Achieving adaptivity for OLAP-XML federations

Abstract

Motivated by the need for more flexible OLAP systems, this paper presents work on logical integration of external data in OLAP databases, carried out in cooperation between the Danish OLAP client vendor TARGIT and Aalborg University. Flexibility is ensured by supporting XML as the external data format, since almost all data sources can be efficiently wrapped in XML. Earlier work has resulted in an extension of the TARGIT system, allowing external XML data to be used as dimensions and measures in OLAP databases. This work has led to a number of new ideas for improving the system's ability to adapt to changes in its surroundings.This paper describes the potential problems that may interrupt the operation of the integration system, in particular those caused by the often autonomous and unreliable nature of external XML data sources, and methods for handling these problems. Specifically, we describe techniques for handling changes in external XML data sources. We also describe techniques for improving the reliability of external XML sources, e.g., when these are found on the Internet, by dynamically trying to locate alternative sources during the evaluation of a query. Finally, we discuss solutions to a number of other possible problems, and show how the techniques can be integrated in the TARGIT architecture. Experiments performed with a prototype implementation of central functionality shows the viability of the proposed solutions.

Finding an application-appropriate model for XML data warehouses

“…This is called ''decorating'' the dimension with additional information coming from XML sources. Complementary to this approach, in [54], the same authors consider handling changes in the XML document sources.…”

Cubing Algorithms for XML Data

“…Cost model and estimation of SQL XM query trees are provided by the same authors in [25], whereas in [26] the same authors again focus the attention on query optimization techniques for SQL XM query trees. Still in line with this main research direction, [22] studies the problem of enriching SQL XM by novel characteristics that allow us to achieve adaptive features during query and processing tasks over OLAP-XML federations, with the aim of making SQL XM robust with respect to changes that can occur in external XML data sources, and compliant with load balancing issues over external XML data sources. Furthermore, in [23] authors extend previous research results by devising an interesting case study focused on OLAP-XML federations in the context of the OLAP server platform TARGIT, and show how external Web-accessible XML data can be integrated within a real-life OLAP server platform thanks to ad-hoc constructs, data models and query languages.…”

Integrating Data Warehouses with Web Data: A Survey

“…In [53], an adaptive query processing technique for federated database environments was proposed. Finally, [54] and [55] consider adaptivity in a federation of XML and OLAP data sources (see Section 5.3).…”