The Committee Decision Problem

We introduce the (b,n)-Committee Decision Problem (CD) - a generalization of the consensus problem. While set agreement generalizes consensus in terms of the number of decisions allowed, the CD problem generalizes consensus in the sense of considering many instances of consensus and requiring a processor to decide in at least one instance. In more detail, in the CD problem each one of a set of n processes has a (possibly distinct) value to propose to each one of a set of b consensus problems, which we call committees. Yet a process has to such that all processes deciding for the same committee decide the same value. We study the CD problem in the context of a wait-free distributed system and analyze it using a combination of distributed algorithmic and topological techniques, introducing a novel reduction technique. We use the reduction technique to obtain the following results. We show that the (2,3)-CD problem is equivalent to the musical benches problem of Gafni and Rajsbaum (DISC 2005), and both are equivalent to (2,3)-set agreement, closing an open question left there. Thus, all three problems are wait-free unsolvable in a read/write shared memory system, and they are all solvable if the system is enriched with objects capable of solving (2,3)-set agreement. While the previous proof of the impossibility of musical benches was based on the Borsuk-Ulam (BU) Theorem, it now relies on Sperner's Lemma, opening intriguing questions about the relation between BU and distributed computing tasks. // Ce rapport présente un problème de prise de décisionsmultiples (qui généralise le problème du consensus) et étudie sa calculabilité (à l'aide de techniques de réductions)

An Introduction to the Topological Theory of Distributed Computing with Safe-consensus

AbstractThe theory of distributed computing shares a deep and fascinating connection with combinatorial and algebraic topology. One of the key ideas that facilitates the development of the topological theory of distributed computing is the use of iterated shared memory models. In such a model processes communicate through a sequence of shared objects. Processes access the sequence of objects, one-by-one, in the same order and asynchronously. Each process accesses each shared object only once. In the most basic form of an iterated model, any number of processes can crash, and the shared objects are snapshot objects. A process can write a value to such an object, and gets back a snapshot of its contents.The purpose of this paper is to give an introduction to this research area, using an iterated model based on the safe-consensus task (Afek, Gafni and Lieber, DISCʼ09). In a safe-consensus task, the validity condition of consensus is weakened as follows. If the first process to invoke an object solving a safe-consensus task returns before any other process invokes it, then the process gets back its own input; otherwise the value returned by the task can be arbitrary. As with consensus, the agreement requirement is that always the same value is returned to all processes.A safe-consensus-based iterated model is described in detail. It is explained how its runs can be described with simplicial complexes. The usefulness of the iterated memory model for the topological theory of distributed computing is exhibited by presenting some new results (with very clean and well structured proofs) about the solvability of the (n,k)-set agreement task. Throughout the paper, the main ideas are explained with figures and intuitive examples

Warsaw as a center of music tourism

The article describes music tourism, i.e. a subset of cultural tourism. The aim of the present paper is to present the elements of Warsaw’s cultural offering, land management and identity, which underlie the potential for the development of music tourism in the capital city of Poland. The author assumed that Warsaw’s music tourism resources make Poland’s capital city a center of music tourism. The aim set forth the author accomplished through fieldwork observation and in-depth interviews with the Promotion Office of the Cultural Department of the Municipality of Warsaw

A review on DISC 2005, the 19th International Symposium on Distributed Computing

DISC is an international symposium on the theory, design, analysis, implementation and application of distributed systems and networks. The well-known International Symposium on Distributed Computing is organized annually in cooperation with the European Association for Theoretical Computer Science (EATCS). This is a review on the 19th International Symposium on Distributed Computing, which took place in Kraków, Poland, on September 26--29, 2005. The proceedings of DISC 2005 are published by Springer, as volume 3724 of the Lecture Notes in Computer Science (LNCS) series. The conference website can be found at www.mimuw.edu.pl/~disc2005.Postprint (published version

The Universe of Symmetry Breaking Tasks

Processes in a concurrent system need to coordinate using a shared memory or a message-passing subsystem in order to solve agreement tasks such as, for example, consensus or set agreement. However, often coordination is needed to “break the symmetry” of processes that are initially in the same state, for example, to get exclusive access to a shared resource, to get distinct names or to elect a leader. This paper introduces and studies the family of generalized symmetry breaking (GSB) tasks, that includes election, renaming and many other symmetry breaking tasks. Differently from agreement tasks, a GSB task is “inputless”, in the sense that processes do not propose values; the task specifies only the symmetry breaking requirement, independently of the system's initial state (where processes differ only on their identifiers). Among many various characterizing the family of GSB tasks, it is shown that (non adaptive) perfect renaming is universal for all GSB tasks

Business Courts and Interstate Competition

Over the past two decades, specialized trial courts that hear business disputes primarily or exclusively have been established in nineteen states. To explain the recent surge of interest in these courts, policymakers and scholars alike have cited the process of interstate competition. Specifically, these commentators have argued that business courts serve, among other purposes, to attract out-of-state companies to expand their business, reincorporate, or litigate disputes in the jurisdiction that created the business court. This Article critically evaluates each of these theories. It argues first that business courts do not serve to attract companies from other states because business expansion decisions in the United States are rarely driven by the high quality of the courts in a particular jurisdiction. It next argues that business courts are unlikely to attract incorporation business because their core attributes are such that they are unlikely to compete successfully with the Delaware Court of Chancery. The Article goes on to argue that while the creation of a business court may in some cases serve to divert litigation business to local lawyers, the opportunities for diversion are relatively limited. The Article then draws upon these insights to offer a number of suggestions as to how future business courts should be designed. It suggests that states seeking to attract technology companies should think twice before creating a business and technology court. It notes that major institutional reforms will be required if states wish to use business courts to attract incorporation business away from Delaware. It also identifies additional steps that states might take to more effectively attract litigation business. The Article concludes by evaluating the viability of several non-competition-based rationales for establishing business courts