relation-clause        A clause that specifies a context
                           variable for a stream or a loop. For
                           more information see the entry on Context
                           Variables.

    field-name             The name of a field in a relation. For
                           example, once you have defined E as
                           the context variable for the EMPLOYEES
                           relation, E.LAST_NAME is a value
                           expression that refers to a value from
                           the LAST_NAME field of EMPLOYEES.