1. A method for establishing a mapping between internal metadata for a database and external metadata for a report, the method comprising: reading the internal metadata from the database, the internal metadata including metadata that describes data stored in the database; generating and displaying a screen, the screen including a grid having rows and columns, the rows and columns having dimensional metadata from the internal metadata placed in the grid as row and/or column headings the grid further including the internal metadata read from the database; receiving from a user a selection of a portion of the grid, the selection indicating one or more cells of the grid; in response to receiving the user selection: determining the internal metadata displayed on the grid that corresponds to the one or more cells, the internal metadata corresponding to the one or more cells forming a subset of the internal metadata displayed on the grid, wherein the user modifies the internal metadata to indicate the internal metadata is to be mapped to external metadata; presenting to the user one or more user interface controls for receiving a definition of external metadata for the subset of the internal metadata, the definition of external metadata specifying particular associations of the subset of internal metadata with the external metadata in the report, the definition describing all data points within the user selection; receiving via the one or more user interface controls, the definition of external metadata from the user, and based on the definition of the external metadata, creating a first mapping between the selected internal metadata and the external metadata; generating a report definition for the report, the report definition describing how report data described by the external metadata in the report is to be produced from the data stored in the database and described by the internal metadata; and storing the report definition, the report definition including the first mapping of internal metadata to external metadata for the report, wherein the first mapping applies only to a particular report and does not create a persistent association of the internal metadata with the external metadata such that a second report may be defined which uses a second mapping of the internal metadata to the external metadata, said second mapping being different from the first mapping, said second mapping associated with said second report.