This is the English translation of Kaljulaid's 1979 Tartu/Minsk Candidate thesis, which originally was typewritten in Russian and manufactured in not so many copies. The thesis was devoted to representation theory in the spirit of his thesis advisor B. I. Plotkin: representations of semigroups and algebras, especially extension to this situation, and application of the notion of triangular product of representations for groups introduced by Plotkin. Through representation theory, Kaljulaid became also interested in automata theory, which at a later phase became his main area of interest. Another field of research concerns combinatorics. Besides being an outstanding and most dedicated mathematician Uno Kaljulaid was also very much interested in the history of mathematics. Kaljulaid was also very interested in the teaching and exposition, or popularization of mathematics. There is a whole series of papers about algebraic matters, culminating in a brilliant, elementary - although partly rather philosophical - essay devoted to Galois theory. Another such series is his excellent essay of Diophantine Geometry in various installments, followed by his eloge to another of his teachers Yu. I. Manin. We believe that the inclusion of these papers here will make it more interesting for beginners, and perhaps even contribute to attracting young people to mathematics.

Constraint programming is like an octopus spreading its tentacles into databases, operations research, artificial intelligence, and many other areas. The concept of constraint programming was introduced in artificial intelligence and graphics in the 1960s and 1970s. Now the related techniques are used and studied in many fields of computing. Different aspects of constraint processing are investigated in theoretical computer science, logic programming, knowledge representation, operations research, and related application domains. Constraint programming has been included in the lists of related topics of many conferences. Nevertheless, only in 1993 were the first forums held, devoted as a whole to this field of knowledge. These were the First Workshop on Principles and Practice of Constraint Programming (PPCP'93) which was held in Newport, Rhode Island, USA, April 28-30, the International Workshop on Constraint Processing (at CSAM'93) held in St. Petersburg, Russia, July 20-21, and the NATO Advanced Study Institute (NATO AS ) on Constraint Programming held in Parnu, Estonia, August 13-24. NATO A Sis are aimed to be schools bringing together leading researchers and practitioners from industry and academia in some area of knowledge to provide a concise picture of the work done and results obtained by different groups. This is intended for dissemination of advanced knowledge not yet taught regularly in of new topics university. However, ASis must also encourage the introduction into university curricula as well as foster international scientific contacts.

The 9th East-European Conference on Advances in Databases and Information Systems was held on September 12-15, 2005, in Tallinn, Estonia. It was organized in a cooperation between the Institute of Cybernetics at Tallinn University of Technology, the Department of Computer Engineering of Tallinn University of Technology, and the Moscow chapter of ACM SIGMOD. The main objective of the ADBIS series of conferences is to provide a - rum for the disseminationof excellent researchaccomplishmentsand to promote interaction and collaboration between the Database and Information Systems research communities from Central and East European countries and the rest of the world. The ADBIS conferences provide an international platform for the presentationofresearchondatabasetheory, thedevelopmentofadvancedDBMS technologies, and their advanced applications in particular in information s- tems. The 2005 conference continued the ADBIS conferences held in St. Pete- burg (1997), Poznan (1998), Maribor (1999), Prague (2000), Vilnius (2001), Bratislava (2002), Dresden (2003), and Budapest (2004). The conference c- sisted of regular sessions with technical contributions reviewed and selected by an international Program Committee, as well as of invited talks and tutorials given by leading scientists. For the ?rst time the ADBIS conferences had a satellite event, a workshop on data mining and knowledge discovery. The ADMKD 2005 workshop, with its own international ProgramCommittee as well as proceedings, servedas a forum toencourageresearchersandpractitionerstodiscussandinvestigatedatamining research and implementation issues, and to share experience in developing and deploying data mining system

This volume constitutes the proceedings of the 6th International Symposium on Programming Language Implementation and Logic Programming (PLILP '94), held in Madrid, Spain in September 1994. The volume contains 27 full research papers selected from 67 submissions as well as abstracts of full versions of 3 invited talks by renowned researchers and abstracts of 11 system demonstrations and poster presentations. Among the topics covered are parallelism and concurrency; implementation techniques; partial evaluation, synthesis, and language issues; constraint programming; meta-programming and program transformation; functional-logic programming; and program analysis and abstract interpretation.

This volume contains the proceedings of the Fifth International Symposium onProgramming Language Implementation and Logic Programming (PLILP '93), held in Tallinn, Estonia, in August 1993. The series of PLILP symposiums was established to promote contacts and information exchange among scientists who share common interests in declarative programming techniques, logic programming, and programming languages imnplementation. Researchers from the fields of algorithmic programming languages as well as logic, functional, object-oriented, and constraint programming constitute the audience of PLILP. The volume contains three invited talks and 24 selected contributed papers grouped intoparts on: integration of different paradigms, constraint programming, staticanalysis and abstract interpretation, grammars, narrowing, parallelism, and implementation techniques. The volume closes with six abstracts of systems demonstrations and posters.

This book constitutes the refereed proceedings of the 14th International Baltic Conference on Databases and Information Systems, DB&IS 2020, held in Tallinn, Estonia, in June 2020.* The 22 revised papers presented were carefully reviewed and selected from 52 submissions. The papers are centered around topics like architectures and quality of information systems, artificial intelligence in information systems, data and knowledge engineering, enterprise and information systems engineering, security of information systems. *The conference was held virtully due to the COVID-19 pandemic.