A method and apparatus for defining and processing aggregate data is disclosed. Using database abstraction techniques, a set of logical fields may be used to compose queries of a set of underlying physical data sources. In one embodiment, a logical field may represent an aggregate data value calculated from the elements appearing in a column of a relational table in an underlying physical data source. The elements may be divided into to subsets to calculate multiple aggregate values. An abstract derived entity is a data object present in a database abstraction model that may be accessed as though it were a relational table contained in an underlying physical data source. In one embodiment, columns of the table defined by the abstract derived entity may be populated with aggregate data values joined to other data as specified by a composition rule included in the definition of the abstract derived entity.