Rules

Letting users define rules (using plain English) can be an effective way of providing advanced functionality. Well-articulated rules can help "tell the story" of the desired system behavior. Rules typically define a condition that must be met and then what happens when the condition is met.

Most email applications allow users to define rules to manage incoming email. In the case of Outlook 2007, the rule is described as a sentence and users edit the rule by clicking on the hyperlinks within the sentence (click to see image full-size):

Excel uses rules for conditional formatting. Here the rule is presented using standard GUI controls:

Gmail provides great feedback in its "create a filter" function. In the first step, defining the condition that must be met, users have the option to "test the search":

In the next step, defining what happens when the condition is met, the system automatically runs the search, so users can see exactly which messages will be subject to the behavior they define: