An algebraic approach for incremental maintenance of materialized XQuery views

Abstract

XML has become an important medium for representing and exchanging data over the Internet. Data sources, including structural and semi-structural sources, often export XML views over base data, and then materialize the view by storing its XML query result to provide faster data access. Upon change to the base data, it is typically more efficient to maintain a view by incrementally propagating the delta changes to the view than by re-computing it from scratch. Techniques for the incremental maintenance of relational views have been extensively studied in the literature. However, the maintenance of views created using XQuery is as of now unexplored. In this paper we propose an algebraic approach for incremental XQuery view maintenance. In our approach, an update to the XML source is transformed into a set of well defined update primitives which are propagated through the XML algebra tree. This algebraic update propagation process generates incremental update primitives to be applied to the result view. Our update propagation strategy based on the XAT XML algebra and the propagation rules for individual algebra operators are given. We briefly discuss our XQuery view maintenance system implementation, and present our experiments that confirm that incremental view maintenance is indeed faster than re-computation.

Triggers over nested views of relational data

“…This problem is similar to the problem of incremental view maintenance in relational/nested-relational/objectoriented/semistructured databases [Abiteboul et al 1998;Dimitrova et al 2003;El-Sayed et al 2002;Ceri and Widom 1991;Griffin and Libkin 1995;Gupta and Mumick 1995;Papakonstantinou et al 1995;Abiteboul et al 1997]. In fact, we do reuse some algorithms from the view maintenance literature Widom 1990, 1991] to determine which updates on the base data can cause updates to the view.…”

“…We avoid materialization because (a) it would require a sophisticated middleware database that can support incremental view updates and triggers over nested views, and (b) it would require the view to be updated for every relevant relational update even though user triggers may have very selective predicates. 1 In contrast, most incremental view maintenance algorithms (e.g., Abiteboul et al [1998], Bohannon et al [2004], Ceri and Widom [1991], Dimitrova et al [2003], El-Sayed et al [2002], Gluche et al [1997], Kawaguchi et al [1997], Kuno and Rundensteiner [1998], and Rys et al [1996]) assume that the view is materialized, and use the materialized old value of a row to compute its new value. We thus need to devise techniques that can selectively compute the relevant new values directly from the base data.…”

Incremental maintenance of aggregate and outerjoin expressions

“…A large body of work exists describing different algorithms for incrementally maintaining materialized views [4][5][6][7][8][9][10][11][12][13][23][24][25][26][27][28][29][30]. Each work applies to different classes of views and has various advantages and disadvantages.…”

“…Liu and Vincent in [27,28] derive incremental expressions for the general nested relational model which is used in warehouses and in XML data. El-Sayed et al in [29,30] present an algebraic approach for incremental maintenance of materialized views expressed in XQuery, an XML query language.…”

Generating rules for incremental maintenance of XML view of relational data

“…In the re-materialization strategy, view data is re-computed at preestablished times. In the incremental maintenance strategy, a mechanism periodically modifies view data to reflect updates to local sources, which proved to be an effective solution [1,5].…”