PERVASIVE computing 75 80 PERVASIVE computing Presentation Input sensor Coordinator Model Figure 4. Application framework infrastructure. The coordinator oversees the composition of the model, presentation, and controller components.82 PERVASIVE computing PERVASIVE computing 83 the AUTHORS Manuel Román is a PhD candidate at the University of Illinois at Urbana-Champaign. His research interests include ubiquitous computing, middleware, operating systems, and interactive and programmable active spaces. He received his BS and MS in computer science from the La Salle School of Engineering (Ramon Llull Univ.).

Conventional middleware systems fail to address important issues related to dynamism. Modern computer systems have to deal not only with heterogeneity in the underlying hardware and software platforms but also with highly dynamic environments. Mobile and distributed applications are greatly affected by dynamic changes of the environment characteristics such as security constraints and resource availability. Existing middleware is not prepared to react to these changes. In many cases, application developers know when adaptive changes in communication and security strategies would improve system performance. But often, they are not able to benefit from it because the middleware lacks the mechanisms to support monitoring (to detect when adaptation should take place) and on-the-fly reconfiguration. dynamicTAO is a CORBA-compliant reflective ORB that supports dynamic configuration. It maintains an explicit representation of its own internal structure and uses it to carry out runtime customization safely. After describing dynamicTAO's design and implementation, we discuss our experience on the development of two systems benefiting from the reflective nature of our ORB: a flexible monitoring system for distributed objects and a mechanism for enforcing access control based on dynamic security policies. There is nothing permanent except change. Heraclitus of Ephesus (535-475 BC) This research is supported by NSF grants 98-70736 and 99-70139. Fabio Kon is supported in part by a grant from CAPES-Brazil, proc.#1405/95-2.

Ubiquitous computing challenges the conventional notion of a user logged into a personal computing device, whether it is a desktop, a laptop, or a digital assistant. When the physical environment of a user contains hundreds of networked computer devices each of which may be used to support one or more user applications, the notion of personal computing becomes inadequate. Further, when a group of users share such a physical environment, new forms of sharing, cooperation and collaboration are possible and mobile users may constantly change the computers with which they interact; we refer to these digitally augmented physical spaces as Active Spaces. We present in this paper an application framework that provides mechanisms to construct, run or adapt existing applications to ubiquitous computing environments. The framework binds applications to users, uses multiple devices simultaneously, and exploits resource management within the users' environment that reacts to context and mobility. Our research contributes to application mobility, partitioning and adaptation within device rich environments, and uses context-awareness to focus the resources of ubiquitous computing environments on the needs of users.

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Abstract. The increasing software complexity and proliferation of distributed applications for cell phones demand the introduction of middleware services to assist in the development of advanced applications. However, from the user perspective, it is essential that these new phones provide a smooth error-free experience. Despite of the complexity underlying a cell phone, placing a phone call remains a simple task that can be performed by most users regardless of their technical background. Furthermore, cell phones rarely crash (especially compared to PCs) and carriers are able to correct certain problems remotely without user intervention. We advocate for a middleware infrastructure that allows carriers and developers to correct middleware behavior, configure it, and upgrade it, without requiring user intervention and without stopping the execution of applications. We introduce a new technique we refer to as externalization. This technique explicitly externalizes the state, the logic, and the internal component structure of middleware services. As a result, carriers and developers have full control over these middleware services. They can access, inspect, and modify the state, logic, and structure of middleware services at runtime while preserving the execution of existing applications and providing an error-free experience to users. We claim that externalization is the key for the future evolution of cell phones' middleware infrastructure.

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