This very special, 2^7.0 – 1 volume of Fundamenta Informaticae is dedicated to Andrzej Skowron on the occasion of his 70^th birthday. The contributions are on an invitational basis, but they have been reviewed according to the usual standards of the journal. The editors want to thank all the contributors and reviewers for their great work. Without it, this volume would be much less special.

It is very hard, if even possible, to describe Andrzej Skowron in a finite collection of words. He is such an unique personality and scientist. To get some understanding what he is like it may help to read the accounts included in this preface. These accounts are provided by persons who interact with Andrzej for years on both professional and personal grounds: Roman Świniarski with family, Janusz Kacprzyk, Damian Niwiński, and Stanisław Matwin.

When we started to circulate the idea of this special volume among Andrzej's extended scientific family, we have met an enthusiastic response. So enthusiastic in fact, that we were initially a little bit overwhelmed. Everybody wanted to be on board. We managed to convince several groups of researchers to join forces and write one comprehensive, yet compact article instead of several. In this way, it was possible to fit the material in one, thirty-six-piece volume.

The thirty-six articles that make this special volume of Fundamenta Informaticae span over a very wide range of topics. They reflect Andrzej Skowron's activities as a researcher and a scholar as well as his influence on a broad scientific community. In order to make this volume more approachable we have ordered the papers with respect to general areas their represent. To do that we have used a methodology that has quite bit to do with results of one of the research projects Andrzej was recently involved in. Namely, we have manually performed a semantic clustering of our contribution pool. As a result the papers have been organized into four disjoint clusters (thematic groups) that we briefly introduce below.

First of the clusters gathers articles that correspond to some fundamental directions in recent and past research of Andrzej Skowron. The reader will find in this cluster papers representing such areas as: foundations of rough sets, logical aspects of both rough and related models of computation, foundational issues relating to logical aspects of non-classical computational systems, formal and computational aspects of inference systems, and nature-inspired computational systems. In this cluster we have contributions by: Mihir K. Chakraborty and Mohua Banerjee; Anna Gomolińska and Marcin Wolski; Ewa Orłowska and Ivo Düntsch; Yiyu Yao; Lech Polkowski and Maria Semeniuk-Polkowska; Ludwik Czaja; Grzegorz Rozenberg, Gheorghe Paun, and Mario J. Perez-Jimenez; Alberto Pettorossi, Fabio Fioravanti, Maurizio Proietti, and Valerio Senni; Andrzej Szałas and Patrick Doherty.

The second cluster contains papers that describe research results in topics associated with discovering, representing and making use of knowledge learned form data. In particular, several of approaches described in these papers make use of reducts and decision rules. The contributions made by Andrzej Skowron to methods and algorithms for representation, reduction, and simplification of information retrieved from data are instrumental here. There are also papers that deal with approximations and approximation spaces, an area pioneered by Andrzej. Members of this cluster are papers by: Mikhail Moshkov, Talha Amin, Igor Chikalov, and Beata Zielosko; Roman Słowiński, Salvatore Greco, and Izabela Szczęch; Jerzy Grzymała-Busse and Patrick G. Clark; Wojciech Ziarko and Xugunag Chen; Shusaku Tsumoto and Shoji Hirano; Zbigniew Raś and Hakim Touati; Hui Wang and Ivo Düntsch; Zbigniew Suraj and Krzysztof Pancerz; Jan Komorowski, Marcin Kruczyk, Nicholas Baltzer, Jakub Mieczkowski, Michał Dramiński, and Jacek Koronacki.

The third group of contributions relates to another large area of research on which Andrzej Skowron left his mark. The papers represent studies on fundamentals and applications of granular approach to knowledge-based systems as well as investigations into underlying notions of closeness, similarity, and nearness. They also address challenges associated with construction and usage of granular systems – in particular multi-layered, hierarchical ones – in knowledge discovery and decision support. Papers by the following authors make this group: Sankar K. Pal, Jayanta Kumar Pal, and Shubhra Sankar Ray; Marzena Kryszkiewicz; Bożena Kostek and Andrzej Kaczmarek; Alicja Wakulicz-Deja, Agnieszka Nowak-Brzezińska, and Małgorzata Przybyła-Kasperek; James Peters and Sheela Ramanna; Hung Son Nguyen, Sinh Hoa Nguyen, Tuan Trung Nguyen, and Marcin Szczuka; Guoyin Wang, Yuchao Liu, Deyi Li, and Wen He; Witold Pedrycz; Tsau Young Lin, Yong Liu, and Wenliang Huang.

The fourth and final group contains nine papers that represent a little wider range of topics. Among them are papers that deal with data processing in general, including research related to database technology as well as search techniques. There are papers in this cluster that deal with data and knowledge representation and navigation. There are also described various aspects of data mining including those that make use of multiagent approach as well as methods based on processing of visual information. In this cluster the reader will find contributions by: Jarosław Stepaniuk, Maciej Kopczyński, and Tomasz Grzes; Dominik Ślęzak, Piotr Synak, Arkadiusz Wojna, and Jakub Wróblewski; Henryk Rybiński and Jacek Lewandowski; Jiming Liu, Hao Lan Zhang, and Yanchun Zhang; Jan G. Bazan, Andrzej Jankowski, and Sylwia Buregwa-Czuma; Wojciech Froelich, Rafał Deja, and Grażyna Deja; Piotr Wasilewski and Adam Krasuski; Ning Zhong, Linchan Qin, Shengfu Lu, and Mi Li; Andrzej Czyżewski and Karol Lisowski.

The editors of this special volume would like to wish a Happy Birthday to Andrzej and hope that he will like this little gift.

Dominik Ślęzak

Hung Son Nguyen

Marcin Szczuka

October 2013