require a certain level of flexibility
     • A 'graphical widget' is a small self-contained object that allows the user to select some data.
       • The calendar widget pops up and tells you the date
       • The colour picker widget allows the user to pick any colour they want so they can use it in their work.
       • The drop down lists and spinners present to the user, the amount of data selections they can save.

4. Good Instructions and repeat entry

   • An example of a repeat entry would be entering a password and getting it wrong so you would have to keep trying to get it right
     • Text entry is the most flexible way of accepting inputs from the user, but also the most problematic. Users can mistype, or enter data into the wrong field, or simply input gibberish.
       • Password entries often ask for the password to be re-entered so they can check that what they entered is what they intended to answer

5. The Input Box. This is basically the form that is filled out online when you apply for something. It normally asks you for your name, age, address and email.

   • As the user is now free to try and enter whatever they like. The program handling the input needs to include some defensive measures. This is sometimes known as validation
     • There are 4 validation method and they are: checking and limiting the length of the data, checking the range of the data, checking the type of the data and checking the format of the data.