Report Number: CS-TN-95-27
Institution: Stanford University, Department of Computer Science
Title: Comparing Very Large Database Snapshots
Author: Labio, Wilburt Juan
Author: Garcia-Molina, Hector
Date: May 1995
Abstract: Detecting and extracting modifications from information sources is an integral part of data warehousing. For unsophisticated sources, in practice it is often necessary to infer modifications by periodically comparing snapshots of data from the source. Although this snapshot differential problem is closely related to traditional joins and outerjoins, there are significant differences, which lead to simple new algorithms. In particular, we present algorithms that perform (possibly lossy) compression of records. We also present a window algorithm that works very well if the snapshots are not "very different". The algorithms are studied via analysis and an implementation of two of them; the results illustrate the potential gains achievable with the new algorithms.