A deployment (nested) is a visual synonym of a deployment. It is an alternative and useful way of expressing the deployment relationship. It is often more visually appealing to audiences not familiar with the UML as the containment of an artifact inside a deployment target such as a node is easier to understand. When there are a large number of artifacts deployed to a particular deployment target it is often more appropriate to use the deployment relationship in its linear form as the contents of the deployment target can become congested.
A device is a type of node. It is a physical resource and has the power to perform computations. Artifacts and components can be deployed to a device and typically rely upon services offered by the device to carry out their work. A device may be composed of other devices as part of a hierarchy of nested devices.
An execution environment is a type of node. It is a logical resource that acts as a location to deploy specific types of artifacts and components, and has the power to perform computations. Artifacts and components can be deployed to an execution environment and typically rely upon services offered by the execution environment to carry out their work.
A node instance represents a distinct instance of a node. It is an actual instance of a resource that carries out the work of the system. It has unique identity as well as attribute values, which determine its state at any point in time. A node instance can exhibit behavior, but only as a result of being an instance of a node. A node instance is an instance of one (and only one) node.