10. A system for creating a data mart in a business intelligence server environment on a computer including one or more microprocessors, said system comprising: a plurality of data sources that maintain data within an enterprise, said plurality of data sources including at least a relational database and a multidimensional database; a business intelligence server, executing on the computer, that provides a virtual logical semantic model, wherein the virtual logical semantic model is a presentation layer to a user and is logically mapped to a plurality of physical models, each said physical model representing entities in a said data source, wherein the business intelligence server receives a specification of a list of levels and a selection of a said data source for storing aggregated data by using the virtual logical semantic model, wherein the plurality of levels spans data from at least two of said plurality of data sources, wherein said levels are identified by analyzing runtimes of queries on the two or more said data sources, wherein at least one said query reduces runtimes thereof by aggregating the data at said levels; an aggregate matrix, created with the virtual semantic model, which includes the plurality of levels, wherein the aggregate matrix is operable to perform data aggregation only at said levels by creating for each said level, in the said data source, a single aggregate table that contains columns at the each said level and at higher levels in a dimension hierarchy, and creating for each fact table a single aggregate table that includes columns corresponding to primary keys at the each said level; wherein the business intelligence server generates a multidimensional cube that contains the aggregated data in the aggregate tables, and stores the multidimensional cube in the said data source.
10. A system for creating a data mart in a business intelligence server environment on a computer including one or more microprocessors, said system comprising: a plurality of data sources that maintain data within an enterprise, said plurality of data sources including at least a relational database and a multidimensional database; a business intelligence server, executing on the computer, that provides a virtual logical semantic model, wherein the virtual logical semantic model is a presentation layer to a user and is logically mapped to a plurality of physical models, each said physical model representing entities in a said data source, wherein the business intelligence server receives a specification of a list of levels and a selection of a said data source for storing aggregated data by using the virtual logical semantic model, wherein the plurality of levels spans data from at least two of said plurality of data sources, wherein said levels are identified by analyzing runtimes of queries on the two or more said data sources, wherein at least one said query reduces runtimes thereof by aggregating the data at said levels; an aggregate matrix, created with the virtual semantic model, which includes the plurality of levels, wherein the aggregate matrix is operable to perform data aggregation only at said levels by creating for each said level, in the said data source, a single aggregate table that contains columns at the each said level and at higher levels in a dimension hierarchy, and creating for each fact table a single aggregate table that includes columns corresponding to primary keys at the each said level; wherein the business intelligence server generates a multidimensional cube that contains the aggregated data in the aggregate tables, and stores the multidimensional cube in the said data source. 15. The system of claim 10 , wherein the plurality of data sources further include at least one of an Oracle database, an Oracle Essbase database and an Oracle Analytic Workspace.