Abstract
Users today are struggling to integrate a broad range of information sources providing different levels of query capabilities. Currently, data sources with different and limited capabilities are accessed either by writing rich functional wrappers for the more primitive sources, or by dealing with all sources at a “lowest common denominator”. This paper explores a third approach, in which a mediator ensures that sources receive queries they can handle, while still taking advantage of all of the query power of the source. We propose an architecture that enables this, and identify a key component of that architecture, the Capabilities-Based Rewriter (CBR). The CBR takes as input a description of the capabilities of a data source, and a query targeted for that data source. From these, the CBR determines component queries to be sent to the sources, commensurate with their abilities, and computes a plan for combining their results using joins, unions, selections, and projections. We provide a language to describe the query capability of data sources and a plan generation algorithm. Our description language and plan generation algorithm are schema independent and handle SPJ queries. We also extend CBR with a cost-based optimizer. The net effect is that we prune without losing completeness. Finally we compare the implementation of a CBR for the Garlic project with the algorithms proposed in this paper.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
R. Ahmed et al. The Pegasus heterogeneous multidatabase system. IEEE Computer, 24:19-27, 1991.
M.J. Carey et al. Towards heterogeneous multimedia information systems: The Garlic approach. In Proc. RIDE-DOM Workshop, pages 124-31, 1995.
R. Fagin. Combining fuzzy information from multiple systems. In Proc. PODS, 1996.
J.C. Franchitti and R. King. Amalgame: a tool for creating interoperating persistent, heterogeneous components. Advanced Database Systems, pages 313-36, 1993.
P. Gassner, G. Lohman, B. Schiefer, and Y. Wang. Query optimization in the IBM DB2 family. IEEE Data Engineering Bulletin, 16:4-18, September 1993.
A. Gupta. Integration of Information Systems: Bridging Heterogeneous Databases. IEEE Press, 1989.
L. Haas, D. Kossman, E. Wimmers, and J. Yang. Optimizing queries across diverse data sources. In Proc. VLDB, 1997.
J. Hammer and D. McLeod. An approach to resolving semantic heterogeneity in a federation of autonomous, heterogeneous database systems. Intl Journal of Intelligent and Cooperative information Systems, 2:51-83, 1993.
A. Levy, A. Mendelzon, Y. Sagiv, and D. Srivastava. Answering queries using views. In Proc. PODS Conf., pages 95-104, 1995.
G. Lohman. Grammar-like functional rules for representing query optimization alternatives. In Proc. ACM SIGMOD, 1988.
A. Levy, A. Rajaraman, and J. Ordille. Query processing in the information manifold. In Proc. VLDB, 1996.
A. Levy, A. Rajaraman, and J. Ullman. Answering queries using limited external processors. In Proc. PODS, pages 227-37, 1996.
P.A. Larson and H.Z. Yang. Computing queries from derived relations. In Proc. VLDB Conf., pages 259-69, 1985.
Y. Papakonstantinou, A. Gupta, H. Garcia-Molina, and J. Ullman. A query translation scheme for the rapid implementation of wrappers. In Proc. DOOD Conf., pages 161-86, 1995.
Y. Papakonstantinou, A. Gupta, and L. Haas. Capabilities-based query rewriting in mediator systems. In Proc. PDIS, 1996.
Y. Papakonstantinou, H. Garcia-Molina, and J. Widom. Object exchange across heterogeneous information sources. In Proc. ICDE Conf., pages 251-60, 1995.
Xiaolei Qian. Query folding. In Proc. ICDE, pages 48-55, 1996.
A. Rajaraman, Y. Sagiv, and J. Ullman. Answering queries using templates with binding patterns. In Proc. PODS Conf., pages 105-112, 1995.
V.S. Subrahmanian et al. HERMES: A heterogeneous reasoning and mediator system. http://www.cs.umd.edu/projects/hermes/overview/paper.
P. Selinger, M. Astrahan, D. Chamberlin, R. Lorie, and T. Price. Access path selection in a relational database management system. In Proc. ACM SIGMOD, 1979.
S. Sagiv and M. Yannakakis. Equivalences among relational expressions with the union and difference operators. JACM, 27:633-55, 1980.
A. Tomasic, L. Raschid, and P. Valduriez. Scaling heterogeneous databases and the design of DISCO. Technical report, INRIA, 1995.
J.D. Ullman. Principles of Database and Knowledge-Base Systems, Vol. I: Classical Database Systems. Computer Science Press, New York, NY, 1988.
J.D. Ullman. Principles of Database and Knowledge-Base Systems,Vol. II: The NewTechnologies. Computer Science Press, New York, NY, 1989.
V. Vassalos and Y. Papakonstantinou. Describing and using query capabilities of heterogeneous sources. Available via http://www-cse.ucsd.edu/ yannis/.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Papakonstantinou, Y., Gupta, A. & Haas, L. Capabilities-Based Query Rewriting in Mediator Systems. Distributed and Parallel Databases 6, 73–110 (1998). https://doi.org/10.1023/A:1008646830769
Issue Date:
DOI: https://doi.org/10.1023/A:1008646830769