When different simulation units are coupled together there are different choices to take, in particular regarding the granularity of such a co-simulation. When prototyping systems, it is typically favourable to get an initial idea of how a collection of simulation units work together without spending too much time setting up the orchestration. However, the granularity of such a simulation may be far away from what is needed in relation to the purpose of the simulation. In order to enable more flexibility and control over the co-simulation it is necessary to be able to steer the orchestration in a more detailed manner. This paper presents an open source co-simulation orchestration engine based on the Functional Mockup Interface standard but with a Domain Specific Language (DSL) enabling detailed control between the individual simulation units. The same tool can thus be used right out of the box for low-granularity co-simulation, and for high-granularity simulation the DSL enable a significant flexibility.

The development of cyber-physical systems is heavily relying on model-driven approaches. After deployment, these models can be utilised in a Digital Twin setting, acting as virtual replicas of the physical components and reflecting the behaviour of the running system in real-time. Complex systems often consist of numerous models interacting with each other and individual models may need to be updated after deployment. This means that new models need to be integrated and swapped during runtime without interrupting the running system. In this paper, we propose an approach for model-based Digital Twins to replace individual models without stopping or halting the operation of a cyber-physical system. Furthermore, our approach allows to replace not only individual models, but also update the overall structure of the interaction of models in the Digital Twin setting. The use of the proposed mechanism is illustrated through two case-studies with an agricultural robot prototype.

Engineering complex Cyber-Physical Systems, such as emission reduction control systems for large two-stroke engines, require advanced modelling of both the cyber and physical aspects. Different tools are specialised for each of these domains and a combination of tools validating different properties is often desirable. However, it is non-trivial to be able to combine such different models of different constituent elements. In order to reduce the need for expensive tests on the real system it is advantageous to be able to combine such heterogeneous models in a joint co-simulation in order to reduce the overall costs of validation. This paper demonstrates how this can be achieved for a commercial system developed by MAN Diesel & Turbo using a newly developed tool chain based on the Functional Mock-up Interface standard for co-simulation supporting different operating systems. The generality of the suggested approach also enables future scenarios incorporating constituent models supplied by sub-suppliers while protecting their Intellectual Property.

We present and analyse an architectural migration in the Overture tool, a tool for which the primary internal data structure is an Abstract Syntax Tree (AST). The migration was from a high-cohesion AST with functionality encapsulated in its nodes to an extensible, low-cohesion AST with functionality implemented in visitors. This was motivated by the need for a high degree of extensibility in the tool's core functionality. We describe the migration process and both architectures in detail. We also present a comparative analysis between both architectures, including the trade-offs made between extensibility and performance. Finally, we generalise these results to other tool migrations that have hierarchical data structures at their core.

The formal modelling of System of Systems (SoS) is challenged by the autonomy of the participating constituent systems, as system owners may not be willing to share executable models that precisely describe their system's internals. This paper describes an approach for using distributed simulation within a collaborative development environment to enable the analysis of the entire SoS, without the detailed models of the constituent systems being shared.

Combinatorial testing in VDM involves the automatic generation and execution of a large collection of test cases derived from templates provided in the form of trace definitions added to a VDM specification. The main value of this is the rapid detection of run-time errors caused by forgotten preconditions as well as broken invariants and post-conditions. Trace definitions are defined as regular expressions describing possible sequences of operation calls, and are conceptually similar to UML sequence diagrams. In this paper we present a tool enabling test automation based on VDM traces, and explain how it is possible to reduce large collections of test cases in different ways. Its use is illustrated with a small case study.