Apparatus and method for utilizing context to resolve ambiguous queries
A computer readable storage medium includes executable instructions to derive from a database schema an irreducible ambiguous group comprising a sub-schema with a set of vertices wherein any two vertices are part of a loop. Contexts are defined on the sub-schema. For each context, joins in the sub-schema are designated as mandatory joins, excluded joins and neutral joins. A selection of a context from multiple contexts invoked by a path characterizing a query is processed. The query is resolved using the context.
1. A non-transitory computer readable storage medium, comprising executable instructions causing at least one computing system to:
derive, from a database schema, an irreducible ambiguous group comprising a sub-schema with a set of vertices wherein any two vertices are part of a loop and have at least two minimal paths relating them in the sub-schema, the sub-schema specifying a subset of a graph of the database schema and comprising a list of boundary tables and a list of object tables, the boundary tables connecting the sub-schema to other parts of the database schema, the object tables being used to define objects in a semantic layer;
receive user generated input designating joins in the sub-schema as excluded joins; and
define a context of the sub-schema by: finding a tree that connects all boundary tables of the sub-schema plus all of the object tables of the sub-schema while excluding the excluded joins the tree specifying mandatory joins and neutral joins.
2. The computer readable storage medium of claim 1 further comprising executable instructions to resolve a query using the context, wherein the context associates at least two tables specified by the query.
3. The computer readable storage medium of claim 2 further comprising executable instructions to process a selection of a context from multiple contexts invoked by a path characterizing the query.
4. The computer readable storage medium of claim 2 further comprising executable instructions to remove sub-schema joins that are excluded joins.
5. The computer readable storage medium of claim 2 further comprising executable instructions to remove any context with mandatory joins excluded by a selected element.
6. The computer readable storage medium of claim 1 further comprising executable instructions to form one context per fact table.
7. The computer readable storage medium of claim 1 further comprising executable instructions to build a list of irreducible ambiguous groups, each irreducible ambiguous group specifying a list of contained tables, the list of boundary tables, and a collapsed table associated with the irreducible ambiguous group.
8. The computer readable storage medium of claim 1 further comprising executable instructions to form a nested context.
9. The computer readable storage medium of claim 1 wherein the sub-schema includes at least one contained table, at least one boundary table and at least one collapsed table.
10. A method for implementation by at one or more data processors comprising:
deriving, by at least one data processor from a database schema, a sub-schema with a set of vertices wherein any two vertices are part of a loop and have at least two minimal paths relating them in the sub-schema, the sub-schema specifying a subset of a graph of the database schema and comprising a list of boundary tables and a list of object tables, the boundary tables connecting the sub-schema to other parts of the database schema, the object tables being used to define objects in a semantic layer;
receiving, by at least one data processor, data designating joins in the sub-schema as excluded joins; and
defining, by at least one data processor, a context for the sub-schema by finding a tree that connects all boundary tables of the sub-schema plus all of the object tables of the sub-schema while excluding the excluded joins, the tree specifying mandatory joins and neutral joins.
11. A system comprising:
at least one data processor;
memory coupled to the at least one data processor, the memory storing instructions, which when executed, cause the at least one data processor to:
derive, from a database schema, a sub-schema with a set of vertices wherein any two vertices are part of a loop and have at least two minimal paths relating them in the sub-schema, the sub-schema specifying a subset of a graph of the database schema and comprising a list of boundary tables and a list of object tables, the boundary tables connecting the sub-schema to other parts of the database schema, the object tables being used to define objects in a semantic layer;
receive data designating joins in the sub-schema as excluded joins; and
define a context for the sub-schema by finding a tree that connects all boundary tables of the sub-schema plus all of the object tables of the sub-schema while excluding the excluded joins, the tree specifying mandatory joins and neutral joins.