MobileTrans

There is a clear need for data sharing and collaboration support in a large number of computer applications in different domains. In this project, we focus on applications in the area of co-operative work within virtual organisations; for example, a virtual teaching community, a virtual enterprise grouping several companies from different countries, a widely distributed software development team, a distributed game involving people anywhere in the world, etc.

This need for information sharing will increase along two main axis: wide area (i.e., across the Internet) and mobility (i.e., portable computers, webpads, personal digital assistants, smart cellular phones, etc.). As a matter of fact, besides the growing number of desktop computers connected to the Internet, there are other devices, generally called information appliances (info-appliances), that are gaining enormous popularity; a personal digital assistant (PDA) is just one of them. The role of these info-appliances, currently handling calendars, phone numbers, etc. will certainly grow as more computing power and communications capability can be included creating new opportunities for mobile sharing and collaboration work.

The overall goal of this project is to facilitate the development and execution of distributed applications, running on top of PCs and info-appliances, that support data sharing and collaborative work within virtual organizations. To achieve this goal, system-specific issues, concurrency control and fault-tolerance in particular, must be handled automatically releasing the programmers of such task.

Until now, these system issues have been handled by means of transactions. However, the traditional ACID properties are too restrictive for the kind of sharing and collaborative work found in virtual organizations. In addition, they take into account neither the inherent mobility of info-appliances nor the characteristics of wireless networks (e.g., significant and rapid changes on the quality of service).

In mobile wide area networks, optimistic concurrency control is useful because pessimistic methods are inappropriate (e.g. a disconnected user cannot acquire or release locks). However, using an optimistic approach does involve some difficulties. In particular, long duration partitions will cause a greater incidence of apparent write-write conflicts than in stationary environments. It is therefore important to use application-specific semantic information to detect when such conflicts are false positives and can be avoided, or the data reconciled.

Thus, the contribution of MobileTrans is the design and implementation of a system capable of handling (possibly long running) transactions involving both wired and wireless info-appliances. A fundamental challenge is to understand how much does the classical transactional ACID model can/must be relaxed in order to be most adequate for sharing and collaboration within virtual organizations over wide area networks connecting a variety of distinct devices, from desktops to PDAs. Another challenge is to know where the computation should be done, in a mobile or in a stationary info-appliance, so that fault-tolerance and efficiency are not compromised; in fact, the mobility of users affects the placement of data and may require the dynamic and remote loading of code during the execution of transactions.

Sponsoring bodies: FCT

Coordinator: Paulo Ferreira

Partners: INESC-ID

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