## 5 Architecture for the TOSCA-Based Inter-Cloud M&S (ArTIC-MS)
### ArTIC-MS Conceptual Architecture  
ArTIC-MS conceptual architecture, which is shown in Figure 4, consists of the following building blocks:  
* **Web-based user interface:** Provides a web-based visual interface that allows users to make use of the capabilities provided by other ArTIC-MS building blocks. * **Composer:** Provides a visual environment to create the MSaaS application by composing the required services. * **Deployment handler:*
* Provides the capability to carry out the following activities:
* The configuration of required parameters for each concrete M&S service included in the MSaaS application;
* The configuration of each computing node that composes the execution platform;
* The specification of the required configurations specifying how M&S services have to be deployed onto the execution platform. * **Repository interface:** Provides an interface to access the repository service. * **Registry interface:** Provides an interface for accessing the registry service. * **Federated service discovery:** Provides a visual environment that allows users to perform federated service discovery. This building provides the capability for executing inter-cloud M&S service discovery by exploiting the registry services API made available by each federation's participant. * **Cloud infrastructure interface:** Provides the ability to interact with the underlying cloud infrastructure. * **Services repository:** Provides the capability for storing actual M&S services implementations. * **Services registry:** Provides the capability for storing M&S services descriptions. * Deploy the service implementation on top of the required execution platform, according to the topology template specification;
- Start the service by invoking the required life-cycle operations provided by the executable artifacts. * **Service description translator:** Provides the capability for parsing and translating a YAML-based TOSCA service template to make it compliant with non-TOSCA cloud implementations, and vice versa. To better clarify the relationship between the RA and ArTIC-MS it should be underlined that the RA specifies an abstract template for guiding the development of concrete MSaaS infrastructure implementations, while ArTIC-MS is a _conceptual architecture_ which _refines_ the RA in order to achieve the following objectives:  
* The explicit adoption of TOSCA, which is acknowledged to be a promising standard for supporting the interoperability of M&S services in heterogeneous MSaaS federation;
* The specification of appropriate use cases, in order to describe how the composition, deployment and orchestration of M&S services in a federated MSaaS infrastructure is dealt;
* The identification of abstract components constituting the backbone of any MSaaS infrastructure implementation based on TOSCA. Regarding the last point, it should be underlined that, in order to keep the proposed solution as abstract as possible, the RA itself has been specified in terms of interacting services that provide the required capability, according to the MSaaS paradigm. Differently, ArTIC-MS identifies appropriate _components_ which have to be included in any concrete architecture deployed as part of the MSaaS infrastructure implementation. As an example, the RA introduces a _capability_ provided by the _registry service_ which, from a MSaaS perspective, might be available in a catalog of existing M&S services. Differently, ArTIC-MS includes a _registry component_ that must be included in any compliant concrete architecture  
Figure 4: Conceptual architecture of ArTIC-MS.  
and, consequently, implemented as an actual repository capable of storing YAML-based service templates. Thus, the adoption of ArTIC refines the layered architecture principle introduced in Section 4.2, as shown in Figure 5.  
Three different layers have to be considered:  
* **Abstract architecture layer:*
* Describes an abstract architecture, which has been specifically defined to cope with a given application domain.