Version management and historical queries in digital libraries

Historical information can be effectively preserved using XML and searched through powerful historical queries written in XQuery. Indeed, by storing the successive versions of a document in an incremental fashion, XML repositories and data warehouses can achieve (i) the efficient preservation of critical information, (ii) its representation using a temporally grouped data model and (iii) the ability of supporting historical queries on the evolution of documents and their contents using XQuery. The proposed approach can be applied uniformly to (a) XML document archives and (b) transaction time databases published in XML and queried in XQuery. Our case studies include the UCLA course catalog, W3C Xlink standards, and the CIA WorldFact Book, besides relational databases. The experience described here and in the work of Wang et al. (2005 and 2003) suggests that current standards provide reasonable support for temporal applications at the logical level, whereas many challenges remain at the physical level.