Treo: Textual Syntax for Reo Connectors

Reo is an interaction-centric model of concurrency for compositional specification of communication and coordination protocols. Formal verification tools exist to ensure correctness and compliance of protocols specified in Reo, which can readily be (re)used in different applications, or composed into more complex protocols. Recent benchmarks show that compiling such high-level Reo specifications produces executable code that can compete with or even beat the performance of hand-crafted programs written in languages such as C or Java using conventional concurrency constructs. The original declarative graphical syntax of Reo does not support intuitive constructs for parameter passing, iteration, recursion, or conditional specification. This shortcoming hinders Reo's uptake in large-scale practical applications. Although a number of Reo-inspired syntax alternatives have appeared in the past, none of them follows the primary design principles of Reo: a) declarative specification; b) all channel types and their sorts are user-defined; and c) channels compose via shared nodes. In this paper, we offer a textual syntax for Reo that respects these principles and supports flexible parameter passing, iteration, recursion, and conditional specification. In on-going work, we use this textual syntax to compile Reo into target languages such as Java, Promela, and Maude.Comment: In Proceedings MeTRiD 2018, arXiv:1806.0933

A Procedure for Splitting Processes and its Application to Coordination

We present a procedure for splitting processes in a process algebra with multi-actions (a subset of the specification language mCRL2). This splitting procedure cuts a process into two processes along a set of actions A: roughly, one of these processes contains no actions from A, while the other process contains only actions from A. We state and prove a theorem asserting that the parallel composition of these two processes equals the original process under appropriate synchronization. We apply our splitting procedure to the process algebraic semantics of the coordination language Reo: using this procedure and its related theorem, we formally establish the soundness of splitting Reo connectors along the boundaries of their (a)synchronous regions in implementations of Reo. Such splitting can significantly improve the performance of connectors.Comment: In Proceedings FOCLASA 2012, arXiv:1208.432

Relating BIP and Reo

Coordination languages simplify design and development of concurrent systems. Particularly, exogenous coordination languages, like BIP and Reo, enable system designers to express the interactions among components in a system explicitly. In this paper we establish a formal relation between BI(P) (i.e., BIP without the priority layer) and Reo, by defining transformations between their semantic models. We show that these transformations preserve all properties expressible in a common semantics. This formal relation comprises the basis for a solid comparison and consolidation of the fundamental coordination concepts behind these two languages. Moreover, this basis offers translations that enable users of either language to benefit from the toolchains of the other.Comment: In Proceedings ICE 2015, arXiv:1508.0459

A Compositional Semantics for Stochastic Reo Connectors

In this paper we present a compositional semantics for the channel-based coordination language Reo which enables the analysis of quality of service (QoS) properties of service compositions. For this purpose, we annotate Reo channels with stochastic delay rates and explicitly model data-arrival rates at the boundary of a connector, to capture its interaction with the services that comprise its environment. We propose Stochastic Reo automata as an extension of Reo automata, in order to compositionally derive a QoS-aware semantics for Reo. We further present a translation of Stochastic Reo automata to Continuous-Time Markov Chains (CTMCs). This translation enables us to use third-party CTMC verification tools to do an end-to-end performance analysis of service compositions.Comment: In Proceedings FOCLASA 2010, arXiv:1007.499

Toward Sequentializing Overparallelized Protocol Code

In our ongoing work, we use constraint automata to compile protocol specifications expressed as Reo connectors into efficient executable code, e.g., in C. We have by now studied this automata based compilation approach rather well, and have devised effective solutions to some of its problems. Because our approach is based on constraint automata, the approach, its problems, and our solutions are in fact useful and relevant well beyond the specific case of compiling Reo. In this short paper, we identify and analyze two such rather unexpected problems.Comment: In Proceedings ICE 2014, arXiv:1410.701

Handshaking Protocol for Distributed Implementation of Reo

Reo, an exogenous channel-based coordination language, is a model for service coordination wherein services communicate through connectors formed by joining binary communication channels. In order to establish transactional communication among services as prescribed by connector semantics, distributed ports exchange handshaking messages signalling which parties are ready to provide or consume data. In this paper, we present a formal implementation model for distributed Reo with communication delays and outline ideas for its proof of correctness. To reason about Reo implementation formally, we introduce Timed Action Constraint Automata (TACA) and explain how to compare TACA with existing automata-based semantics for Reo. We use TACA to describe handshaking behavior of Reo modeling primitives and argue that in any distributed circuit remote Reo nodes and channels exposing such behavior commit to perform transitions envisaged by the network semantics.Comment: In Proceedings FOCLASA 2014, arXiv:1502.0315

Ultra-Reliable Communication in 5G Wireless Systems

Wireless 5G systems will not only be "4G, but faster". One of the novel features discussed in relation to 5G is Ultra-Reliable Communication (URC), an operation mode not present in today's wireless systems. URC refers to provision of certain level of communication service almost 100 % of the time. Example URC applications include reliable cloud connectivity, critical connections for industrial automation and reliable wireless coordination among vehicles. This paper puts forward a systematic view on URC in 5G wireless systems. It starts by analyzing the fundamental mechanisms that constitute a wireless connection and concludes that one of the key steps towards enabling URC is revision of the methods for encoding control information (metadata) and data. It introduces the key concept of Reliable Service Composition, where a service is designed to adapt its requirements to the level of reliability that can be attained. The problem of URC is analyzed across two different dimensions. The first dimension is the type of URC problem that is defined based on the time frame used to measure the reliability of the packet transmission. Two types of URC problems are identified: long-term URC (URC-L) and short-term URC (URC-S). The second dimension is represented by the type of reliability impairment that can affect the communication reliability in a given scenario. The main objective of this paper is to create the context for defining and solving the new engineering problems posed by URC in 5G.Comment: To be presented at the 1st International Conference on 5G for Ubiquitous Connectivit

Making the Distribution Subsystem Secure

This report presents how the Distribution Subsystem is made secure. A set of different security threats to a shared data programming system are identifed. The report presents the extensions nessesary to the DSS in order to cope with the identified security threats by maintaining reference security. A reference to a shared data structure cannot be forged or guessed; only by proper delegation can a thread acquire access to data originating at remote processes. Referential security is a requirement for secure distributed applications. By programmatically restricting access to distributed data to trusted nodes, a distributed application can be made secure. However, for this to be true, referential security must be supported on the level of the implementation

Modelling the GSM handover protocol in CommUnity

CommUnity is a formal approach to software architecture. It has a precise, yet intuitive mathematical semantics based on category theory. It supports, at the methodological level, a clear separation between computation, coordination, and distribution (including mobility). It provides a simple state-based language for describing component behaviour that is inspired by Unity and Interacting Processes. It also addresses composition as a first class concern and accounts for the emergence of global system properties from interconnections. This paper describes the approach and available tool support by modelling essential aspects of the GSM handover protocol. We also sketch a framework that we are implementing for the distributed execution of such specifications using Klava, a Java library for mobile agent systems based on tuple spaces