System Architecture Design

pSHIELDSystem Architecture DesignPUto decide whether a specific functionality must be supported by each Embedded System Device (ESD). Itis obvious that the more ESDs are equipped with the pSHIELD Middleware Adapter (resulting to be a pS-ESD), the more will be the coverage area and the effectiveness of the pSHIELD functionalities toguarantee a certifiable SPD level (based on common shared SPD metrics) over the whole system.Let’s see more in detail the formalized conceptual model of the Core SPD services, detailing thearchitecture depicted in previous figure and exploding the core SPD services into their functionalcomponents.InnovativeSPD MiddlewareFunctionalitiesSPDSecurityAgentpS MSpS MSpShieldNetworkAdapterCore SPD ServicespS NSServiceRegistryORCHESTRATIONSemantic DBpS NCCOMPOSITIONpShieldNodeAdapterDISCOVERYFigure 31 – Core SPD services in the pSHIELD functional component architecture.Apart from the Discovery, Composition and Orchestration components already described in the previoussection, the following additional conceptual entities have been introduced:• Service Registry: it acts as a database to store the service entries. Any pSHIELD Node, Networkor Middleware layer component can be registered here to be discovered• Semantic DB (Database): it holds any semantic information related to the pSHIELD components(interface, contract, SPD status, context, etc.). The use of common SPD metrics and of a sharedontology (derived from the formalized semantic model) to describe the different SPD aspectsinvolved in guaranteeing a precise level of SPD, allows to dominate the intrinsic heterogeneity ofthe SPD components. Any semantic data is thus technology neutral and it is used to interface withthe technology independent mechanisms applied by the pSHIELD OverlayFocusing exclusively on the Core SPD services located in the pSHIELD Middleware Adapter, we candescribe how it works when it is in an operative status. Let’s consider a typical situation, where the wholesystem is properly working at runtime. The Orchestration functionality is in charge to monitor continuouslythe Semantic DB with the updated status of the functionalities operating at node, network and middlewarelayers. The pSHIELD Adapters are in charge to update in the Semantic DB their status.Whenever the needed application SPD level changes and goes beyond the threshold, for any reason (e.g.due to external/internal unforeseen/ predictable events), the Orchestrator triggers the Overlay. TheOverlay tries to react and to restore the SPD level back to an acceptable level identifying the bestconfiguration rules. The Discovery and Composition are then triggered by the pSHIELD Overlay with theaim to apply the configuration rules. On the basis of the configuration rules, the Composition servicePUD2.3.2Issue 5 Page 102 of 122