A resource usage represents any usage of resources in its broadest meaning, for example a usage of a product realized by a resource. <br/>A service usage represents any usage of service in its broadest meaning, for example or a usage of a service that realizes a product. <br/>A Product is realized as one or more Service(s) and/or Resource(s). A Product is created by instantiating a ProductOffering and adding it to a specific customer account. In order to charge a service (or a resource) usage, the service (or resource) has to be associated to a product. <br/>The product usage describes the usage of an instantiated Product.<br/>Theoretically there are many different ways to model resource, service and product usage. For example:<br/><ul>
<li>As classes that inherited from Usage class.</li><li>As different states of the same Usage class.</li></ul>
The following Figure describes the first approach where ResourceUsage, ServiceUsage and ProductUsage usage abstract templates inherited from Usage class.<br/>