Schema mapping system and method
First Claim
1. An apparatus for implementing a database query system, the apparatus comprising:
- a processor for executing instructions; and
a memory device having thereon modules of executable and operational data for execution by the processor, the modules comprising;
a schema mapping module executable on a processor to express a schema mapping between a plurality of database schemas, the database schemas containing at least partially replicated information; and
a middleware module adapted to employ a middleware schema for use as a reference by the schema mapping module in expressing the schema mapping.
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Abstract
A schema mapping system and method are particularly suitable for expressing a schema mapping between two database schemas that may be heterogeneous (restructuring views of each other). The schema mapping system is useful for generating a least cost query plan expressible on a plurality of heterogeneous tables that are restructuring views of each other. The system may be configured to receive a query against one of the tables and convert it to a plurality of alternate queries, each formatted for the particular schema of a different one of the plurality of heterogeneous tables. In generating the alternate queries, the schema mapping system may utilize SchemaSQL view definitions and may employ restructuring operators expressing and capable of conducting a restructuring of a table into a restructuring view of the table. The system may employ a canonical schema and a virtual canonical table to express a mapping between restructuring views, and may utilize the schema mapping for purposes of query conversion. The alternate queries may be costed and optimized and a query plan returned that has a least cost or service time involved.
130 Citations
30 Claims
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1. An apparatus for implementing a database query system, the apparatus comprising:
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a processor for executing instructions; and
a memory device having thereon modules of executable and operational data for execution by the processor, the modules comprising;
a schema mapping module executable on a processor to express a schema mapping between a plurality of database schemas, the database schemas containing at least partially replicated information; and
a middleware module adapted to employ a middleware schema for use as a reference by the schema mapping module in expressing the schema mapping. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
a query translation module executable on a processor to communicate with the schema mapping module and translate a query executable on one of the plurality of database schemas to equivalent queries on others of the plurality of database schemas; and
a costing module executable on the processor to select from among the equivalent queries a query corresponding to a selected criterion.
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11. A method for implementing a database query system, the method comprising:
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expressing a schema mapping between a plurality of database schemas, the database schemas containing at least partially replicated information; and
referencing a middleware schema in expressing the schema mapping. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
automatically translating a query executable on one of the plurality of database schemas to equivalent queries on others of the plurality of database schemas; and
automatically selecting from among the equivalent queries a query corresponding to a selected criterion.
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21. An article of manufacture comprising a program storage medium readable by a processor and embodying one or more instructions executable by the processor to perform a method for implementing a database query system, the method comprising:
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expressing a schema mapping between a plurality of database schemas, the database schemas containing at least partially replicated information; and
referencing a middleware schema in expressing the schema mapping. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30)
automatically translating a query executable on one of the plurality of database schemas to equivalent queries on others of the plurality of database schemas; and
automatically selecting from among the equivalent queries a query corresponding to a selected criterion.
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Specification