Connectedness and synchronization

Contracts as games on event structures

Model-checking games for fixpoint logics with partial order models

We give an event structures based true-concurrency characterization of deep inference proofs. The method is general to all deep inference systems that can be expressed as term rewriting systems. This delivers three consequences in a spectrum from theoretical to practical: the event structure characterization i provides a qualification of proof identity akini¾?to proof nets for multiplicative linear logic and to atomic flows for classical logic; ii provides a concurrency theoretic interpretation for applications in logic programming; iii reduces the length of the proofs, and thereby extends the margin of proof search applications.

We analyse the reduction of differential interaction nets from the point of view of so-called ‘true concurrency,’ that is, employing a non-interleaving model of parallelism. More precisely, we associate with each differential interaction net an event structure describing its reduction. We show how differential interaction nets are only able to generate confusion-free event structures, and we argue that this is a serious limitation in terms of the concurrent behaviours they may express. In fact, confusion is an extremely elementary phenomenon in concurrency (for example, it already appears in CCS with just prefixing and parallel composition) and we show how its presence is preserved by any encoding respecting the degree of distribution and the reduction semantics. We thus infer that no reasonably expressive process calculus may be satisfactorily encoded in differential interaction nets. We conclude with an analysis of one such encoding proposed by Ehrhard and Laurent, and argue that it does not contradict our claims, but rather supports them.

We review the conceptual development of (true) concurrency and branching time starting from Petri nets and proceeding via Mazurkiewicz traces, pomsets, bisimulation, and event structures up to higher dimensional automata (HDAs), whose acyclic case may be identified with triadic event structures and triadic Chu spaces. Acyclic HDAs may be understood as extending the two truth values of Boolean logic with a third value .

The paper consists of two parts. In the first, an analytical algebra AFPi of finite nondeterministic concurrent processes is introduced. The semantics of processes specified by a formula of AFPi is characterized by a set of partial orders with "non-actions". The notion of process equivalence is introduced and its complete axiomatization is proposed.The "descriptive" algebra AFPo for specifying structure of finite (acyclic) Petri nets is presented. The interrelation between AFPo and AFPi is investigated.Key wordsconcurrent nondeterministic processestrue concurrencypartially ordered setsnon-actionsdenotational semanticsPetri netsoccurrence netsA-netsM-density

Mining frequent partial orders from a collection of sequences was introduced as an alternative to mining frequent sequential patterns in order to provide a more compact/understandable representation. The motivation was that a single partial order can represent the same ordering information between items in the collection as a set of sequential patterns (set of totally ordered sets of items). However, in practice, a discovered set of frequent partial orders is still too large for an effective usage. We address this problem by proposing a method for ranking partial orders with respect to significance that extends our previous work on ranking sequential patterns. In experiments, conducted on a collection of visits to a website of a multinational technology and consulting firm we show the applicability of our framework to discover partial orders of frequently visited webpages that can be actionable in optimizing effectiveness of web-based marketing.

Event structures are a well-established model in concurrency theory.Two structurally dierent methods of associating transition system semantics to event-oriented models are distinguished in the literature.One of them is based on congurations (event sets), the other on residuals (model fragments).In this paper, we deal with a highly expressive model of event structures event structures for resolvable conict (RC-structures) and provide isomorphism results on these two types of transition systems constructed from RC-structures, in step and partial order semantics.

We provide a model-checking technique for a logic for true concurrency, whose formulae predicate about events in computations and their causal dependencies. The logic, that represents the logical counterpart of history-preserving bisimilarity, is naturally interpreted over event structures. It includes minimal and maximal fixpoint operators and thus it can express properties of infinite computations. Global algorithms are not convenient in this setting, since the event structure associated with a system is typically infinite (even if the system is finite state), a fact that makes also the decidability of model-checking non-trivial. Focusing on the alternation free fragment of the logic, along the lines of some classical work for the modal mu-calculus, we propose a local model-checking algorithm. The algorithm is given in the form of a tableau system, for which, over a class of event structures satisfying a suitable regularity condition, we prove termination, soundness and completeness.

Many interesting problems in numerical optimization are hybrid optimal control problems. Hybrid optimal control (HOC) problems include both continuous-valued variables and categorical variables in the problem formulation. For the types of problems envisioned here the categorical variables will specify the structure or sequence of events that qualitatively describes the trajectory or mission. Continuous variables are used in the modeling of the continuous dynamics. In this work, the mission planning problem is of interest. The problem is qualitatively different from the typical interception of multiple targets as the discrete variables now represent events like impulses, coast and thrust arcs that change the structure of the problem. In addition, the number of events in the categorical sequence is not fixed. For the dynamical assembly of events required for the solution of the mission planning problem, a scheme that defines events as modules consisting of parameters and constraints is presented. The method assembles the respective events one next to the other in time according to the given mission structure. For the generation of the initial guess, two new methods were developed that approximate optimal low-thrust trajectories. The first method, based on genetic algorithms (GA), handles the rendezvous constraints explicitly using a conditional penalty function. The second method, feasible region analysis (FRA), is based on GA and nonlinear programming (NLP), which allows taking advantage of the GA capabilities in finding a global optimum and NLP ability in handling constraints. A rendezvous problem with known solution is solved.

String-equivalence, Behaviour-equivalence, Observation-equivalence, Exhibited-Behaviour-equivalence, Failure-equivalence and Testing equivalence are re-defined and discussed on Petri Net models of concurrent systems. Since the previous notions, being based on sequences of events, do not distinguish real concurrency from its sequential non-deterministic simulation, they are refined, in order to capture the concurrency degree of the systems, in terms of the subset languages approach. The equivalence notions introduced are then compared w.r.t. their strength.

The Euclidean distance construction of order homomorphisms

Long-tract gene conversions (LTGC) can result from the repair of collapsed replication forks, and several mechanisms have been proposed to explain how the repair process produces this outcome. We studied LTGC events produced from repair collapsed forks at yeast fragile site FS2. Our analysis included chromosome sizing by contour-clamped homogeneous electric field electrophoresis, next-generation whole-genome sequencing, and Sanger sequencing across repair event junctions. We compared the sequence and structure of LTGC events in our cells to the expected qualities of LTGC events generated by proposed mechanisms. Our evidence indicates that some LTGC events arise from half-crossover during BIR, some LTGC events arise from gap repair, and some LTGC events can be explained by either gap repair or “late” template switch during BIR. Also based on our data, we propose that models of collapsed replication forks be revised to show not a one-end double-strand break (DSB), but rather a two-end DSB in which the ends are separated in time and subject to gap repair.

Proving correctness of concurrent systems is quite difficult because of the high level of nondeterminism, especially in large and complex ones. AMC is a model checking system for verifying asynchronous concurrent systems by using branching time temporal logic. This paper introduces the techniques of the modelling approach, especially how to construct models for large concurrent systems with the concept of hierarchy, which has been proved to be effective and practical in verifying large systems without a large growth of cost.

The aim of this paper is to present graphical version of Brouwer’s fixed point theorem and to establish some useful results of partial order set and nonexpansive mapping defined on a partial order set. One application of the fixed point theory by combining graph theory is discussed here by using Dijkstra’s algorithms which is useful in computer science.