1. A computer-implemented method of creating a database abstraction model, comprising, by operation of a least one processor: defining a database abstraction model, wherein the database abstraction model defines a plurality of logical fields for composing abstract queries via an interface, wherein each logical field specifies (i) a name for the logical field and (ii) at least an access method that maps the logical field to data in an underlying physical database; defining, for the database abstraction model, a field-to-field join constraint based on an identified logical relationship for a group of logical fields, wherein the field-to-field join constraint defines how a set of query results retrieved for the group of logical fields should be joined together for purposes of being output; wherein an abstract query composed via the interface and including the group of logical fields is a format suitable to be transformed by a runtime component into a resolved query of the database; and storing the database abstraction model and the field-to-field join constraint on a computer readable storage medium.
1. A computer-implemented method of creating a database abstraction model, comprising, by operation of a least one processor: defining a database abstraction model, wherein the database abstraction model defines a plurality of logical fields for composing abstract queries via an interface, wherein each logical field specifies (i) a name for the logical field and (ii) at least an access method that maps the logical field to data in an underlying physical database; defining, for the database abstraction model, a field-to-field join constraint based on an identified logical relationship for a group of logical fields, wherein the field-to-field join constraint defines how a set of query results retrieved for the group of logical fields should be joined together for purposes of being output; wherein an abstract query composed via the interface and including the group of logical fields is a format suitable to be transformed by a runtime component into a resolved query of the database; and storing the database abstraction model and the field-to-field join constraint on a computer readable storage medium. 2. The method of claim 1 , 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 into which instance of a set 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.