CSC/ECE 517 Fall 2007/wiki2 9 kk

Principle of Least Astonishment

The principle of least astonishment states that when you are presented with a different outcomes one should always pick the one of least ambiguity or suprise. The principle has applications in a lot of fields. This wiki serves as a guide for the reader to understand more about this principle. The principle of least astonishment goes by different names depending on the field of application like element of least suprise, Occam's Razor etc.

Examples

The simplest example is in programming where the name of a function does not indicate its functionality.

int add(int a, int b)
{
   return (a*a+b*b);
}

The function above is supposed to add two numbers but actualy returns the sum of squares of the two numbers which would suprise the programmer who is using the function. Applying the principle of least astonishment, we can either rename the function to indicate its functionality or we can rewrite the functionality itself to correspond to its name.

int sum_of_squares(int a, int b)
{
   return (a*a+b*b);
}

int add(int a, int b)
{
   return a+b
}

Application in Programming

User interface design

The principle of least astonishment is used a lot in user interface design. Joel Spolsky has an article introducing user interface design using the principle of least astonishment. The article looks at a lot of examples of using the element of least suprise by comparing user interface design in Windows and Macintoshes.

A more general introduction to the application of the principle of least astonishment to UI design can be found here.

API Design

The principle of least astonishment also plays an important role in API or library design. For example, when designing libraries or API's we want meaningful function names which does what the function name implies. A very basic introduction and some examples can be found here. Steven's Tech Talk has a very good introduction to proper API design using the principle of least astonishment.

Webpage Design

Webpage design like UI design also finds the application of the principle of least astonishment. IBM has an excellent article on how this can be done.

General Software Design

DDJ has an article which introduces the user to applying the principle of least suprise to general software design by using an example of arrays in language called APL.

Applications in Other Fields

The principle also finds a lot of applications in other fields though it might be called by a different name.