10. A computer-implemented method of processing an abstract query that includes a group of logical fields specified by a field-to-field join constraint, comprising, by operation of a least one processor: receiving, the abstract query from a requesting entity having an interface in which the abstract query was composed, wherein the abstract query is composed from a plurality of logical fields specified in a database abstraction model, and wherein each logical field defines at least an access method that maps the logical field to data in an underlying physical database; generating, from the abstract query, a resolved query of the underlying physical database; the generating being performed by a runtime component; modifying the resolved query according to the field-to-field join constraint, wherein the field-to-field join constraint defines how the set of query results retrieved for the group of logical fields should be joined together for purposes of being output; executing the resolved query to retrieve a set of grouped query results from the database; and returning the grouped query results to the requesting entity.
10. A computer-implemented method of processing an abstract query that includes a group of logical fields specified by a field-to-field join constraint, comprising, by operation of a least one processor: receiving, the abstract query from a requesting entity having an interface in which the abstract query was composed, wherein the abstract query is composed from a plurality of logical fields specified in a database abstraction model, and wherein each logical field defines at least an access method that maps the logical field to data in an underlying physical database; generating, from the abstract query, a resolved query of the underlying physical database; the generating being performed by a runtime component; modifying the resolved query according to the field-to-field join constraint, wherein the field-to-field join constraint defines how the set of query results retrieved for the group of logical fields should be joined together for purposes of being output; executing the resolved query to retrieve a set of grouped query results from the database; and returning the grouped query results to the requesting entity. 11. The method of claim 10 , wherein the set of query results are grouped into one of (i) instances of a set, wherein the field-to-field join constraint includes an instance indicator used to determine which instance of a set that an element of data included in the query results is placed or (ii) an ordered series, wherein an instance identifier is used to determine the order, relative to the series, of an element of data from the query results.