Paulo E. S. Barbosa

Ecore representation for extending PNML for Input-Output Place-Transition nets

This paper presents a metamodel for the Input-Output Place-Transition nets (IOPT nets), a Petri net class targeted at controllers modeling. The proposed metamodel reuses many of the elements of the Petri Net Markup Language (PNML) metamodel, such as places, transitions, and arcs; it extends the PNML metamodel for Place/Transition nets to comprise concepts inherent to IOPT nets. The IOPT nets metamodel is described in Ecore format, putting IOPT nets in the puzzle of MDA artifacts taking benefit from the MDA infrastructure.

Towards medical device behavioural validation using Petri nets

Medical devices development and validation are difficult activities due to the critical nature of these products, involving risks to the human lives. Moreover, regulatory agencies are increasing the control over companies because of the still huge number of harms caused for several reasons, having software failures as one of the main causes. Thus it is clear that more formal and sophisticated software development techniques should be investigated. In this paper, we show how Petri nets can play the role of a generic framework for architectural decisions for control systems, allowing besides verification/simulation, an important bridge in the requested traceability by regulatory bodies. We claim that it is possible to satisfy traceability from architectural elements to code, test cases, functional and safety requirements and so on. In order to make clear our point, we conducted a case study from a generic infusion pump specification.

An Extended MDA Architecture for Ensuring Semantics-Preserving Transformations

MDA is a current trend that shifts the focus and effort from implementation during the development process to models, metamodels and transformations. The four-layer MDA architecture still suffers from the lack of formalization of its artifacts and processes leading to ambiguity and low reliability problems. For instance, currently there is no way for ensuring that MDA transformations are semantic-preserving. In this paper we tackle this problem by incorporating well-consolidated formal methods approaches in the MDA architecture. We propose extending the M1 and M2 layers of the MDA architecture towards the definition of static and dynamic semantic models, both crucial to extract the semantics of any model. The extension includes: (i) a semantic metamodel and a set of transformations representing semantic equations; and (ii) a set of evaluation reduction rules for semantic models in order to extract the meaning from their states and automatic proofs of conformance between these models. In order to validate this work, a proof of concept has been implemented and evaluated verifying conformance between models that represent imperative constructs of programming languages in the modelware context.

Properties Preservation in Distributed Execution of Petri Nets Models

Model-based development for embedded system design has been used to support the increase of system’s complexity. Several modeling formalisms are well matched for usage within this area. One of the goals of this work is to contribute to the usage of Petri nets as system specification language within model-based development of embedded systems having MDA proposals as a reference for the development flow. Distributed execution of the Petri net model is achieved through model partitioning into sub-modules. System decomposition is obtained through net splitting operation. Two types of implementation platforms were considered: compliant and non-compliant with zero time delay for communication between modules. Using model-checking techniques, properties associated with the execution of the distributed models in both types of platforms were compared with the execution of the initial (centralized) Petri net model.

SysVeritas: A Framework for Verifying IOPT Nets and Execution Semantics within Embedded Systems Design

We present a rewriting logic based technique for defining the formal executable semantics of a non-autonomous Petri net class, named Input-Output Place/Transition nets (IOPT nets), designed for model-based embedded system’s development, according to the MDA initiative. For this purpose, we provide model-to-model transformations from ecore IOPT models to a rewriting logic specification in Maude. The transformations are defined as semantic mappings based on the respective metamodels: the IOPT metamodel and the Maude metamodel. Also, we define model to-text transformations for the generation of the model execution code in the rewriting logic framework. Hence, we present a translational semantics composed by two components: (i) the denotational one, considering as semantic domains the operations, equations, and properties that specify the Petri net structure, signals, and events according to the commutative monoid view; and (ii) the operational one, that changes the interleaving semantics of Maude using rewriting rules specified at the Maude metalevel to provide a maximal step semantics for transitions with arcs, test arcs, and priorities. Additionally, this work gives architectural advices in order to compose new semantics specifications by simple component substitution. Due to its simulation and verification capabilities for control systems, the presented work was applied to a domotic project that intends to save energy in residential buildings.

Petri Net Based Specification and Verification of Globally-Asynchronous-Locally-Synchronous System

This paper shows a methodology for Globally-Asynchronous-Locally-Synchronous (GALS) systems specification and verification. The distributed system is specified by non-autonomous Petri net modules, obtained after the partition of a (global) Petri net model. These modules are represented using IOPT (Input-Output Place-Transition) Petri net models, communicating through dedicated communication channels forming the GALS system under analysis. This set of modules is then automatically translated into Maude code through a MDA approach. As the modules of GALS systems run concurrently, the Maude semantics for concurrent objects is used along with message representation. Finally, as a particular case, the system state space is generated from the Maude specification of the GALS system, allowing property verification.

A Bag-of-Tasks Approach for State Space Exploration Using Computational Grids

A strategy for exploring distributed state spaces using computational grids that run bag-of-task applications is discussed. The main idea is to use computational grid tools as a layer between the verification tool and the distributed shared resources, aggregating the vast background developed by researchers in grid computing. Hence, the computational grid deals with resource scalability, computational speedup, and reliability in a transparent manner for the verification tool. Experimental results using a state space generation tool for an object-oriented Petri nets and the OurGrid solution show that is possible to achieve speedup applying it to a private network environment. Moreover, when a wide distributed community is considered, the model size can be increased several times

Testing from Structured Algebraic Specifications: The Veritas Case Study

The use of algebraic specification-based testing to validate applications implemented in SML is discussed, particularly the Veritas model-checker. Test case, oracle and data are generated from structured specifications in Casl with test oracles being responsible for driving and interpreting the results of tests according to fundamental research in the area. The objective of this work is twofold - to test conformance of the Veritas model checker with respect to a structured algebraic specification, and to contribute to further development in the area of specification-based testing by illustrating its application, focusing on theoretical problems and solutions anticipated.

The Safety Requirements Decomposition Pattern

Safety requirement specifications usually have heterogeneous structures, most likely based on the experience of the engineers involved in the specification process. Consequently, it gets difficult to ensure that recommendations given in standards are considered, e.g., evidence that the requirements are complete and consistent with other development artifacts. To address this challenge, we present in this paper the Safety Requirements Decomposition Pattern, which aims at supporting the decomposition of safety requirements that are traceable to architecture and failure propagation models. The effectiveness of the approach has been observed in its application in different domains, such as automotive, avionics, and medical devices. In this paper, we present its usage in the context of an industrial Automated External Defibrillator system.

A Model for Architecture Centric Development of Automated External Defibrillators

Due to complex safety requirements, medical devices must obey rigorous standards. In the development of these devices, modeling techniques must be used to analyze the design decisions in agreement with such standards. In this paper, we present a Matlab/Simulink specification as an analytical model for Automated External Defibrillators (AEDs) and its integration with a Model Based Systems Engineering (MBSE) approach through descriptive models. The proposed model allows us to analyze algorithms for decision of shock application, performance of circuits when obtaining the required voltage, safety of the produced energy for shock delivery and characteristics of signals produced at the output of the AED. The model is composed of modules with interfaces specification, allowing safe module replacement and the assessment of the module influence over the system at a technical level.