Computing, despite the relative brevity of its history, has already evolved into a subject in which a fairly large number of subdisciplines can be identified. Moreover, there has been a noticeable tendency for the different branches of the subject each to develop its own intellectual culture, tradition and momentum. This is not, of course, to suggest that any individ- ual subdiscipline has become a watertight compartment or that developments in one branch of the subject have tended to take place in total isolation from developments in other related areas. Nevertheless, it does mean that a...