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What is Event-Based Systems

Encyclopedia of Information Science and Technology, Second Edition
Systems in which clients ( subscribers ) have to express ( subscribe ) their interest in receiving particular events. Once clients have subscribed, servers ( publishers ) publish events, which will be sent to all interested subscribers.
Published in Chapter:
Adaptive Mobile Applications
Thomas Kunz (Carleton University, Canada) and Abdulbaset Gaddah (Carleton University, Canada)
DOI: 10.4018/978-1-60566-026-4.ch005
Abstract
The convergence of two technological developments has made mobile computing a reality. In the last few years, developed countries spent large amounts of money to install and deploy wireless communication facilities. Originally aimed at telephone services (which still account for the majority of usage), the same infrastructure is increasingly used to transfer data. In parallel, wireless LAN technologies are providing hotspot coverage in many high-traffic locations. The second development is the continuing reduction in size of computer hardware, leading to portable computation devices such as laptops, palmtops, or functionally enhanced cell phones. Given current technology, a user can run a set of applications on a portable device and communicate over a variety of communication links, depending on his/her current location. As will be explained in more detail later on, the mobile computing environment is highly dynamic. Available bandwidth changes by orders of magnitudes, based on the selected wireless access technology. Also, portable devices differ in processing power, memory, display capabilities, and other characteristics. It is generally argued that applications should “adapt” to the current environment, for example by filtering and compressing data or by changing the functionality offered to the user. Some researchers even argue that all future applications, not just the ones intended for execution on mobile devices, will have to be able to adapt to changing requirements and changing implementation environments on time scales from microseconds to years (Kavi, 1999). This article reviews the work on adaptive mobile applications and provides an outlook on future trends. The alternative to adaptive applications is to either implement a single application that is designed for the lowest common denominator (in terms of resource availability) or multiple functionally identical or similar binaries, tuned for specific environments. The former will needlessly sacrifice application features when running in more resource-rich environments. The latter approach is an inferior solution as well, for a number of reasons. The user of a portable device has to install and maintain multiple applications, which is a drain on the limited storage capabilities typically found on those devices. It also potentially results in different user interfaces and causes high software development overheads when developing the “same” mobile application multiple times. Finally, it forces the user to identify the current execution conditions and select the “right” application. The next section will review the motivation for adaptive approaches towards mobile application design. We will then briefly review traditional approaches to adaptive mobile applications, followed by a discussion of mobile middleware that is intended to support adaptive mobile applications. The article finishes with a brief conclusion of the state-of-the-art and identifies areas of future work.
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