Application of software framework technology to an antenna pointing controller

Software frameworks are a reuse technology that makes architectural (as opposed to code) reuse possible. They have been successfully applied in the desktop and commercial arena but have so far been eschewed in the space sector. Alenia Spazio, as part of a drive to increase software reuse, have started a pilot project to develop the software for an Antenna Pointing Controller (APC) using framework technology. This work is done with P&P Software of Germany and takes as a starting point the AOCS Framework. The paper describes the experience acquired and the lesson learned applying the framework technology to the APC project. The first part gives an overview of object-oriented frameworks in general and of the AOCS Framework in particular. The second part describes the APC Framework, its close likeness to the AOCS Framework and the methodological and implementation issues that arose in the application of framework technology to an Antenna Pointing Controller. 1. Object-Oriented Software Frameworks Software frameworks [Pre95, Fay99] promote the reuse of entire architectures within a narrowly defined application domain. They propose an architecture that is optimized for all applications within this domain and make its reuse across applications in the domain possible. Frameworks can also be seen as generative devices: they serve as a basis from which applications can be rapidly instantiated. Figure 1 shows a typical view of an application generated from a framework. The shaded block represents the architectural backbone of the application. This is invariant in the application’s domain and is provided by the framework. The unshaded blocks provide the application-dependent behaviour. They customize the framework by being combined with it during the instantiation process. The essential property of a framework is its adaptability. A framework exists solely to be adapted to match the needs of a specific application within its domain. The points where adaptation takes place are called hot-spots. In an object-oriented framework, two adaptation mechanisms are used: inheritance and object composition. Although frameworks can and have been built using other adaptation techniques (such as Ada generics), the experience from the commercial sector is that inheritance and objectcomposition are the only mechanisms that offer sufficient flexibility to adapt the behaviour