Refinement-based Technique Research Articles

A Multi-level Refinement Approach for Structural Synthesis of Optimal Probabilistic Models

Probabilistic models play an important role in many fields such as distributed systems and simulations. Like non-probabilistic systems, they can be synthesized using classical refinement-based techniques, but they also require identifying the probability distributions to be used and their parameters. Since a fully automated and blind refinement is generally undecidable, many works tried to synthesize them by looking for the parameters of the distributions. Syntax-guided synthesizing approaches are more powerful, they try to synthesize models structurally by using context-free grammars. However, many problems arise like huge search space, the complexity of generated models, and the limitation of context-free grammars to define constraints over the structure. In this paper, we propose a multi-step refinement approach, based on meta-models, offering several abstraction levels to reduce the size of the search space. More specifically, each refinement step is divided into two stages in which the desired shape of models is first described by context-sensitive constraints. In the second stage, model templates are instantiated by using global optimization techniques. We use our approach to a synthesize a set of optimal probabilistic models and show that context-sensitive constraints coupled with the multi-level abilities of the approach make the synthesis task more effective.

Revisiting snapshot algorithms by refinement-based techniques

The snapshot problem addresses a collection of important algorithmic issues related to distributed computations, which are used for debugging or recovering distributed programs. Among existing solutions, Chandy and Lamport have proposed a simple distributed algorithm. In this paper, we explore the correct-byconstruction process to formalize the snapshot algorithms in distributed system. The formalization process is based on a modeling language Event B, which supports a refinement-based incremental development using RODIN platform. These refinement-based techniques help to derive correct distributed algorithms. Moreover, we demonstrate how other distributed algorithms can be revisited. A consequence is to provide a fully mechanized proof of the resulting distributed algorithms.

Refinement-based formal verification with heterogeneous timing

In this paper we propose a refinement-based technique to formally verify data transfer in a heterogeneous timing framework. Novel data transfer models are proposed to represent data communication between two locally independent clock domains via an asynchronous handshake environment. As a case study, we apply our technique to automatically verify data transfer in a previously published architecture for globally asynchronous locally synchronous on-chip systems. In this case study, we find several race conditions, hazards, and other dangers that were not mentioned in the original publication, and we find additional delay constraints that avoid some of the detected dangers.