Research Highlights: Bridging Theory and Practice with Query Log Analysis

Take a database conference paper and search for "in the real world" in it; chances are high you will find it. Of course what is real depends on one's perspective: for a pure theory paper it could be what one saw in a systems paper, for a systems paper it could be an issue that implementors of DBMSs had to deal with, and for the latter it may be what the customers need. But to sharpen our research tools, it helps tremendously to understand that the real "real world" is, and adjust our (sometimes very elaborate) techniques to address problems that actually occur. A nice example of this is analyzing the computational complexity of database queries. Database theory has developed an arsenal of tools for this. We know that for many classes of queries, the complexity is roughly kDkO(kQk) for a database D and a query Q, where k k means size. Thus, much research went into the detailed analysis of the structure of queries that removes kQk from the exponent and replaces it by a small fixed constant. We have a very good theoretical understanding of such classes, but we know much less about their relationship with queries that real-world users write.