Selected Decision Problems for Square-Refinement Collage Grammars -- Weighted Tree Automata over Valuation Monoids and Their Characterization by Weighted Logics -- Partial Conway and Iteration Semiring-Semimodule Pairs -- Kleene Theorem in Partial Conway Theories with Applications -- Rational Transformations and a Kleene Theorem for Power Series over Rational Monoids -- Equational Weighted Tree Transformations with Discounting -- Quantum Automata Theory - A Review -- Graph Automata: The Algebraic Properties of Abelian Relational Graphoids -- A Survey on Picture-Walking Automata -- Identity Problems, Solvability of Equations and Unification in Varieties of Semigroups Related to Varieties of Groups -- Algebraic Systems and Pushdown Automata -- Where Automatic Structures Benefit from Weighted Automata -- Survey:Weighted Extended Top-Down Tree Transducers Part III - Composition -- Valuations of Weighted Automata: Doing It in a Rational Way -- Selected Combinatorial Properties of Random Intersection Graphs. Weighted Tree Automata over Valuation Monoids and Their Characterization by Weighted Logics -- Partial Conway and Iteration Semiring-Semimodule Pairs -- Kleene Theorem in Partial Conway Theories with Applications -- Rational Transformations and a Kleene Theorem for Power Series over Rational Monoids -- Equational Weighted Tree Transformations with Discounting -- Quantum Automata Theory - A Review -- Graph Automata: The Algebraic Properties of Abelian Relational Graphoids -- A Survey on Picture-Walking Automata -- Identity Problems, Solvability of Equations and Unification in Varieties of Semigroups Related toVarieties of Groups -- Algebraic Systems and Pushdown Automata -- Where Automatic Structures Benefit from Weighted Automata -- Survey: Weighted Extended Top-Down Tree Transducers Part III - Composition -- Valuations of Weighted Automata: Doing It in a Rational Way -- Selected Combinatorial Properties of Random Intersection Graphs.

This Festschrift volume is published in honor of Symeon Bozapalidis on the occasion of his retirement after more than 35 years of teaching. The topics covered are: weighted automata over words and trees, tree transducers, quantum automata, graphs, pictures and varieties of semigroups. Since 1982 -- at the Aristotle University of Thessaloniki -- Symeon's main interests have been closely connected with the algebraic foundations in computer science. In particular, he contributed to the development of the theory of tree languages and series, the axiomatization of graphs, picture theory, and fuzzy languages. The volume, which focuses on the research interests of Symeon, contains 15 thoroughly refereed invited papers, written by his colleagues, friends, and students. Most of the papers were presented at the Workshop on Algebraic Foundations in Computer Science, held in Thessaloniki, Greece, during November 7--8, 2011.