arXiv subjects

Christophe Gaston

Publications and source records attributed to Christophe Gaston.

8 recordsLinked to original sources

arXiv2025

Runtime Verification of Interactions Using Automata

Runtime verification consists in observing and collecting the execution traces of a system and checking them against a specification, with the objective of raising an error when a trace does not satisfy the specification. We consider distributed systems consisting of subsystems which communicate by message-passing. Local execution traces consisting of send and receive events are collected on each subsystem. We do not assume that the subsystems have a shared global clock, which would allow a reordering of the local traces. Instead, we manipulate multitraces, which are collections of local traces. We use interaction models as specifications: they describe communication scenarios between multiple components, and thus specify a desired global behaviour. We propose two procedures to decide whether a multitrace satisfies an interaction, based on automata-theoretic techniques. The first procedure is straightforward, while the second provides more information on the type of error and integrates the idea of reusability: because many multitraces are compared against one interaction, some preprocessing can be done once at the beginning. We implement both procedures and compare them.

cs.LO↗

arXiv2024

Efficient Interaction-Based Offline Runtime Verification of Distributed Systems with Lifeline Removal

Runtime Verification (RV) refers to a family of techniques in which system executions are observed and confronted to formal specifications, with the aim of identifying faults. In Offline RV, observation is done in a first step and verification in a second, on a static artifact collected during observation. In this paper, we define an approach to offline RV of Distributed Systems (DS) against interactions. Interactions are formal models describing communications within a DS. DS are composed of subsystems deployed on different machines and interacting via message passing. Therefore, observing executions of a DS entails logging a collection of local execution traces, one for each subsystem, that we call a multi-trace. A major challenge in analyzing multi-traces is that there are no practical means to synchronize the ends of observations of all local traces. We address this via an operation, called lifeline removal, which we apply on-the-fly on the specification during verification once a local trace has been entirely analyzed. This operation removes from the interaction the specification of actions occurring on the subsystem that is no-longer observed. This may allow further execution of the specification via removing deadlocks due to the partial orders of actions. We prove the correctness of the resulting RV algorithm and introduce two optimization techniques which we also prove correct. We implement a Partial Order Reduction (POR) technique via the selection of a one-unambiguous action (as a unique first step to a linearization) which existence is determined via another use of the lifeline removal operator. Additionally, Local Analyses (LOC) i.e., the verification of local traces, can be leveraged during the global multi-trace analysis to prove failure more quickly. Experiments illustrate the application of our RV approach and the benefits of our optimizations.

cs.FL↗

arXiv2024

Tooling Offline Runtime Verification against Interaction Models : recognizing sliced behaviors using parameterized simulation

Offline runtime verification involves the static analysis of executions of a system against a specification. For distributed systems, it is generally not possible to characterize executions in the form of global traces, given the absence of a global clock. To account for this, we model executions as collections of local traces called multi-traces, with one local trace per group of co-localized actors that share a common clock. Due to the difficulty of synchronizing the start and end of the recordings of local traces, events may be missing at their beginning or end. Considering such partially observed multi-traces is challenging for runtime verification. To that end, we propose an algorithm that verifies the conformity of such traces against formal specifications called Interactions (akin to Message Sequence Charts). It relies on parameterized simulation to reconstitute unobserved behaviors.

cs.SE↗

arXiv2023

A Term-based Approach for Generating Finite Automata from Interaction Diagrams

Non-deterministic Finite Automata (NFA) represent regular languages concisely, increasing their appeal for applications such as word recognition. This paper proposes a new approach to generate NFA from an interaction language such as UML Sequence Diagrams or Message Sequence Charts. Via an operational semantics, we generate a NFA from a set of interactions reachable using the associated execution relation. In addition, by applying simplifications on reachable interactions to merge them, it is possible to obtain reduced NFA without relying on costly NFA reduction techniques. Experimental results regarding NFA generation and their application in trace analysis are also presented.

cs.FL↗

arXiv2022

Dealing with observability in interaction-based Offline Runtime Verification of Distributed Systems

Interactions are formal models describing asynchronous communications within a Distributed System (DS). They can be drawn in the fashion of sequence diagrams and executed thanks to an operational semantics akin to that of process algebras. Executions of DS can be characterized by tuples of local traces (one per subsystem) called multi-traces. For a given execution, those local traces can be collected via monitoring and the resulting multi-trace can be analysed using offline Runtime Verification (RV). To that end, interactions may serve as formal references. In practice, however, not all subsystems may be observed and, without synchronising the end of monitoring on different subsystems, some events may not be observed, e.g. the reception of a message may be observed but not the corresponding emission. So as to be able to consider all such cases of partial observation, we propose an offline RV algorithm which uses removal operations to restrict the reference interaction on-the-fly, disregarding the parts concerning no longer observed subsystems. We prove the correctness of the algorithm and assess the performance of an implementation.

cs.LO↗

arXiv2021

A structural operational semantics for interactions with a look at loops

Message Sequence Charts & Sequence Diagrams are graphical models that represent the behavior of distributed and concurrent systems via the scheduling of discrete and local emission and reception events. We propose an Interaction Language (IL) to formalize such models, defined as a term algebra which includes strict and weak sequencing, alternative and parallel composition and four kinds of loops. This IL is equipped with a denotational-style semantics associating a set of traces (sequences of observed events) to each interaction. We then define a structural operational semantics in the style of process algebras and formally prove the equivalence of both semantics.

cs.FL↗

arXiv2020

A small-step approach to multi-trace checking against interactions

Interaction models describe the exchange of messages between the different components of distributed systems. We have previously defined a small-step operational semantics for interaction models. The paper extends this work by presenting an approach for checking the validity of multi-traces against interaction models. A multi-trace is a collection of traces (sequences of emissions and receptions), each representing a local view of the same global execution of the distributed system. We have formally proven our approach, studied its complexity, and implemented it in a prototype tool. Finally, we discuss some observability issues when testing distributed systems via the analysis of multi-traces.

cs.LO↗

arXiv2020

Revisiting Semantics of Interactions for Trace Validity Analysis

Interaction languages such as MSC are often associated with formal semantics by means of translations into distinct behavioral formalisms such as automatas or Petri nets. In contrast to translational approaches we propose an operational approach. Its principle is to identify which elementary communication actions can be immediately executed, and then to compute, for every such action, a new interaction representing the possible continuations to its execution. We also define an algorithm for checking the validity of execution traces (i.e. whether or not they belong to an interaction's semantics). Algorithms for semantic computation and trace validity are analyzed by means of experiments.

cs.SE↗