The IBM Vienna Laboratory has made a significant contribution to the work on the semantic description of computer systems. Both the operational semantics descriptions ("VDL") and the later work on denotational semantics ("Meta-IV", "VEM") contain interesting scientific ideas. Partly because of the large scale of the applications tackled, much of the material is difficult to access.

Hans Bekic was one of the key members of the "Vienna Lab". His tragic death in a mountain accident in October 1982 left unpublished an important body of research. (The editorial notes below contain further details of his scientific career; a biographical note has been written by Professors Kulch and Zemanek).

Hans' computer research can be considered under three headings. His work on programming languages took place partly within IPIP WG 2.1 of which he was a member from 1965-1971. He also had an influence on the development of PVI. Hans was a mathematician and so moved naturally to research on formal language description. Most of his scientific career was spent on this work. Hans was largely responsible for the move by the Vienna Lab from operational to denotational semantics. He was a member of IPIP WG 2.2 from 1969 until his death. Work on the description of parallelism occupied the last years of Hans' life. This was a difficult period in whicSi the laboratory was employed on practical programing tasks: Hans pursued his scientific work in his "spare time".

This book contains a selection of Hans Bekic's papers. Publication of his specific contribution presents special problems. Much of hie work was unpublished and even, in some cases, existed only as hand written manuscripts. Sometimes Hans postponed publication because he considered a piece of work to be flawed» in other cases - it must be conceded - his habit of leaving things to the last minute resulted in his missing a deadline for publication. In spite of this, Hans' work has been widely circulated and has influenced others. His untimely death means that he cannot complete the work in the way he would have wished.

After discussions with his family, friends and colleagues, it was decided that it would be valuable to publish a selection of Hans' papers. To alleviate any fear that he would not have wished them to be published in this form, his own reservations - where known - have been included. A list of all known writings and main talks on computer topics is given below (book reviews etc. are not listed)» the most important papers are reproduced.