Turku Centre for Computer Science

About: Turku Centre for Computer Science is a facility organization based out in Turku, Finland. It is known for research contribution in the topics: Decidability & Word (group theory). The organization has 382 authors who have published 1027 publications receiving 19560 citations.

A Model for Business Value in Large-Scale Agile and Lean Software Development

Abstract: As agile and lean methods continue to increase in popularity and move away from their home ground – small, co-located teams with an actively involved customer – they are faced with new challenges. One such challenge is the definition and communication of business value in large settings, where multiple development teams interact with multiple business stakeholders. This challenge is exacerbated by the fact that the term business value in agile contexts is not clearly defined, even though the creation of business value is one of the central themes in agile and lean development. In this paper, we propose a model for business value that is intended to make explicit different factors that constitute the concept of business value in agile and lean software development. This model has been jointly developed with industrial partners in the Cloud Software Finland research project. We aim to further evaluate and develop the model in the future within this research project.

On winning shifts of marked uniform substitutions

Abstract: The second author introduced with I. Torma a two-player word-building game [ Fund. Inform. 132 (2014) 131–152]. The game has a predetermined (possibly finite) choice sequence α 1 , α 2 , … of integers such that on round n the player A chooses a subset S n of size α n of some fixed finite alphabet and the player B picks a letter from the set S n . The outcome is determined by whether the word obtained by concatenating the letters B picked lies in a prescribed target set X (a win for player A ) or not (a win for player B ). Typically, we consider X to be a subshift. The winning shift W ( X ) of a subshift X is defined as the set of choice sequences for which A has a winning strategy when the target set is the language of X . The winning shift W ( X ) mirrors some properties of X . For instance, W ( X ) and X have the same entropy. Virtually nothing is known about the structure of the winning shifts of subshifts common in combinatorics on words. In this paper, we study the winning shifts of subshifts generated by marked uniform substitutions, and show that these winning shifts, viewed as subshifts, also have a substitutive structure. Particularly, we give an explicit description of the winning shift for the generalized Thue–Morse substitutions. It is known that W ( X ) and X have the same factor complexity. As an example application, we exploit this connection to give a simple derivation of the first difference and factor complexity functions of subshifts generated by marked substitutions. We describe these functions in particular detail for the generalized Thue–Morse substitutions.

Subword Balance in BinaryWords, Languages and Sequences

Abstract: We investigate binary words and languages having a balanced structure of (scattered) subwords. We introduce a "difference function" D for binary words. For D=0, the resulting language is properly context-sensitive. Parikh matrices constitute a useful technical tool in the study, we investigate also the independence of their entries. The investigation is extended to concern ω-words and periodicity. For the Fibonacci word, the D-values are in many ways connected with the Fibonacci numbers.

Determining directional distances between points and shorelines using sweep line technique

Abstract: Distances from points to closest shorelines in a given direction are used, for example, in some models for estimating wave exposure. Such distances, also called fetch lengths, can be determined using standard geographic information systems. However, performance may be a problem if these distances are required for a great number of study points. Two new algorithms for determining fetch lengths for study points in the same directions are presented in this paper. It is assumed that the two-dimensional map is stored in vector format, i.e. shorelines of islands and mainland are stored as polygons. The first algorithm works on a set of undirected line segments derived from the shoreline polygons. The other works on a raster representation of the map. The algorithm saves memory by postponing the rasterisation until necessary. Both of the new algorithms have superior efficiency to a previously reported algorithm when the number of study points is large.

Refining Reactive Systems in HOL Using Action Systems

Abstract: Work on embedding reasoning about programs in a mechanised logic has mostly focused on meta-theoretic reasoning about programming logics or notations This paper describes an attempt to formalise a theory of actions systems in HOL, in such a way that a tool for developing and reasoning about distributed and reactive systems can be built on top of the theory By reducing action system refinement proofs to proofs of data refinement between sequential statements, we are able to reuse existing theories and tools for sequential programs