To our families The formal language theory was born in the middle of our century as a tool for modelling and investigating the syntax of natural languages, and it has been developed mainly in connection with programming language handling. Of course, one cannot deny the impulses from neuronal net investigations, from logic, as well as the mathematical motivation of the early researches. The theory has rapidly become a mature one, with specific problems, techniques and results and with an internal self-motivated life. Abstract enough to deal with the essence of modelled phenomena, formal language theory has been applied during the last years to many further non-linguistical fields, sometimes surprisingly far from the previous areas of applications; such fields are developmental biology, economic modelling, semiotics of folklore, dramatic and musical works, cryptography, sociology, psychology, and so on. All these applications as well as the traditional ones to natural and programming languages revealed a rather common conclusion: very frequently, context-free gram mars, the most developed and the most "tractable" type of Chomsky grammars, are not sufficient. "The world is non-context-free" (and we shall "prove" this statement in Section 0.4). On the other hand, the context-sensitive grammars are too powerful and definitely "intractable" (many problems are undecidable or are still open; there is no semantic interpretation of the nonterminals an so on). This is the reason to look for intermediate generative devices, conjoining the simpli city and the beauty of context-free grammars with the power of context-sensitive ones.

This volume contains the texts of the tutorial lecture, five invited lectures and twenty short communications contributed for presentation at the Sixth International Meeting of Young Computer Scientists, IMYCS '90. The aim of these meetings is threefold: (1) to inform on newest trends, results, and problems in theoretical computer science and related fields through a tutorial and invited lectures delivered by internationally distinguished speakers, (2) to provide a possibility for beginners in scientific work to present and discuss their results, and (3) to create an adequate opportunity for establishing first professional relations among the participants.

The volume contains selected contributions from the scientific programme of the 5th International Meeting of Young Computer Scientists (IMYCS '88) held at Smolenice Castle (Czechoslovakia), November 14-18, 1988. It is divided into five chapters which approach the three crucial notions of contemporary theoretical computer science - machines, languages, and complexity - from different perspectives. The first chapter contains contributions dealing with problems of decidability, hierarchy, and complexity. Papers concerning different types and problems of automata theory form the second chapter. The contributions in the third chapter cover the large field of algorithmics from the study of program complexity to the domain of computational geometry. The two contributions of the fourth chapter are devoted to logic programming and inductive inference. The final chapter deals with problems of cryptography and contains the text of the IMYCS '88 tutorial on cryptography and data security delivered by A. Salomaa. The book will be a useful source for orientation in contemporary theoretical computer science and related fields such as software engineering and artificial intelligence for researchers and graduate students.

Logik ist eine wichtige Grundlage der Informatik. Sie ist fur die Formalisierung der Softwaretechnik, fur Verifikation und Spezifikation von Programmen und Datenbanken genauso erforderlich wie fur die logische Programmierung und die Kunstliche Intelligenz.
Dieses Buch entstand auf der Basis von Vorlesungen zur Logik, die der Autor seit Jahren fur Studierende der Informatik und informatiknaher Studiengange halt. Es gibt eine Einfuhrung in die Logik aus der Sicht der Informatik.

Der Tagungsband der 28. Jahrestagung der Gesellschaft fur Informatik gibt einen Uberblick uber diejenigen Trends in den Gebieten Bild- und Sprachverarbeitung, die fur die weitere Entwicklung der Informatik eine Schlusselrolle spielen. In den Beitragen werden Resultate der Spitzenforschung prasentiert, Anwendungen aus der Industrie formuliert und die gesellschaftliche Relevanz der betrachteten Themengebiete beleuchtet.