Bridging relational database history and the web: The XML approach

The preservation of digital artifacts represents an unanswered challenge for the modern information society: XML and its query languages provide an effective environment to address this challenge because of their ability to support temporal information and queries, and make it easy to publish database history to the Web. In this paper, we focus on the problem of preserving, publishing, and querying efficiently the history of a relational database. Past research on temporal databases revealed the difficulty of achieving satisfactory solutions using flat relational tables and SQL. Here we show that the problem can be solved using (a) XML to support temporally grouped representations of the database history, and (b) XQuery to express powerful temporal queries on such representations. Furthermore, the approach is quite general and it can be used to preserve and query the history of multi-version XML documents. Then we turn to the problem of efficient implementation, and we investigate alternative approaches, including (i) XML DBMS, (ii) shredding XML into relational tables and using SQL/XML on these tables, (iii) SQL:2003 nested tables, and iv) OR-DBMS extended with XML support. These experiments suggest that a combination of temporal XML views and physical relational tables provides the best approach for managing temporal database information.