Architectural Reflection: Bridging the Gap Between a Running System and its Architectural Specification

As the size and complexity of software systems increase, a relevant part of the system overall functionality shifts from the applicative domain to run-time system management activities, i.e., management activities which cannot be performed off-line. These range from monitoring to dynamic reconfiguration and, for non-stopping systems, also include evolution, i.e., addition or replacement of components or entire subsystems. In current practice, run-time system management is impeded by the fact that the knowledge of the overall structure and functioning of the system (i.e., its software architecture) is confined in design specification documents, while it is only implicit in running systems. In this paper we introduce, provide rationale for, and briefly demonstrate an approach to system management where the system maintains, and operates on, an architectural description of itself. This description is causally connected to the system’s concrete structure and state, i.e., any change of the system architecture affects the description, and vice versa. This model can be said to extend the principles of computational reflection from the realm of programming-in-the-small to that of programming-in-thelarge.