Valeria Vittorini

The OsMoSys approach to multi-formalism modeling of systems

Analysis and simulation of complex systems are facilitated by the availability of appropriate modeling formalisms and tools. In many cases, no single analysis and modeling method can successfully cope with all aspects of a complex system: a multi-formalism multi-solution approach is very appealing, since it offers the possibility of applying the most suitable formalisms and solution techniques to model and analyze different components or aspects of a system. Another important feature that a successfull modeling approach should include is the possibility of reusing (sub)models: by composing parameterized submodels and then instantiating the parameters, complete models of different scenarios can be obtained and analyzed.This paper introduces an innovative approach to multi-formalism modeling of systems that is part of the OsMoSys (Object-based multi-formaliSm MOdeling of SYStems) framework. OsMoSys uses the proposed modeling approach to build multi-formalism models, and workflow management to achieve multi-solution. Our modeling approach is based on meta-modeling, allowing to easily define and integrate different formalisms, and on some concepts from object orientation. Its main objectives are the interoperability of different formalisms and the definition of mechanisms to guarantee the flexibility and the scalability of the modeling framework.

Vulnerability modeling and analysis for critical infrastructure protection applications

Abstract Effective critical infrastructure protection requires methodologies and tools for the automated evaluation of the vulnerabilities of assets and the efficacy of protection systems. This paper presents a modeling language for vulnerability analysis in critical infrastructure protection applications. The language extends the popular Unified Modeling Language (UML) to provide vulnerability and protection modeling functionality. The extended language provides an abstract representation of concepts and activities in the infrastructure protection domain that enables model-to-model transformations for analysis purposes. The application of the language is demonstrated through a use case that models vulnerabilities and physical protection systems in a railway station.

Model-driven availability evaluation of railway control systems

Maintenance of real-world systems is a complex task involving several actors, procedures and technologies. Proper approaches are needed in order to evaluate the impact of different maintenance policies considering cost/benefit factors. To that aim, maintenance models may be used within availability, performability or safety models, the latter developed using formal languages according to the requirements of international standards. In this paper, a model-driven approach is described for the development of formal maintenance and reliability models for the availability evaluation of repairable systems. The approach facilitates the use of formal models which would be otherwise difficult to manage, and provides the basis for automated models construction. Starting from an extension to maintenance aspects of the MARTE-DAM profile for dependability analysis, an automated process based on model-to-model transformations is described. The process is applied to generate a Repairable Fault Trees model from the MARTE-DAM specification of the Radio Block Centre - a modern railway controller.

Enabling the usage of UML in the verification of railway systems: The DAM-rail approach

The need for integration of model-based verification into industrial processes has produced several attempts to define Model-Driven solutions implementing a unifying approach to system development. A recent trend is to implement tool chains supporting the developer both in the design phase and V&V activities. In this Model-Driven context, specific domains require proper modelling approaches, especially for what concerns RAM (Reliability, Availability, Maintainability) analysis and fulfillment of international standards. This paper specifically addresses the definition of a Model-Driven approach for the evaluation of RAM attributes in railway applications to automatically generate formal models. For this aim we extend the MARTE-DAM UML profile with concepts related to maintenance aspects and service degradation, and show that the MARTE-DAM framework can be successfully specialized for the railway domain. Model transformations are then defined to generate Repairable Fault Tree and Bayesian Network models from MARTE-DAM specifications. The whole process is applied to the railway domain in two different availability studies.

Solution Workflows for Model-Based Analysis of Complex Systems

The development and analysis of increasingly complex systems require the intensive use of models and of sophisticated approaches to systems modeling. This paper focuses on workflows supporting the solution of complex, composed, formal models used to study and/or develop real-world systems. The workflows we deal with orchestrate multiple distributed tools and applications in order to provide the user with a powerful, composed solution environment. The aim is to automate and reproduce analysis and simulation tasks starting from a high level, graph-based description of the model to be solved. This paper thus introduces solution workflows and presents the Solution Process Definition Language (SPDL) for the specification of solution workflows processes. One of the key elements of SPDL is its formal semantics, which allow for unambiguous specification of its constructs and validation of the workflows. A workflow pattern analysis of SPDL is also provided. SPDL and its execution environment, the OsMoSys framework, are then applied to a homeland security scenario. The OsMoSys framework and the SPDL language provide a practical contribution to the applicability of model engineering techniques by enabling the semiautomatic solution of complex models.

Automatic Analysis of Control Flow inWeb Services Composition Processes

Composition of Web services is of great interest to support business-to-business collaboration and provide value added services with desired properties or capabilities. Nevertheless, the standard languages used to create business processes from composite Web services lack of formal definition of their semantics and tools to support the analysis of a business process. In this paper we provide a practical approach to formal verification of BPEL4WS executable processes. A syntax-driven operational semantics for BPEL4WS is introduced and an automatic verifier is presented in order to perform a semantic analysis of the flow constructs used in the definition of BPEL4WS processes

Towards Model-Driven V&V assessment of railway control systems

Verification and Validation (V&V) activities aiming at certifying railway controllers are among the most critical and time-consuming in system development life cycle. As such, they would greatly benefit from novel approaches enabling both automation and traceability for assessment purposes. While several formal and Model-Based approaches have been proposed in the scientific literature, some of which are successfully employed in industrial settings, we are still far from an integrated and unified methodology which allows guiding design choices, minimizing the chances of failures/non-compliances, and considerably reducing the overall assessment effort. To address these issues, this paper describes a Model-Driven Engineering approach which is very promising to tackle the aforementioned challenges. In fact, the usage of appropriate Unified Modeling Language profiles featuring system analysis and test case specification capabilities, together with tool chains for model transformations and analysis, seems a viable way to allow end-users to concentrate on high-level holistic models and specification of non-functional requirements (i.e., dependability) and support the automation of the V&V process. We show, through a case study belonging to the railway signalling domain, how the approach is effective in supporting activities like system testing and availability evaluation.

DrawNET++: Model Objects to Support Performance Analysis and Simulation of Systems

This paper describes DrawNET++, a prototype version of a model design framework based on the definition of model objects. DrawNET++ provides a graphical front-end to existing performance tools and a practical mean to study compositionality issues in multiformalism environments. The object oriented features of DrawNET++ provide a flexible architecture for structuring complex models.

Formal Specification of Concurrent Systems: A Structured Approach

CSP and Petri Nets are powerful formalisms for the specification and the analysis of concurrent systems. We present an approach to their integration to take advantage of both formalisms. In particular the GSPN class is used to address dependability and real-time aspects. In this paper an algorithmic transformation from a trace-based specification of a concurrent system to a Petri Net model is described. Causal dependencies between behaviours of the system components are introduced in the net model through the definition of external assumptions. The steps of the integration are illustrated by applying them to an unmanned transportation problem.

A MULTIFORMALISM MODULAR APPROACH TO ERTMS/ETCS FAILURE MODELING

European Railway Traffic Management System/European Train Control System (ERTMS/ETCS) is a recent standard aimed at improving performance, safety and inter-operability of modern railways. In order to be compliant to ERTMS/ETCS, a railway signalling system must meet strict nonfunctional requirements on system level failure modes. In this paper, a multiformalism model is employed to perform an availability analysis of an ERTMS/ETCS reference architecture at early phases of its development cycle. At this aim, a bottom-up analysis is performed from subsystem failure models (expressed by means of Generalized Stochastic Petri Nets, Fault Trees and Repairable Fault Trees) up to the overall system model. The modular approach, here used, allows to evaluate the influence of basic design parameters on the probability of system-level failure modes and demonstrates that system availability is within the bound required by the ERTMS/ETCS specification. The results show that the multiformalism modeling approach helps to cope with complexity, eases the verification of availability requirements and can be successfully applied to the analysis of complex critical systems.