Abstract

‘External memories’ raise a question about context: ‘external to what?’ External memory is a technical term applied to everything that can be memorized in an individual's environment. As a general rule I have decided to retain the technical terms that characterize the area of the topic under discussion. It was Ted Nelson who coined the word hypertext in 1967 to signify non-sequential writing as well as a computer technology that allowed the user to move about freely by means of software links. I shall use the term software to mean computer programs. Electronic publishing started with the Xanadu system developed by Nelson. At the lowest level a hypertext is a system for managing databases that allows the user to connect together information screens using links. It is a collection of texts interconnected by means of interactive switches. This dynamic presentation of non-linear texts could not be printed on a conventional page. Hypertext allows the origin of a piece of information to be traced. In this article traceability is synonymous with explanation: ‘Why was this equipment designed in one way rather than another?’ It is about discovering the route of the design process that led to the eventual idea for the equipment. The necessary explanations are often required long after decisions were made, and this is why traceability is a matter of memory. The term agent is often used to mean those members of a community that act on its behalf. There are agents for a company or public department. There are biological agents. In a non-technological world traceability is ideally carried out by human agents who explain to other human agents. The term agent has been extended into the computer world to mean software to which the user delegates, sometimes unwittingly, tasks of varying complexity. These are then called software agents. In this article I refer to agent in its wider meaning, to be understood as an actor or an entity able to act in a limited context and having a quite specific role and appropriate resources.