ABSTRACT
A schema mapping is a specification that describes how data from a source schema is to be mapped to a target schema. Once the data has been transferred from the source to the target, a natural question is whether one can undo the process and recover the initial data, or at least part of it. In fact, it would be desirable to find a reverse schema mapping from target to source that specifies how to bring the exchanged data back.
In this paper, we introduce the notion of a recovery of a schema mapping: it is a reverse mapping M' for a mapping M that recovers sound data with respect to M. We further introduce an order relation on recoveries. This allows us to choose mappings that recover the maximum amount of sound information. We call such mappings maximum recoveries. We study maximum recoveries in detail, providing a necessary and sufficient condition for their existence. In particular, we prove that maximum recoveries exist for the class of mappings specified by FO-to-CQ source-to-target dependencies. This class subsumes the class of source-to-target tuple-generating dependencies used in previous work on data exchange. For the class of mappings specified by FO-to-CQ dependencies, we provide an exponential-time algorithm for computing maximum recoveries, and a simplified version for full dependencies that works in quadratic time. We also characterize the language needed to express maximum recoveries, and we include a detailed comparison with the notion of inverse (and quasi-inverse) mapping previously proposed in the data exchange literature. In particular, we show that maximum recoveries strictly generalize inverses. We study the complexity of some decision problems related to the notions of recovery and maximum recovery. Finally, we report our initial results about a relaxed
notion of maximal recovery, showing that it strictly generalizes the notion of maximum recovery.
- F. Afrati, C. Li, and V. Pavlaki. Data exchange with arithmetic comparisons. Technical report, UCI ICS, 2006.Google Scholar
- M. Arenas, P. Barceló, R. Fagin, and L. Libkin. Locally consistent transformations and query answering in data exchange. In PODS, pages 229--240, 2004. Google Scholar
Digital Library
- P. Bernstein. Applying model management to classical meta data problems. In CIDR, 2003.Google Scholar
- P. Bernstein and S. Melnik. Model management 2.0: manipulating richer mappings. In SIGMOD, pages 1--12, 2007. Google Scholar
Digital Library
- A. Deutsch and V. Tannen. Reformulation of XML queries and constraints. In ICDT, pages 225--241, 2003. Google Scholar
Digital Library
- R. Fagin. Horn clauses and database dependencies. JACM, 29(4):952--985, 1982. Google Scholar
Digital Library
- R. Fagin. Inverting schema mappings. TODS, 32(4), 2007. Google Scholar
Digital Library
- R. Fagin, P. G. Kolaitis, R. J. Miller, and L. Popa. Data exchange: semantics and query answering. TCS, 336(1):89--124, 2005. Google Scholar
Digital Library
- R. Fagin, P. G. Kolaitis, L. Popa, and W.-C. Tan. Composing schema mappings: second-order dependencies to the rescue. TODS, 30(4):994--1055, 2005. Google Scholar
Digital Library
- R. Fagin, P. G. Kolaitis, L. Popa, and W.-C. Tan. Quasi-inverses of schema mappings. In PODS, pages 123--132, 2007. Google Scholar
Digital Library
- G. De Giacomo, D. Lembo, M. Lenzerini, and R. Rosati. On reconciling data exchange, data integration, and peer data management. In PODS, pages 133--142, 2007. Google Scholar
Digital Library
- G. Gottlob and A. Nash. Data exchange: computing cores in polynomial time. In PODS, pages 40--49, 2006. Google Scholar
Digital Library
- P. G. Kolaitis, J. Panttaja, and W.-C. Tan. The complexity of data exchange. In PODS, pages 30--39, 2006. Google Scholar
Digital Library
- L. Libkin. Data exchange and incomplete information. In PODS, pages 60--69, 2006. Google Scholar
Digital Library
- S. Melnik. Generic Model Management: Concepts and Algorithms, volume 2967 of LNCS. Springer, 2004. Google Scholar
Digital Library
- S. Melnik, P. Bernstein, A. Y. Halevy, and E. Rahm. Supporting executable mappings in model management. In SIGMOD, pages 167--178, 2005. Google Scholar
Digital Library
Index Terms
The recovery of a schema mapping: bringing exchanged data back
Recommendations
The recovery of a schema mapping: Bringing exchanged data back
A schema mapping is a specification that describes how data from a source schema is to be mapped to a target schema. Once the data has been transferred from the source to the target, a natural question is whether one can undo the process and recover the ...
Quasi-inverses of schema mappings
Schema mappings are high-level specifications that describe the relationship between two database schemas. Two operators on schema mappings, namely the composition operator and the inverse operator, are regarded as especially important. Progress on the ...
Quasi-inverses of schema mappings
PODS '07: Proceedings of the twenty-sixth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systemsSchema mappings are high-level specifications that describe the relationship between two database schemas. Two operators on schema mappings, namely the composition operator and the inverse operator, are regarded as especially important. Progress on the ...






Comments