Incremental View Maintenance For Collection Programming

In the context of incremental view maintenance (IVM), delta query derivation is an essential technique for speeding up the processing of large, dynamic datasets. The goal is to generate delta queries that, given a small change in the input, can update the materialized view more efficiently than via recomputation. In this work we propose the first solution for the efficient incrementalization of positive nested relational calculus (NRC+) on bags (with integer multiplicities). More precisely, we model the cost of NRC+ operators and classify queries as efficiently incrementalizable if their delta has a strictly lower cost than full re-evaluation. Then, we identify IncNRC+; a large fragment of NRC+ that is efficiently incrementalizable and we provide a semantics-preserving translation that takes any NRC+ query to a collection of IncNRC+ queries. Furthermore, we prove that incremental maintenance for NRC+ is within the complexity class NC0 and we showcase how recursive IVM, a technique that has provided significant speedups over traditional IVM in the case of flat queries [25], can also be applied to IncNRC+.Comment: 24 pages (12 pages plus appendix

Order-sensitive view maintenance of materialized xquery views

Materialized XML views are a popular technique for integrating data from possibly dis-tributed and heterogeneous data sources. However, the problem of the incremental main-tenance of such XML views poses new challenges which to date remain unaddressed. One, XML views not only filter the data, but may radically restructure it to construct new XML nested document structures. Moreover, order is inherent in the XML model, and XML views reflect both the implicit document order of the underlying sources and the order explicitly imposed in the view definition. Therefore, order also has to be preserved at view maintenance time. In this thesis we present an algebraic approach for the incremental maintenance of XQuery views, called VOX (View maintenance for Ordered XML). To the best of our knowledge, this is the first solution to order-preserving XML view maintenance. Our strategy correctly transforms an update to source XML data into sequences of updates that refresh the view. Our technique is based on an algebraic representation of the XQuery view expression using an XML algebra. The XML algebra has ordered bag semantics

Abstract Efficiently Supporting Order in XML Query Processing

XML is an ordered data model and XQuery expressions return results that have a welldefined order. However, little work on how order is supported in XML query processing has been done to date. In this paper we study the issues related to handling order in the XML context, namely challenges imposed by the XML data model, the variety of order requirements of the XQuery language, and the need to maintain order in the presence of updates to the XML data. We propose an efficient solution that addresses all these issues. Our solution is based on a key encoding for XML nodes that serves as node identity and at the same time encodes order. We design rules for encoding order of processed XML nodes based on the XML algebraic query execution model and the node key encoding. These rules do not require any actual sorting for intermediate results during execution. Our approach enables efficient order-sensitive incremental view maintenance as it makes most XML algebra operators distributive with respect to bag union. We prove the correctness of our order encoding approach. Our approach is implemented and integrated with Rainbow, an XML data management system developed at WPI. We have tested the efficiency of our approach using queries that have different order requirements. We have also measured the relative cost of different components related to our order solution in different types of queries. In general the overhead of maintaining order in our approach is very small relative to the query processing time