Ambient computing applications: an experience with the SPREAD approach

Today, we assist to the explosive development of mobile computing devices like PDAs and cellphones, the integration of embedded intelligence (like Web server) in more and more common devices, and the proliferation of wireless communication technologies (IRdA, Bluetooth, IEEE 802.11, GPRS). All these trends contribute to move us closer to the ubiquitous computing world described by Mark Weiser. But while the technology is here, applications, and more important, models and tools for designing future ambient computing systems are still rare. One of the first innovative concepts of ubiquitous computing, context-awareness is still hard to use and understand from a programming perspective. We think that the problem resides in the lack of system support: in traditional computing, operating system offers simple to use and easy to understand abstractions of computational resources. Ubiquitous computing involves an integration of "computing" into the real-world, which is a radically different environment for applications. We think that this environment requires new operating system services and abstractions. Because the real world is made of physical entities, "living" in the physical space, ambient computing software should be able to use abstraction representing such objects, in a simple way. In this paper, we present a light framework to design ubiquitous computing software, called SPREAD. Unlike many approaches which hides too much of the real-world behind traditional computing abstraction, SPREAD defines programming abstraction based on the properties of the physical space. Hence, physical properties, like relative proximity, are used as implicitly in SPREAD as variable addressing in a computer memory. In SPREAD, application (or process) behavior can be "mechanically" driven, in the sense that actions flow can be directly dependent of physical mobility. To support this concept, we introduce a programming and execution model allowing designing computing and information systems driven directly by arranging and moving physical objects in the space. We demonstrate the use of the model to implement a few practical applications, highlighting its simplicity and expression power.