Document Type

Other

Publication Date

7-1999

Abstract

Data warehouses (DW) are an emerging technology to support high-level decision making by gathering information from several distributed information sources (ISs) into one repository. In dynamic environments such as the web, DWs must be maintained in order to stay up-to-date. Recently proposed view maintenance algorithms tackle this problem of DW management under concurrent data updates (DU) at different ISs, whereas the EVE system is the first to handle non-concurrent schema changes (SC) of ISs. However, the concurrency of schema changes by different ISs as well as the concurrency of both interleaved schema changes (SC) and data updates (DU) still remain unexplored problems.

In this paper, we propose a solution framework called DyDa that successfully addresses both problems. The DyDa framework detects concurrent SCs by the broken query scheme and conflicting concurrent DUs by a local timestamp scheme. A fundamental idea of the DyDa framework is the development of a two-layered architecture that separates the concerns for concurrent DU and concurrent SC handling without imposing any restrictions on the fully concurrent execution of the ISs. At the lower (query engine) level of the framework, it employs a local correction algorithm to handle concurrent DUs, and a local name mapping strategy to handle concurrent rename-SCs that rename either attributes or relations at the IS space. At the higher (DW management) level, it addresses the problem of concurrent (drop-SC) operations that drop attributes ore relations from the IS space. For the later, the view synchronization (VS) algorithm is modified to keep track of view evolution information as needed for handling sequences of concurrent SCs. We also design a new view adaption (VA) algorithm, called Map-VA, that incrementally adapts the view extent for a modified view definition even under interleaved SCs and DUs. Put together, these algorithms provide a comprehensive solution to DW management under concurrent SCs and DUs. This solution is currently being implemented within the EVE data warehousing system.

DOI

WPI-CS-TR-99-20

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