1. A method for establishing a mapping between internal metadata for a database and external metadata, 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 the internal metadata to be mapped to the external metadata; in response to receiving the user selection: determining if the external metadata describing all data points within said selection is predefined, and if so, receiving from said user a definition of external metadata comprising: presenting said user a list from which they may select an item of predefined metadata; and receiving from said user a selection of an item of predefined metadata from said list; and determining if a syntax of the external metadata describing all data points within said selection is predefined and the external metadata for said selection is not predefined, and if so, receiving from said user a definition of external metadata comprising: presenting said user with one or more dialog boxes in which they can specify external metadata to be created; and receiving from said user a specification of external metadata to be created; and determining if neither the external metadata describing all data points within said selection is predefined nor the syntax of the external metadata describing all data points within said selection is predefined, and if so creating new internal metadata comprising: creating a new row or column in the grid; receiving a formula involving the user selection of a portion of the grid; entering the formula into a cell in the new row or column; and repeating the steps of determining if the external metadata describing all data points within said selection is predefined and determining if a syntax of the external metadata describing all data points within said selection is predefined; and creating a mapping between the internal metadata of the selected portion of the grid and the external metadata based on the user selections.