A lightweight multi-database execution engine

In this thesis, I describe the design and implementation of a lightweight multi database engine for data intensive Web applications. The engine was designed to provide structured querying (relational database access) to data from online data sources ranging from databases to semistructured documents. The implementation focused on allowing users to write queries, which would interface with distributed data, sources on the World Wide Web. One of the major problems dealt with was the automatic extraction and manipulation of data from distributed sources, taking into consideration the structural differences and data stored in semi-structured manner. The engine was implemented using an concurrent execution model that allowed much higher network parallelism compared to earlier versions of the system. Acknowledgements My final year at MIT has by far been the toughest, most enjoyable and edifying year. Writing this thesis allowed me to focus my skills on this project and realize that there are so many who support me. First of all I would like to thank the members of COIN research group. Professor Stuart Madnick and Dr. Michael Siegel gave me the opportunity to join this group and were a real support throughout. Dr. St6phane Bressan guided me from beginning to end, and was there to help with any problem that I had. I also thank the other, current and past members, of the Team such as Ahmed Ahzar, Tom Lee and Ozlem Ouzuner for being great a support. My family, although many thousands of miles away, would always magnify the good and downplay the bad. They prepared me to face these challenges and for that I give them all my thanks. My MIT friends were always there to help relax my mind, even when everyone was loaded with work. I thank them for that, and also for helping me to focus when it was so easy to stray. To my fiancee, Winnette McIntosh, through every day and night she has been there for me. Supporting me, encouraging and caring for me have been her tasks throughout, and she has been very successful at them all. I thank her for being here for me throughout this project and choosing to be with me forever. Finally and most importantly I thank God for everything, the opportunities that I have been given, the ability to make good on those opportunities, the grace God has given me to live a life with reference to him, the people he has put into my life and of course the strength to complete this project. Table of