Mechanized Theory of Event Structures: A Case of Parallel Register Machine

The true concurrency models, and in particular event structures, have been introduced in the 1980s as an alternative to operational interleaving semantics of concurrency, and nowadays they are regaining popularity. Event structures represent the causal dependency and conflict between the individual atomic actions of the system directly. This property leads to a more compact and concise representation of semantics. In this work-in-progress report, we present a theory of event structures mechanized in the COQ proof assistant and demonstrate how it can be applied to define certified executable semantics of a simple parallel register machine with shared memory.

Reachability Analysis of Asynchronous Dynamic Pushdown Networks Based on Tree Semantics Approach

<em>ADPN (Asynchronous Dynamic Pushdown Networks) are an abstract model for concurrent programs with recursive procedures and dynamic thread creation. Usually, asynchronous dynamic pushdown networks are described with interleaving semantics, in which the backward analysis is not effective. In order to improve interleaving semantics, tree semantics approach was introduced. This paper extends the tree semantics to ADPN. Because the reachability problem of ADPN is also undecidable, we address the context-bounded reachability problem and provide an algorithm for backward reachability analysis with tree-based semantics Approach.</em>

True Concurrency Semantics

The model checking algorithms have been widely studied for timed automata, it's a validation technique for automatically verifying correctness properties of finite-state systems, which are based on interleaving semantics. Therefore the actions are assumed instantaneous. To overcome the hypothesis of temporal and structural atomicity of actions, we use the durational actions timed automata model (daTA). This model is based on the maximality semantics. Properties to be verified are expressed using the Timed Computation Tree Logic (TCTL). For dealing with formal verification, the Maximality-based Region Graph (MRG) is defined and an adaptation of the model checking algorithm is proposed. The use of the maximality semantics based verification provides new class of properties related to simultaneous progress of actions at different states.

REWRITING LOGIC-BASED SEMANTICS OF P SYSTEMS AND THE MAXIMAL CONCURRENCY

We use distributed labeled transition systems and their modal logics in order to compare the concurrency degrees of the P systems and their encoding as rewrite theories in rewriting logic. We show that the maximal concurrency given by the maximal parallel rewriting semantics of the P systems can be expressed in rewriting logic only by interleaving semantics. The maximal concurrency of the membrane interactions is only partially captured.

TERMINATING ALTERNATOR

In this paper, we present an program that enables the transformation of a non-terminating alternator into a terminating alternator. Our solution is stabilization preserving and has the potential to preserve maximal concurrency (if available) provided by the non-terminating alternator. It can also be used to transform a program that is stabilizing in interleaving semantics into a program that is stabilizing in powerset semantics. We also discuss how the terminating alternator can be used to enable a process to gain an understanding of system stability.