Lets you declare a context variable for a stream or a loop.
    Once you have associated a context variable with a relation,
    you can use only that context variable to refer to records from
    that relation in the record stream you created. Each relation
    (including multiple uses of the same relation) in the record
    stream must have a unique context variable. For more information
    see the entry on Context Variables.

1  –  Examples

    The following programs demonstrate the use of the relation clause
    with a FOR loop. These programs declare a context variable E for
    EMPLOYEES. This allows the programs to reference records from the
    EMPLOYEES relation by using the variable E in the host language
    print statements.

1.1  –  C Example

    #include <stdio.h>
    DATABASE PERS = FILENAME "PERSONNEL";

    main()
    {
    READY PERS;
    START_TRANSACTION READ_ONLY;

    FOR E IN EMPLOYEES
       printf ("%s  %s  %s\n", E.LAST_NAME,
                               E.EMPLOYEE_ID,
                               E.SEX);
    END_FOR;

    COMMIT;
    FINISH;
    }

1.2  –  Pascal Example

    program context_variable (input,output);
    DATABASE PERS = FILENAME 'PERSONNEL';

    begin
    READY PERS;
    START_TRANSACTION READ_ONLY;

    FOR E IN EMPLOYEES
       writeln (E.LAST_NAME, ' ', E.EMPLOYEE_ID, ' ', E.SEX);
    END_FOR;

    COMMIT;
    FINISH;
    end.

2  –  Format

  (B)0relation-clause =

  qq> context-var qqq> IN qqwqq>qqqqqqqqqqqqqqqqqqwqq> relation-name qq>
                            mqq> db-handle qq> . qj

2.1  –  Format arguments

    context-var            A context variable. A temporary name that
                           you associate with a relation. You define
                           a context variable in a relation clause.
                           For more information see the entry on
                           Context Variables.

    db-handle              Database handle. A host variable used
                           to refer to a specific database you have
                           invoked. For more information see the
                           entry on the Database Handle clause.

    relation-name          The name of a relation in the database.