Creates a view definition.  A view is a relation that is not
 physically stored.  Rather, it is a virtual structure that points to
 records from other relations.  You define a view by specifying:

  o  A record selection expression to name the criteria for selecting
     the relations and records
  o  A set of fields from those relations

 Example:

      DEFINE VIEW EMP_NAME OF E IN EMPLOYEES.
         E.FIRST_NAME.
         E.MIDDLE_INITIAL.
         E.LAST_NAME.
      END EMP_NAME VIEW.

Additional information available:

MoreFormatExamples

 You need the Rdb/VMS READ and DEFINE privileges to the referenced
 relations to use the DEFINE VIEW statement.

 When the DEFINE VIEW statement executes, Rdb/VMS adds the view
 definition to the physical database.  If you have invoked the
 database with the PATHNAME qualifier, the definition is also stored
 in the data dictionary.

 You must execute this statement in a read/write transaction.  If you
 issue this statement when there is no active transaction, Rdb/VMS
 starts a read/write transaction implicitly.

 Other users are allowed to be attached to the database when you issue
 the DEFINE VIEW statement.

 DEFINE VIEW ───> name ─────┐
      ┌───────────<─────────┘
      └───┬───────────────────>─────────────┬─────┐
          └──> 
D
E
S
C
R
I
P
T
I
O
N typebox (I)typebox (S) typebox (/)typebox (*) text */ ───┘     │
      ┌───────────────────<───────────────────────┘
      └──> 
O
F ───> rse ────> . ───────┐
      ┌───────────────<───────────────┘
      └─┬─┬───────────────────┬─────> name-clause ───> . ─┬─┐
        │ └──> typebox (/)typebox (*) text */ ────┘                           │ │
        └────────────────────────<────────────────────────┘ │
      ┌─────────────────────────────────────────────────────┘
      └──> 
E
N
D ────┬─────>──────┬───> typebox (V)typebox (I)typebox (E)typebox (W) ────> .
                   └──> name ───┘

Additional information available:

namersename-clause

 Name of the view definition you want to create.  When choosing a
 name, follow these rules:

  o  Use a name that is unique among all view and relation names in
     the database.

  o  Use any valid VMS name.  However, the name cannot end in a dollar
     sign ($) or underscore (_).

  o  Do not use any Rdb/VMS reserved words (See the VAX Rdb/VMS
     Reference Manual appendix for reserved words).

 A record selection expression that defines which rows of which
 relations Rdb/VMS includes in the view.  Ask for HELP on RSE for a
 complete description of record selection expressions.

 Specifies a field that you want to include in the view.

 name-clause =

 ──┬───> context-var . field-name ───────────>────────────────────┬─┐
   ├───> local-field-name ──> 
F
R
O
M ──> context-var . field-name ──┤ │
   └───> local-field-name ──> 
C
O
M
P
U
T
E
D 
B
Y ────> value-expr ───────┘ │
   ┌────────────────────────────<───────────────────────────────────┘
   └────┬─────────────────────┬────────────────>
        └┬─> dtr-clause ────┬─┘
         └───────<──────────┘

 Example 1

 You can define a view from a single relation:

 DEFINE VIEW EMP_NAME OF E IN EMPLOYEES.
    E.FIRST_NAME.
    E.MIDDLE_INITIAL.
    E.LAST_NAME.
 END EMP_NAME VIEW.

 This command file specifies a view definition derived from a single
 relation, referring to three of its fields.


 Example 2

 You can also define a view using more than one relation:

 DEFINE VIEW CURRENT_SALARY
    OF SH IN SALARY_HISTORY CROSS
       E IN EMPLOYEES OVER EMPLOYEE_ID WITH
            SH.SALARY_END MISSING.
      E.LAST_NAME.
      E.FIRST_NAME.
      E.EMPLOYEE_ID.
      SH.SALARY_START.
      SH.SALARY_AMOUNT.
 END VIEW.

 This command file defines a view from the EMPLOYEES and
 SALARY_HISTORY relations.  It uses the RSE to join the relations and
 limit the view to current salaries.  Then it lists the fields
 required from each relation.  These fields are referred to in the
 view definition as is, using the same field names as in the relation
 definition.


 Example 3

 You can give local field names to a view:

 DEFINE VIEW EMP_JOB OF E IN EMPLOYEES
   CROSS JH IN JOB_HISTORY OVER EMPLOYEE_ID
   CROSS J IN JOBS OVER JOB_CODE
   WITH JH.JOB_END MISSING.
     CURRENT_ID FROM E.EMPLOYEE_ID.
     CURRENT_NAME FROM E.LAST_NAME.
     CURRENT_JOB FROM J.JOB_TITLE.
     SUPERVISOR FROM JH.SUPERVISOR_ID.
 END EMP_JOB VIEW.

 The definition in this command file does the following:

  o  Joins the EMPLOYEES relation to JOB_HISTORY.  This join links
     employees to job history records.

  o  Joins JOB_HISTORY to JOBS.  This join lets the view contain job
     titles, instead of job codes.

  o  Uses the MISSING value expression.  This clause specifies that
     only the current job history records, where the JOB_END field is
     empty, should be included in the view.

  o  Derives the view field names from the source relations but gives
     them local names.

 The following query uses the view defined in the preceding example:

 &RDB& START_TRANSACTION READ_ONLY
 &RDB& FOR CE IN EMP_JOB
         GET
           ID = CE.CURRENT_ID;
           NAME = CE.CURRENT_NAME;
           JOB = CE.CURRENT_JOB;
           SUPER = CE.SUPERVISOR;
         END_GET
 &RDB& END_FOR
 &RDB& COMMIT


 Example 4

 The COMPUTED BY field calculates the field in the view using a field
 or fields from a component relation:

 DEFINE VIEW SS_DEDUCTION OF E IN EMPLOYEES
   CROSS SH IN SALARY_HISTORY OVER EMPLOYEE_ID
   WITH SH.SALARY_END MISSING.
     E.EMPLOYEE_ID.
     E.SOCIAL_SECURITY.
     SH.SALARY_AMOUNT.
     SS_AMOUNT COMPUTED BY (SH.SALARY_AMOUNT * 0.065).
 END SS_DEDUCTION VIEW.

 This view definition computes a new "virtual" field from the
 SALARY_AMOUNT field of SALARY_HISTORY.