## 7 Experimentation of ArTIC-MS: Federation with OCEAN  
As discussed in Section 1, the main objective of this paper is the complete specification of ArTIC-MS, a conceptual architecture aiming to foster the FAIR principles in MSaaS environments. In this respect, a preliminary evaluation of the soundness of principles on the basis of ArTIC-MS has been discussed in [12]. Specifically, such an analysis has addressed the following issues:  
* The availability of existing software products for developing TOSCA templates;
* The availability and usability of IaaS cloud implementations compliant with TOSCA;
* The effectiveness of the HOT translator component, for mapping TOSCA templates to HEAT-based ones. Differently, in this work, experimentation was carried out as part of MASTER, a research project developed under the National Program for Defense Research, which aims to define innovative solutions for developing M&S applications in the cloud. A prototype MSaaS concrete implementation based on the TOSCA-compliant IaaS platform Alien4 Cloud [31] and compliant with ArTIC-MS has been developed. Then, a heterogeneous MSaaS federation has been built by federating the ArTIC-MS prototype with OCEAN [15], a MSaaS platform based on the open-source OpenStack cloud infrastructure [16]. As ArTIC-MS focuses on infrastructure orchestration, the experimentation has not addressed the evaluation of measurable simulation-related performance parameters (e.g., the simulation execution time or the speed-up). Rather, it has been conducted to assess how ArTIC-MS is able to support the FAIR principles in the development of a MSaaS-based application, by (i) easing the discovery of services in a heterogeneous federation (findability), (ii) retrieving the required M&S resources throughout a metadata-based discovery (accessibility, and (iii) improving the interoperability and reusability of M&S resources thanks to the adoption of TOSCA. The experimentation has addressed the simulation of a maritime defense scenario, as depicted in Figure 12. The simulation includes two M&S services: a _scenario generator_ available from the TOSCA-based ArTIC-MS prototype implementation, and a _naval simulator_, which is managed by OCEAN. Figure 11: Federation of heterogeneous MSaaS infrastructure. The architecture of the adopted OCEAN implementation is depicted in Figure 13.  
OCEAN provides a visual interface to specify templates by composing the several elements (software artifacts, computing nodes, network connections, etc.) available from a dedicated toolbox and includes a feature for searching existing services that can be used as building blocks of more complex composed services. As an OpenStack-based implementation, OCEAN makes use of the orchestration engine HEAT to parse topology templates specified by the use of the HOT description format, which is based on YAML. The experimentation addresses the use case discussed in Section 6.2 and specifically focuses on the portability of TOSCA-based M&S services onto the OCEAN infrastructure. Specifically, Figure 14 shows the sequence of activities and the flow of information exchanged between the two federated infrastructures. _User A_, which acts as a _service provider_, is responsible for developing the _scenario generator_ service, specifying the relevant TOSCA-based template and creating the CSAR package to make the M&S available to other users, as discussed in Section 6, by using the ArTIC-based infrastructure platform (upper part of the figure). _User B_, which acts as the simulation developer, is responsible for developing the required simulation which addresses the maritime defense scenario illustrated in Figure 12, by identifying, retrieving, deploying, and orchestrating the required M&S services, e.g., the _scenario generator_ and the _naval simulator_. Specifically, the experimentation has been carried out as follows:  
_Precondition: executable artifacts implementing the Scenario Generator service are available for User A._  
1.