Personal Notice Board

Imagine a personal notice board virtual service that you can configure to display useful information. All kinds of things could potentially be displayed: the temperature forecast for the day, to help you choose suitable clothing; particularly important appointments scheduled for that day that you might want time to prepare for; reminders that particular foods are in short supply and need replenishing; the latest football results; a reminder that your mobile phone needs charging when your it is broadcasting a notification that it has less than a third of its battery power left; current travel advisories that are relevant to your trip to work, or an alert that your teenager hasn't yet returned from the party she went to the previous evening.

You want certain information on weekdays, while other information is only relevant on weekends. Perhaps you want your notice board to be displayed on your bedside radio in the morning, or maybe you'd prefer that your notice board is read to you by the speech synthesizer in your car while you drive to work on weekdays (as long as you aren't listening to the radio, in which case it would be intrusive), but printed out in time for breakfast at the weekend. If you use the display in the kitchen then you may need to specify how the limited real estate on the screen should be shared among your family members, and which items should only be displayed in more private spaces.

What underlies the configuration of virtual services such as a personal notice board is a collection of rules, each one specifying that certain things should happen when a particular set of conditions hold; we refer to such rules as policies