Basic Components for the Pattern Catalogue Sample Clauses

Basic Components for the Pattern Catalogue. ‌ To create the catalogue of patterns, we used two basic components (or patterns of component), de- scribed in the following and in a more detailed way in [Puv12]. These basic components showing dif- ferent adaptation capabilities, can be composed in different ways to create a number of self-adaptive patterns, either at the level of individual components or at the level of ensemble. A clear definition of their interfaces help in understanding the mechanism of composition. The “Reactive Service Component” is able to react to service requests. The component receives services’ requests as Input and replays to the service request with an Output. Inside the component there are some “actions” (A1, A2, . . . , An) that can be performed by the component, and a “logic” that selects the more appropriate action in order to satisfy a service’s request. The component is also situated in an environment and it can sense what is happening in the environment (and this can influence its actions) and can also act on the environment. We emphasize that the component’s reaction is mediated by such logic: this means that when a request R1 arrives, the component will initially respond with action A1; but if changes in the environment occur, the logic can choose another action (e.g. A2) that better responds at the same request R1. This new action is chosen in order to better satisfy the request, due to the adaptation of the component in reaction to external changes. The “Proactive Service Component” (PSC, and also called goal-oriented component) presents an internal feedback loop (see Figure 7). This component has a higher degree of autonomy, and thus of self-adaptation, than the Reactive. In fact, it can code internal goals that, along with the logic, can manage the choice of a specific action in response to the service request. The choice can depending on: (i) how close to the goal each action will bring it, possibly also based on the effects of past actions, and (ii) the current status of the environment in which it is situated. The internal structure for action selection based on goals, current status, and environment, makes the component structured as implicitly having a sort of internal autonomic feedback loop. It is worth mentioning that the behavior of both “Reactive Service Component” and “Proactive Service Component” can be related to the KnowLangs mechanism for knowledge representation for self- adaptive behavior where actions are picked based on past experience and con...