Process Algebra Research Articles

Formal analysis and verification of the PSTM architecture using CSP

Starting with the analysis of the source codes of the Python Software Transactional Memory (PSTM) architecture, this paper applies process algebra CSP to formally verify the architecture at a fine-grained level. We analyze the communication process and components of the architecture from multiple perspectives and establish models describing the communication behaviors of the PSTM architecture. We use model checker PAT to automatically simulate and verify the established model. After adapting the traditional transactional properties to the PSTM architecture, we analyze and verify five properties for the PSTM architecture, including deadlock freeness, atomicity, isolation, consistency and optimism. The verification results indicate that all the properties are valid. Based on the judgement of the execution logic of the communication procedure in the PSTM architecture, we can conclude that the architecture can have a proper communication and can guarantee atomicity, isolation, consistency and optimism. Besides, we also provide a case study with an application scenario and propose a corollary that the value of the shared counter is equal to the number of parallel processes. We verify whether the case study system can satisfy all the conditions of corollary from both positive and negative perspectives. The results show that the corollary is tenable.

Process calculi as a tool for studying coordination, contracts and session types

We recall techniques, mainly based on the theory of process calculi, that we used to prove results in twenty years of research, spanning across the old and the new millennium, on the expressiveness of coordination languages and on behavioural contracts for Service-Oriented Computing. Then, we show how such techniques recently contributed to the clarification of aspects that were unclear about session types, in particular, asynchronous session subtyping that was considered decidable since 2009, while it was proved to be undecidable in 2017.

An Information Ontology for the Process Algebra Model of Non-Relativistic Quantum Mechanics.

The process algebra model has been suggested as an alternative mathematical framework for non-relativistic quantum mechanics (NRQM). It appears to reproduce the wave functions of non-relativistic quantum mechanics to a high degree of accuracy. It posits a fundamental level of finite, discrete events upon which the usual entities of NRQM supervene. It has been suggested that the process algebra model provides a true completion of NRQM, free of divergences and paradoxes, with causally local information propagation, contextuality, and realism. Arguments in support of these claims have been mathematical. Missing has been an ontology of this fundamental level from which the formalism naturally emerges. In this paper, it is argued that information and information flow provides this ontology. Higher level constructs such as energy, momentum, mass, spacetime, are all emergent from this fundamental level.

IWSN: A novel method for modeling the interaction of web services

As the most notable implementation of service-oriented architectures, web services has brought some challenging research issues, one of which is the composition. Correct interaction among web services is the prerequisite of their successful composition. In this paper, we propose a novel approach to model dynamic interactive behavior of web services, aiming to effectively take advantage of the flexibility of service composition technology and guarantee the behavior compatibility of web services and further to facilitate the application of web service composition in healthcare field. An interaction model of web services based on Kahn process network (KPN) is presented in this paper, which is a data-flow and channel-based model supporting parallel and cooperative computation. Formal behavioral semantics of this model is defined by Pi-calculus process algebra and formal properties of the proposed model are discussed. An application case is demonstrated to illustrate how the proposed model can be applied to describe services behavior and their interaction. The reachability analysis of the application case is performed based on modal -calculus. How the supporting tool, i.e. CWB-NC, can be utilized to verify the properties we anticipate is presented.

Scalability and Performance Analysis in 5G Core Network Slicing

Slicing the 5G core network involves specifying network services according to the functional and quality requirements of typical 5G use cases. In doing so, assessing the scalability and performance of network services plays a leading role, since it allows dimensioning their capacity. Since years ago, diverse approaches have proposed formal models to analyze network services’ scalability, but they have not focused on the 5G core. Also, recent approaches have focused on analyzing network services’ performance in the 5G core, but they have not investigated the scalability issue. In this paper, we propose a method, based on the Performance Evaluation Process Algebra (PEPA), aiming at enabling the systematic analysis of the performance and scalability of network services in the 5G core. We introduce new composite structures based on PEPA and intended to model and evaluate 5G network core procedures. We illustrate how to use our method by presenting the modeling and assessment of two services regarding scalability and performance metrics. The former corresponds to the session establishment in a 5G network slice. The latter corresponds to the user registration process in a network slice for Vehicle-to-Everything. Results show the usefulness of our method to model 5G core network services and dimension the capacity of slices that implement them. Furthermore, the validation results corroborate, in terms of accuracy, that our PEPA-based method measures performance metrics (throughput, average response time, and processor utilization) with negligible difference regarding a traditional approach like the Layered Queuing Network model.

Formalization and Analysis of Haystack Architecture from Process Algebra Perspective

As a storage system architecture optimized for Facebook’s photo application, Haystack has four main advantages than before, including high throughput and low latency, fault-tolerance, cost-effectiveness and simplicity. With its widespread use, its validity and other major properties abstracted from the architecture need to be analyzed in a formal framework. However, to the best of our knowledge, there is nearly no research conducted to describe the communications and properties in Haystack. In this paper, we focus on the internal design of serving and uploading a photo of Haystack architecture and apply Communicating Sequential Processes (CSP) to formalize them in detail. By feeding the models into the model checker Process Analysis Toolkit (PAT), we have verified some crucial properties, including basic property and supplementary properties. Basic property contains Deadlock Freedom. Supplementary properties include synchronous concurrent access, asynchronous concurrent access, synchronous concurrent access with the same client, synchronous concurrent upload and synchronous concurrent upload with the same client. Finally, according to the verification results, we believe that from the CSP’s perspective, the properties of Haystack architecture is valid, which means that it meets the requirements of the documents of Facebook.

Even Simple π-Calculus Processes Are Difficult to Analyze

Mathematical models of distributed computations, based on calculus of mobile processes (π-calculus) are widely used for checking information security properties of cryptographic protocols. Since $$\pi $$-calculus is a Turing-complete computation model, this problem is unsolvable in the general case. Therefore, its study is carried out only for some special classes of π-calculus processes with restricted computational capabilities, for example, for nonrecursive processes with all runs limited in length, for processes with a limited number of parallel components, etc. However, even in these cases the proposed checking procedures are very time consuming. We assume that this is due to the very nature of the π-calculus processes. The goal of this paper is to show that even for the weakest passive adversary model and for relatively simple protocols that make use of only basic π-calculus operations, the checking of the information security properties of these protocols is a co-NP-complete problem.

Coupled similarity: the first 32 years

Coupled similarity is an equivalence on (labeled) transition systems; its distinguishing power lies between (weak) bisimilarity and (may) testing equivalence. Its main feature, compared to weak bisimilarity, is an additional $$\tau $$-law that abstracts from the atomicity of internal choices among several possible branches, thus allowing for gradual commitments. The need for this $$\tau $$-law in applications was motivated by van Glabbeek and Vaandrager in 1988. Parrow and Sjodin coined the term coupled simulation in 1992 as a coinductive proof technique for the comparison of distributed (not “just” concurrent) systems, heavily exploiting gradual commitments. Over the years, coupled similarity also gained significance for the definition and analysis of the correctness of encodings, of action refinement and contraction, and of branching-time semantics for various process calculi. In this paper, we compare variants and formalizations of coupled similarity and highlight its relevance.

A hybrid formal verification approach for QoS-aware multi-cloud service composition

Today, cloud providers represent their individual services with several functional and non-functional properties in various environments. Discovering and selecting an appropriate atomic service from a pool of activated services are a main challenge in the multi-cloud service composition. Minimizing the number of cloud providers is a critical matter in the service composition problem, which effects on energy consumption, response time and total cost. This paper presents a hybrid formal verification approach to assess the service composition in multi-cloud environments though the decreasing number of cloud providers to gain final service composition with a high level of Quality of Service (QoS). The presented approach provides behavioral modeling to examine the procedure of user’ requests, service selection, and composition in a multi-cloud environment. Also, the proposed approach permits analysis of the service composition using a Multi-Labeled Transition Systems (MLTS)-based model checking and Pi-Calculus-based process algebra methods for monitoring the functional specifications and non-functional properties as the QoS standards. In addition, the proposed approach satisfies the functional properties for the multi-cloud service composition. The experimental results proved the feasibility of the proposed approach with performance evaluations and some confirmation setups.

Static versus dynamic reversibility in CCS

The notion of reversible computing is attracting interest because of its applications in diverse fields, in particular the study of programming abstractions for fault tolerant systems. Most computational models are not naturally reversible since computation causes loss of information, and history information must be stored to enable reversibility. In the literature, two approaches to reverse the CCS process calculus exist, differing on how history information is kept. Reversible CCS (RCCS), proposed by Danos and Krivine, exploits dedicated stacks of memories attached to each thread. CCS with Keys (CCSK), proposed by Phillips and Ulidowski, makes CCS operators static so that computation does not cause information loss. In this paper we show that RCCS and CCSK are equivalent in terms of LTS isomorphism.

Modeling and verifying the topology discovery mechanism of OpenFlow controllers in software-defined networks using process algebra

• Formalizes a general framework for software-defined networks using CSP. • Instantiates and extends the framework to build a system model for TopoGuard. • Finds two loopholes of TopoGuard by verifying the system model in PAT. • Proposes a new topology discovery mechanism to solve the two loopholes. • Discusses the verification results for a larger set of networks. Software-Defined Networking (SDN) is an emerging paradigm, providing separation of concerns between controllers that manage the network and switches that forward data flow. SDN enables network programmability and reduces the complexity of network control and management. The OpenFlow protocol is a widely accepted interface between SDN controllers and switches. OpenFlow controllers are the core of Software-Defined Networks (SDNs). They collect topology information to build a global and shared view of the network, which is used to provide services for topology-dependent core modules and applications. Therefore, the accuracy of the centralized abstract view of the network is of outermost importance for many essential SDN operations. However, the topology discovery mechanism used in almost all the mainstream OpenFlow controllers suffers from two kinds of topology poisoning attacks: Link Fabrication Attack and Host Hijacking Attack. TopoGuard is a wide-spread secure OpenFlow controller, which improves the standard topology discovery mechanism, providing automatic and real-time detection of these two attacks. However, the mechanism of TopoGuard lacks formal verification, especially in the situation where some hosts are migrating to their new locations. In this paper, we propose a general parameterized framework, including the Communicating Sequential Processes (CSP) models of the network components and the interfaces among them. Two loopholes of TopoGuard are found by implementing and verifying the proposed system model, which is an instance of the framework, in the model checker Process Analysis Toolkit (PAT). Moreover, we propose a new topology discovery mechanism based on TopoGuard, which solves the two loopholes.

A calculus of concurrent graph-rewriting processes

State-of-the-art approaches to controlled graph rewriting focus on the specification of an external control layer over graph-rewriting rule applications and on the input-output semantics of the resulting systems, leading to a decreased relevance of many interesting operational aspects of graph transformation, as studied in the classical theory of algebraic graph rewriting.We propose a novel approach to controlled graph rewriting where we aim at bridging the gap between these two complementary approaches, defining an operational semantics for which classical concepts and results related to independence and parallelism of graph derivations can be recast.The calculus we propose is based on a control layer specified using (a fragment of) Milner's Calculus of Communicating Systems (CCS), where the actions specify the application of graph transformation rules to the current state, according to the Double-Pushout approach (DPO).In particular, we address the following aspects for our controlled graph-rewriting processes: (i) expressiveness of the control language, compared to a minimally complete reference language, Graph Programs, proposed by Habel and Plump; (ii) process equivalence based on labeled transition systems and a structural operational semantics; (iii) a unifying treatment of action independence, considering the corresponding notions from both process algebra and graph-rewriting theory; and (iv) parallelism and concurrency based on the notion of asynchronous (labeled) transition systems, obtained from an asynchronous version of the proposed calculus.

Towards Races in Linear Logic

Process calculi based in logic, such as $\pi$DILL and CP, provide a foundation for deadlock-free concurrent programming, but exclude non-determinism and races. HCP is a reformulation of CP which addresses a fundamental shortcoming: the fundamental operator for parallel composition from the $\pi$-calculus does not correspond to any rule of linear logic, and therefore not to any term construct in CP. We introduce non-deterministic HCP, which extends HCP with a novel account of non-determinism. Our approach draws on bounded linear logic to provide a strongly-typed account of standard process calculus expressions of non-determinism. We show that our extension is expressive enough to capture many uses of non-determinism in untyped calculi, such as non-deterministic choice, while preserving HCP's meta-theoretic properties, including deadlock freedom.

Typing Messages for Free in Security Protocols

Security properties of cryptographic protocols are typically expressed as reachability or equivalence properties. Secrecy and authentication are examples of reachability properties, while privacy properties such as untraceability, vote secrecy, or anonymity are generally expressed as behavioral equivalence in a process algebra that models security protocols. Our main contribution is to reduce the search space for attacks for reachability as well as equivalence properties. Specifically, we show that if there is an attack then there is one that is well-typed. Our result holds for a large class of typing systems, a family of equational theories that encompasses all standard primitives, and protocols without else branches. For many standard protocols, we deduce that it is sufficient to look for attacks that follow the format of the messages expected in an honest execution, therefore considerably reducing the search space.

Probabilistic Process Algebra to Unifying Quantum and Classical Computing in Closed Systems

We have unified quantum and classical computing in open quantum systems called qACP which is a quantum generalization of process algebra ACP. But, an axiomatization for quantum and classical processes with an assumption of closed quantum systems is still missing. For closed quantum systems, unitary operator, quantum measurement and quantum entanglement are three basic components for quantum computing. This leads to probability unavoidable. Along the solution of qACP to unify quantum and classical computing in open quantum systems, we unify quantum and classical computing with an assumption of closed systems under the framework of ACP-like probabilistic process algebra. This unification make it can be used widely in verification for quantum and classical computing mixed systems, such as most quantum communication protocols.

Probabilities in Session Types

This paper deals with the probabilistic behaviours of distributed systems described by a process calculus considering both probabilistic internal choices and nondeterministic external choices. For this calculus we define and study a typing system which extends the multiparty session types in order to deal also with probabilistic behaviours. The calculus and its typing system are motivated and illustrated by a running example.

Evaluation of Parallel System using Process Algebra

In this paper we discuss method for efficiency testing of a concurrent processes execution system. We use the concept of process algebra, it is an algebraic technique for the study of execution of parallel processes. Mathematical language is use for building models of computing system which make records about the execution of the procedure. We use PEPA tool, TAPA tool for making model. These tools provide formal explanation of computing system models. The execution related data about the system will be use to check the execution efficiency of the procedure. Here we use concept of markov chain analysis for execution of the concurrent processes.

A calculus for collective-adaptive systems and its behavioural theory

We propose a process calculus, named AbC, to study the behavioural theory of interactions in collective-adaptive systems by relying on attribute-based communication. An AbC system consists of a set of parallel components each of which is equipped with a set of attributes. Communication takes place in an implicit multicast fashion, and interaction among components is dynamically established by taking into account “connections” as determined by predicates over their attributes. The structural operational semantics of AbC is based on Labelled Transition Systems that are also used to define bisimilarity between components. Labelled bisimilarity is in full agreement with a barbed congruence, defined by relying on simple basic observables and context closure. The introduced equivalence is used to study the expressiveness of AbC in terms of encoding aspects of broadcast channel-based interactions and to establish formal relationships between system descriptions at different levels of abstraction.

Comparing Process Calculi Using Encodings

Encodings or the proof of their absence are the main way to compare process calculi. To analyse the quality of encodings and to rule out trivial or meaningless encodings, they are augmented with encodability criteria. There exists a bunch of different criteria and different variants of criteria in order to reason in different settings. This leads to incomparable results. Moreover, it is not always clear whether the criteria used to obtain a result in a particular setting do indeed fit to this setting. This paper provides a short survey on often used encodability criteria, general frameworks that try to provide a unified notion of the quality of an encoding, and methods to analyse and compare encodability criteria.

Semantic Structures for Spatially-Distributed Multi-Agent Systems

Spatial constraint systems (scs) are semantic structures for reasoning about spatial and epistemic information in concurrent systems. They have been used to reason about beliefs, lies, and group epistemic behaviour inspired by social networks. They have also been used for proving new results about modal logics and giving semantics to process calculi. In this paper we will discuss the theory and main results about scs.