Simon Tjell

Formal requirements modelling with executable use cases and coloured Petri nets

This paper presents executable use cases (EUCs), which constitute a model-based approach to requirements engineering. EUCs may be used as a supplement to model-driven development (MDD) and can describe and link user-level requirements and more technical software specifications. In MDD, user-level requirements are not always explicitly described, since usually it is sufficient that one provides a specification, or platform-independent model, of the software that is to be developed. Therefore, a combination of EUCs and MDD may have potential to cover the path from user-level requirements via specifications to implementations of computer-based systems.

Requirements Engineering for Reactive Systems: Coloured Petri Nets for an Elevator Controller

This paper presents a model-based approach to requirements engineering for reactive systems; we use an elevator controller as case study. We identify and justify two key properties that a model which we construct must have, namely: (1) controller-and-environment-partitioned, which means constituting a description of both the controller and the environment, and distinguishing between these two domains and between desired and assumed behaviour; (2) use case-based, which means constructed on the basis of a given use case diagram and reproducing the behaviour described in accompanying scenario descriptions. For the case study, we build an executable model in the formal modelling language coloured Petri nets. We demonstrate how this model is useful for requirements engineering, since it provides a solid basis for addressing behavioural issues early in the development process, for example regarding concurrent execution of use cases and handling of failures.

Distinguishing Environment and System in Coloured Petri Net Models of Reactive Systems

This paper introduces and formally defines the environment-and-system-partitioned property for behavioral models of reactive systems expressed in the formal modeling language coloured Petri net. The purpose of the formalization is to make it possible to automatically validate any CPN model with respect to this property based on structural analysis. A model has the environment-and-system-partitioned property if it is based on a clear division between environment and system. This division is important in many model-driven approaches to software development such as model-based testing and automated code-generation from models. A prototypical tool has been implemented for performing the structural analysis of coloured Petri net models and the principles of this tool is described. The aim of the paper is to make the guidelines and their formalized definitions along with a proof-of-concept for the automatic validation of the structure of models based on structural analysis.

Model-based requirements analysis for reactive systems with UML sequence diagrams and coloured petri nets

In this paper, we describe a formal foundation for a specialized approach to automatically check traces against real-time requirements. The traces are obtained from simulation of coloured petri net (CPN) models of reactive systems. The real-time requirements are expressed in terms of a derivative of UML 2.0 high-level sequence diagrams. The automated requirement checking is part of a bigger tool framework in which VDM++ is applied to automatically generate initial CPN models based on problem diagrams. These models are manually enhanced to provide behavioral descriptions of the environment and the system itself.

Model-Based Analysis of a Windmill Communication System

This paper presents the experiences obtained from modeling and analyzing a real-world application of distributed embedded computing. The modeling language Coloured Petri Nets (CPN) has been applied to analyze the properties of a communication system in a windmill, which enables a group of embedded computers to share a group of variables. A CPN-based model of the system is used to analyze certain real-time properties of the system.

Expressing Environment Assumptions and Real-time Requirements for a Distributed Embedded System with Shared Variables

In a distributed embedded system, it is often necessary to share variables among its computing nodes to allow the distribution of control algorithms. It is therefore necessary to include a component in each node that provides the service of variable sharing. For that type of component, this paper discusses how to create a Colored Petri Nets (CPN) model that formally expresses the following elements in a clearly separated structure: (1) assumptions about the behavior of the environment of the component, (2) real-time requirements for the component, and (3) a possible solution in terms of an algorithm for the component. The CPN model can be used to validate the environment assumptions and the requirements. The validation is performed by execution of the model during which traces of events and states are automatically generated and evaluated against the requirements.