Reflective Middleware: From Your Desk to Your Hand

Communication middleware simplifies the construction of component-based distributed applications [1] [2]. However, the lack of flexibility in the construction of the middleware itself imposes limitations and is a major concern [3-7]. While applications can detect changes in their execution environment, they cannot customize the underlying middleware to better accommodate these changes. To solve this problem, recent research in reflective middleware [8] uses techniques derived from previous work in computational reflection to add flexibility to middleware. Reflective middleware exploits the concept of the meta-object protocol introduced by Kickzales [9]. The approach combines the ideas of computational reflection and object-orientation. His model distinguishes between base level and meta-level objects. The base level concerns the functional aspects of a system while the meta-level concerns aspects that include policies, mechanisms, or strategies. The base level of a reflective middleware addresses the functionality of the application program while the meta-level designates collections of components that form the internal architecture of the middleware platform. Reflection can inspect and modify these components and change the behavior of the middleware. As computer networks become pervasive and portable and as embedded and handheld devices become more common, ubiquitous computing will allow mobile users to benefit significantly from a plethora of ubiquitous services. However, ubiquitous computing is characterized by constant change and a large degree of dynamism. Users will interact with heterogeneous systems using different devices at different locations over different networks with different quality of service requirements. They will share the systems with many other users. In practical terms, it is difficult to devise a fixed set of policies and mechanisms for communication, security, and resource allocation that would accommodate such diversity, change, and scale. Reflective middleware offers effective flexibility in these highly dynamic environments. This article begins with the presentation of our previous work in reflective middleware. We then describe a vision of reflective middleware as one of the enabling technologies for ubiquitous computing. Next, we analyze the specific requirements that ubiquitous computing imposes on reflective middleware architectures. We provide a description of our ongoing work on Active Spaces that exploits “dynamicTAO”, a reflective CORBA ORB and the “Universally Interoperable CoreTM” – a small, innovative reflective ORB.