"Model-Based Semantic Compression for Network-Data Tables"

by Shivnath Babu, Minos Garofalakis, Rajeev Rastogi, and Avi Silberschatz.
Proceedings of NRDM'2001, Santa Barbara, California, May 2001.


While a variety of lossy compression schemes have been developed for certain forms of digital data (e.g., images, audio, video), the area of lossy compression techniques for arbitrary data tables has been left relatively unexplored. Nevertheless, such techniques are clearly motivated by the ever-increasing data collection rates of modern enterprises and the need for effective, guaranteed-quality approximate answers to queries over massive relational data sets. In this paper, we propose Model-Based Semantic Compression (MBSC), a novel data-compression framework that takes advantage of attribute semantics and data-mining models to perform lossy compression of massive data tables. We describe the architecture and some of the key algorithms underlying SPARTAN, a model-based semantic compression system that exploits predictive data correlations and prescribed error tolerances for individual attributes to construct concise and accurate Classification and Regression Tree (CaRT) models for entire columns of a table. More precisely, SPARTAN selects a certain subset of attributes for which no values are explicitly stored in the compressed table; instead, concise CaRTs that predict these values (within the prescribed error bounds) are maintained. To restrict the huge search space and construction cost of possible CaRT predictors, SPARTAN employs sophisticated learning techniques and novel combinatorial optimization algorithms. Our experimentation with several real-life data sets has offered convincing evidence of the effectiveness of SPARTAN's model-based approach -- SPARTAN is able to consistently yield substantially better compression ratios than existing semantic or syntactic compression tools (e.g., gzip) while utilizing only small data samples for model inference. Several promising directions for future research and possible applications of MBSC in the context of network management are identified and discussed.

[ paper (ps.gz) | Shivnath's talk slides (ppt.gz) ]