This volume presents a selection of papers presented at the 3rd European Workshop on Appl ications and Theory of Petri Nets that took place in Villa Monastero, Varenna (Italy) in the period September 27 - September 30, 1982. The I ist of topics included: nets and related models, mathematical analysis of nets, transformations and morphisms of nets, formal languages and nets, parallel program verification and nets, the pro blem of time in nets, programming languages based on nets, applications to distributed systems, applications to realtime systems, software ~~gineering, hardware design and its implementation, recoverability problems, nets and formal semantics; net tools. The diversity of topics on this list witnesses the fact that the researchers from very different areas presented their contributions and discussed various research problems during the workshop. This interaction of scientists looking at the area of Petri nets from very different points of view makes this series of workshops interesting and worthwi le. The volume documents the progress of the research concerning Petri nets during a one year time from the 2nd European Workshop held in Bad Honnef in 1981. We think that this was a substantial progress indeed. This observation is even more pleasant if one real izes that during the workshop in Varenna we have celebrated 20 years of "existence" of Petri nets (the seminal work by prof. C.A. Petri appeared precisely 20 years ago). We are very proud to present an invited address by prof. C.A. Petri in this volume.

This book contains the reports of selected projects involving natural language commu nication with pictorial information systems. More than just a record of research results, however, it presents concrete applications to the solution of a wide variety of problems. The authors are all prominent figures in the field whose authoritative contributions help ensure its continued expansion in both size and significance. Y. C. Lee and K S. Fu (Purdue University, USA) survey picture query languages which form an interface between the pictorial database system and the user and support infor mation retrieval, data entry and manipulation, data analysis and output generation. They include explicit picture query languages that augment alphanumeric data query langua ges as well as languages and command sets which are implicitly embedded in a pictorial information system but perform similar functions. It is worth mentioning that some forms of query languages can be transformed from a given set of natural language senten ces by using ATN (Augmented Transition Networks), which consequently allows for na turallanguage communication with information system.