Styles of computing
Peter B. Andersen
Department of Information and Media Studies
The Wiener Building, Room 224.
IT City Katrinebjerg
Aarhus University, Helsingforsgade 14
DK-8200 Aarhus N, Denmark
Abstract
The paper defines a style of building technical systems called activity-based design. The main idea is to build technical systems from the following two simple rules
Sign --> Invisible + Visible
Invisible Sign --> Sign*
A system is considered a sign with an invisible and a visible component. The latter is the user interface while the former can contain zero or more components that are themselves signs. The basic template of design is the activity: a set of actions and operations subsumed under at shared goal. To each action is associated a set of thematic roles and to the activity as a whole is associated a set of macro-roles. The components of the technical system are designed to participate in the actions of the activity in a certain thematic role: Agent, Theme, Instrument, Location, Source, Destination, etc. Since in principle all components are signs with a user interface, automatic components and humans can change place. It is in principle possible to shift between manual and automatic operation for all parts of the activity. It is claimed that such systems are understandable and easy to handle in error situations:
Understandable: Since a human can operate component A, he can use his experience from using it in his own activity to understand the way component B uses A as Instrument in its activity. In addition, since thematic roles form the basic data-structure and since linking rules exist that convert thematic role structures into sentences, the system is so to speak self-describing.
Easy to handle in error situations: since all components in principle have a user interface, it is always possible to reconfigure it by switching off the more complicated automatic systems, and handle errors manually.