1. A computer-readable storage medium containing a program, which when executed on a computer system performs an operation for providing access to physical data in a physical database, comprising: (i) providing a physical data field layer that provides a plurality of physical data fields, wherein each physical data field specifies a mapping from the physical data field to a data location in the physical database; (ii) providing a logical field layer that includes a plurality of logical field definitions, each of the definitions comprising a logical field name and a reference to an access method that defines a manner of exposing specified data specified data for the logical field definition, wherein each physical data field, of the plurality of physical data fields, is initially generated based on one of the logical field definitions included in the logical field layer by: identifying the access method defined for a particular logical field definition, generating a corresponding physical data field that maps to a data location of the specified data, and redefining the access method for the particular logical field definition to expose data retrieved from the corresponding physical data field; and (iii) providing an interface to the plurality of logical field definitions, wherein the interface presents a user with an interface for composing an abstract query from the logical field definitions.