LOTOS Process Research Articles

An Integrated Approach for Specification and Analysis of Functional and Performance Properties of Concurrent Systems

Considering both qualitative and quantitative aspects in the same modeling approach enhances coherency when analyzing concurrent system properties. Moreover, the impacts of changes related to functional and temporal features are generally better highlighted. In this paper, the authors present their approach to model and analyze behavioral and temporal properties of true concurrency systems. Compared to existing models, the underlying Maximality semantics allows to prune the state space. A specification language is also proposed, extending the LOTOS Process Algebra, in order to support any kind of action durations, like immediate, deterministic, Markovian or arbitrarily distributed ones.

Realizability of Choreographies Using Process Algebra Encodings

Service-oriented computing has emerged as a new software development paradigm that enables implementation of Web accessible software systems that are composed of distributed services which interact with each other via exchanging messages. Modeling and analysis of interactions among services is a crucial problem in this domain. Interactions among a set of services that participate in a service composition can be described from a global point of view as a choreography. Choreographies can be specified using specification languages such as Web Services Choreography Description Language (WS-CDL) and visualized using graphical formalisms such as collaboration diagrams. In this paper, we present an encoding of collaboration diagrams into the LOTOS process algebra for choreography analysis. This encoding allows us to (1) check the temporal properties of choreographies using a LOTOS verification tool set called the Construction and Analysis of Distributed Processes (CADP) toolbox, (2) check the realizability of choreographies for both synchronous communication and bounded asynchronous communication, and (3) automate the peer generation process. Realizability indicates whether peers can be generated from a given choreography specification in such a way that the interactions of the generated peers exactly match the choreography specification. If a collaboration diagram is unrealizable, our approach extends the peer generation process by adding extra communication that guarantees that the peers behave according to the choreography specification.

An Error Detection Method for Recursive Processes for LOTOS Instruction and Its Support System.

LOTOS, one of the formal description techniques, can strictly and unambiguously describe the requirement specifications of distributed systems such as protocols and communication systems. But it is difficult for beginners to learn and understand LOTOS. Thus, for LOTOS instruction support, we have already proposed an algorithm which can detect learner’s errors contained in the learner’s answer for some problems described in LOTOS. This algorithm is applied to non-recursive LOTOS processes. However, non-recursive processes cannot represent processes that execute events infinitely. In this paper, we propose a new algorithm which can support equivalence decision and error detection in recursive processes. We also present a software support system which aids this new algorithm.

Deriving CORBA Applications from Formal Specifications

This article describes an approach to the development of highly reliable and reusable CORBA applications. Interface description language (IDL) specifications are extended with LOTOS specifications of the functional and dynamic behavior of the interface operations. These extended interface specifications are compiled into header files and stub code using standard CORBA mechanisms. The LOTOS part can be compiled into C-code yielding prototype implementations. An extensible set of LOTOS tools is used to test and prove critical properties of distributed applications. From the event-oriented LOTOS description, a state-oriented program in a CSP-like programming language is derived. This program can be analyzed using very efficient, BDD-based model checking verification tools. Furthermore, it serves as an ideal intermediate step between verified, high level, reusable LOTOS processes which solve typical distributed programming tasks and their implementation as CORBA objects in production programming languages.

LANGUAGE FEATURES FOR COOPERATION IN AN OBJECT-ORIENTED DATABASE ENVIRONMENT

We introduce the language LOTOS/TM for the formal specification of a network of cooperating agents with a shared data repository and private local data. LOTOS/TM is the orthogonal integration of the process-algebraic protocol specification language LOTOS and the functional, object-oriented database specification language TM. The specified world consists of a number of interacting LOTOS processes — describing the cooperating agents — and a special LOTOS process representing the shared data repository, which is modeled as a TM database. The data repository's functionality is made available to the other, cooperating processes through one or more external database gates. Interaction at such a gate corresponds to a method invocation in the database. In addition to shared persistent data, the TM language is used to specify the data encapsulated locally within processes, and the transient data communicated over gates. Some features of LOTOS/TM are inherently suitable for describing cooperation, such as combinators for synchronization on specific methods. These features are illustrated by examples showing navigation events on a shared graph structure that resembles a hypertext. Emphasis in the examples is placed on coordination aspects of the scenario. LOTOS/TM serves as a formalism for a more user-friendly specification language by the name of CoCoA that is currently under construction.

LOEWE: A LOTOS engineering workbench

LOEWE is an integrated tools environment for the specification, analysis, and implementation of communication software. Although primarily based on the formal description technique LOTOS, LOEWE additionally offers multiple, semantically equivalent representations of a given protocol specification. Each format is specially adapted to support specific tool functionality: processes are used for simulation and compilation, fast state space exploration is performed on extended finite state machines, and labelled transition graphs are used for system verification. LOEWE currently contains a LOTOS syntax and static semantic verifier, a generator of extended finite state machines with associated interactive state exploration tools, a temporal logic verifier, a compiler to generate C code from LOTOS behavior expressions, a translator of LOTOS abstract data type operations to a set of LISP functions, and a graphical trace analyzer of LOTOS process interactions.

Rapid prototyping of protocols from LOTOS specifications

AbstractA new tool for generating implementation prototypes of communication protocols and concurrent systems specified using the ISO LOTOS language is presented in this paper. A brief introduction to LOTOS and a discussion of the main problems related to the efficient execution of specifications written in LOTOS are presented first. The design and implementation of the tool are then considered: LOTOS specifications are analysed and translated into C functions which are executed by co‐operating processes in the Unix environment. The set of LOTOS process definitions is first translated into a suitable number of extended finite‐state machines (EFSMs). The method proposed allows the problem of deriving unbounded EFSMs to be circumvented and a sort of control on the process number/size trade‐off to be obtained at the same time.The problem of implementing the LOTOS multi‐way rendezvous mechanism for process synchronization is solved by using an algorithm based on message‐passing techniques. An example of prototype derivation is also described, showing the form of C code generated by translating a simple specification. Finally, some performance figures are presented.

A common compiler for LOTOS and SDL specifications

This paper describes a translation of LOTOS and SDL specification languages into executable code, as it was prototyped in the Specification and Programming Environment for Communication Software (SPECS) project under the Research and Development in Advanced Communications in Europe (RACE) program. Both languages are translated into a common intermediate representation in the form of a network of state machines with both synchronous and asynchronous communications. By a series of transformations that make full use of the equivalence relations defined on LOTOS processes, this translation solves unique problems stemming from the highly abstract nature of LOTOS. The common intermediate representation is mapped into C code that can be executed in a specific run-time environment, implemented on a UNIX®-like operating system. SPECS has also developed a pragmatic approach to represent implementable data types in the algebraic framework of LOTOS and SDL, based on a set of predefined type constructors.

A protocol for multirendezvous of LOTOS processes

It is noted that the implementation of the multiway rendezvous mechanism of the International Standards Organization (ISO) LOTOS specification language for protocols is very important in the development of tools for the execution of LOTOS. It involves problems such as global knowledge in a distributed environment and distributed agreement. The authors propose a novel algorithm which fully implements the multiway rendezvous of LOTOS within a distributed execution model based on a number of parallel processes. The processes are organized in a hierarchical topology and communicate with each other only by message transfers. The performance of the proposed algorithm is evaluated and is shown to be better than that achieved by other algorithms proposed in the literature. A formal specification of the algorithm in LOTOS is provided. >