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Abstract

resources We provide abstract interfaces, amenable to both users and applications, through (virtual) file trees. Unlike other systems that use files for interfaces (Plan 9, for example), we don't provide pixmaps or other low-level artifacts to support GUIs. We support user interfaces by providing a file tree in which a different file represents each UI element (that is, widget). The same applies to other resources.These files aren't on disk but are provided by resource servers, such as in Plan 9 or Unix's /proc. 3 In addition, we don't propose to intercept file system calls. Rather, we take the Plan 9 approach to the limit and provide all services by implement- Plan B maps abstract interfaces to files and adapts to file tree availability. It is easy to program, offers a general-purpose computing environment, and supports smart spaces without using middleware.The system ensures that the namespace reflects which resources are available and which ones aren't, cleanly removing unavailable resources from the file trees. JULY-SEPTEMBER 2007 PERVASIVE computing 63 Figure 2. A typical Plan B screen, serviced by the Omero UI volume.

There is a huge effort in ongoing research on new middleware platforms and new distributed services to support ubiquitous environments and pervasive applications. Most research projects mention concrete applications or demonstrators used to back up the claimed need for a new particular service, piece of software, or middleware layer. However, we have found that in many cases we could easily build such applications by relying on services already provided by the system we use daily, Plan 9 from Bell Labs. This paper explores how far can we go with a traditional system to support an ubiquitous environment, with no need for new services. We describe how we used Plan 9 to make our environment become ubiquitous. We describe as well what limits we found, and what technology could be used to overcome them.

Abstract