Projects in Mobile Computing

Principal Investigator: P.K. Chrysanthis
Sources of Funding: National Science Foundation, CAREER Award IRI-9502091, B-Right Corp.

We developed a complete characterization of the mobile client and stationary database server interactions based on the notion of agreements which is a generalization of the escrow ideas in traditional distributed systems. Agreements allow sharing of data among mobile and stationary clients in a controlled fashion by specifying restrictions, obligations, and privileges which accompany the shared data.
We defined a canonical model for agreement based mobile transaction processing consisting of three functional components, namely, an agreement manager at the level of the server, mobility data manager at each mobility support station, and an agreement agent at each mobile computer. The agreement manager is responsible for all data and transaction management on a mobile computer. Using this canonical model, we developed a pro-active protocol for fragmentable objects which allows transactions to unilaterally commit on the mobile computer within the conditions of an agreement.

Some Relevant Publications:

G. Walborn and P. K. Chrysanthis. "Supporting Semantics-Based Transaction Processing in Mobile Database Applications.'' Proceedings of the 14th Symposium on Reliabl e Distributed Systems, September 1995.

Mobile Query by Icon

Principal Investigator: P.K. Chrysanthis
Sources of Funding: National Science Foundation RIA Award IRI-9210588 and CAREER Award IRI-9502091
Collaborators: Dipartimento di Informatica e Sistemistica, Universita' di Roma "La Sapienza".

We developed a prototype of a query processing facility that supports the exploration and query of databases from a mobile computer based on our theoretical work on {\em Query by Icon}. This satisfies all three of the criteria identified in the literature for an effective mobile query processing facility: (1) It allows the construction of a database query with no special knowledge of how the database is structured and where it is located. Its iconic visual query language does not involve path specification in composing a query. Thus, it is equally useful to both ordinary and expert mobile users. (2) Users primarily interact with the system with a pointing device, such as a pen or a mouse, and compose a query by arranging icons. Thus, it overcomes any size limitations of a mobile computer while new requirements are not imposed. (3) Complete queries are formulated on metadata stored on the mobile computer in an incremental manner and without involving access to the actual data in the remote database to materialize intermediate steps. Our developed algorithms, particularly the metaquery tools, are designed to effectively operate under limited memory and disk capacity, limited battery power, and restricted wireless communication bandwidth.

Some Relevant Publications:

A. Massari, S. Weissman, and P. K. Chrysanthis. "Supporting Mobile Database Access through Query by Icons'', Distributed and Parallel Databases Journal. Vol 4. pp. 1-21, 1996.