Events & News
Colloquium
| Category | Lecture |
| Date | Wednesday, April 29, 2009 |
| Time | 2:00 pm |
| Location | GS 701 |
| Details | PhD Thesis Committee: Chair, Richard Snodgrass Bongki Moon Christian Collberg |
| Speaker | Dengfeng Gao |
| Title | PhD Thesis Defense |
| Affiliation | Computer Science Department |
Supporting the Procedural Component of Query Languages over Time-Varing Data
As everything in the real world changes over time, the ability to model this temporal dimension of the real world is essential to many computer applications. Almost every database application involves the management of temporal data. This applies not only to relational data but also to any data that models the real world including XML data. Expressing queries on time-varying (relational or XML) data by using standard query language (SQL or XQuery) is more difficult than writing queries on nontemporal data. In this dissertation, we present minimal valid-time extensions to XQuery and SQL/PSM, focusing on the procedural aspect of the two query languages And efficient evaluation of sequenced queries
For XQuery, we add valid time support to it by minimally extending the syntax and semantics of XQuery. We adopt a stratum approach which maps a tauXQuery query to a conventional XQuery. The first part of the dissertation focuses on how to perform this mapping, in particular, on mapping sequenced queries, which are by far the most challenging. The critical issue of supporting sequenced queries (in any query language) is time-slicing the input data while retaining period timestamping. Timestamps are distributed throughout an XML document, rather than uniformly in tuples, complicating the temporal slicing while also providing opportunities for optimization. We propose five optimizations of our initial maximally-fragmented time-slicing approach: selected node slicing, copy-based per-expression slicing, in-place per-expression slicing, and idiomatic slicing, each of which reduces the number of constant periods over which the query is evaluated.
We also extend a conventional XML query benchmark to effect a temporal XML query benchmark. Experiments on this benchmark show that in-place slicing is the best. We then apply the approaches used in tauXQuery to temporal SQL/PSM. The stratum architecture and some of the time-slicing techniques work for temporal SQL/PSM. Empirical comparison is performed by running a variety of temporal queries.