Programming generic dynamic reconfigurations for distributed applications

Gerel is a generic reconfiguration language, which can be used to describe and implement dynamically reconfigurable distributed applications. Gerel is based on a powerful object selection mechanism for dynamically selecting configuration objects according to their structural properties, which are expressed in Gerel´s logic-based sublanguage Gerel-SL. Gerel also supports the definition of preconditions for programmed changes. These preconditions are evaluated at the beginning of the change´s execution and ensure that the current configuration has the structural properties required by the change. All these features of Gerel are shown in the scenario of a patient monitoring system. Due to its object selection mechanism supporting full first order logic expressions, Gerel has more expressive power than other reconfiguration languages and supports the definition of generic changes. This means that programmed changes can also be designed to be robust to system evolution. By providing change preconditions, Gerel also gives a means for defining reliable programmed reconfigurations, which are only executed if the current configuration is in a state expected by the change and whose execution need not be coordinated among the corresponding invoking components. Therefore, Gerel´s selection and precondition features support both re-usability of programmed changes for different domains and the strict separation of reconfiguration and application programming concerns