Lossless Conditional Schema Evolution

Ole Guttorm Jensen, Michael Hanspeter Bøhlen

Research output: Working paperResearch

Abstract

The paper considers conditional schema evolution, where schema changes change the schema of the tuples that satisfy the change condition. When the schema of a relation change some tuples may no longer fit the current schema. Handling the mismatch between the intended schema of tuples and the recorded schema of tuples is at the core of a DBMS that supports schema evolution. We propose to keep track of schema mismatches at the level of individual tuples, and prove that conditionally evolving schemas, in contrast to current commercial database systems, are lossless when the schema evolves. The lossless property is a precondition for a flexible semantics that allows to correctly answer general queries over evolving schemas. The key challenge is to handle attribute mismatches between the intended and recorded schema in a consistent way. We provide a parametric approach to resolve mismatches according to the needs of the application. We introduce the mismatch extended completed schema (MECS) which records attributes along with their mismatches, and we prove that relations with MECS are lossless. Finally, we provide parametric mismatch resolution for relations with MECS, and establish an upper bound on its time complexity
Original languageEnglish
Pages21
Publication statusPublished - 2003

Keywords

  • Schema Evolution

Cite this

Jensen, O. G., & Bøhlen, M. H. (2003). Lossless Conditional Schema Evolution. (pp. 21).
Jensen, Ole Guttorm ; Bøhlen, Michael Hanspeter. / Lossless Conditional Schema Evolution. 2003. pp. 21
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Jensen, OG & Bøhlen, MH 2003 'Lossless Conditional Schema Evolution' pp. 21.

Lossless Conditional Schema Evolution. / Jensen, Ole Guttorm; Bøhlen, Michael Hanspeter.

2003. p. 21.

Research output: Working paperResearch

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AB - The paper considers conditional schema evolution, where schema changes change the schema of the tuples that satisfy the change condition. When the schema of a relation change some tuples may no longer fit the current schema. Handling the mismatch between the intended schema of tuples and the recorded schema of tuples is at the core of a DBMS that supports schema evolution. We propose to keep track of schema mismatches at the level of individual tuples, and prove that conditionally evolving schemas, in contrast to current commercial database systems, are lossless when the schema evolves. The lossless property is a precondition for a flexible semantics that allows to correctly answer general queries over evolving schemas. The key challenge is to handle attribute mismatches between the intended and recorded schema in a consistent way. We provide a parametric approach to resolve mismatches according to the needs of the application. We introduce the mismatch extended completed schema (MECS) which records attributes along with their mismatches, and we prove that relations with MECS are lossless. Finally, we provide parametric mismatch resolution for relations with MECS, and establish an upper bound on its time complexity

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Jensen OG, Bøhlen MH. Lossless Conditional Schema Evolution. 2003, p. 21.