NET/MASTER Network Control Language (NCL) Programmer's Guide

The Structure of Mapped Data Object (MDO) Variables
Working With Mapping Services
106160 Tandem Computers Incorporated 10–11
After following the steps outlined earlier in this section to type this NCL procedure
and install it as your active MSGPROC procedure, execute the ZEX1002N NCL
procedure to send a message to your OCS window. The following screen shows the
results of executing ZEX1002N with MSGPROC active:
(06:52) --------------------- OPERATOR CONTROL SERVICES ----------------------
PROFILE MSGPROC=ZEX1004N
NNM0393 MSGPROC PROCESSING ACTIVATED
NNM0357 PROFILE HAS CHANGED
START ZEX1002N
TEST An OPER NRD message
&$MSG is
&$MSG. is . .TEST An OPER NRD
message 9 .... .. . .. ". . .. ^ ...1992/06
/15 06:52:01.090....SYS1..SYS1 ....SYS1..SYS1 ..NMTJN
..#9446690.. ....
NNM1005 START ZEX1002N PROCESSING COMPLETE. NCLID 001012
_____________________________________________________________________________
---------- ------------------ NonStop NET/MASTER D30 ---------------- --------
M=>
The screen shows that the simple variable, &MSG, has a null value and that the stem
of the MDO variable, &$MSG., refers to the data in the whole MDO variable.
This example also shows that it is generally not useful to display the contents of a
whole MDO variable, such as &$MSG.. As a general rule, it is only useful to refer to a
whole MDO variable to copy its contents to another variable. Referring to a whole
MDO variable allows you to copy large blocks of data from one variable to another.
The syntax of the ASSIGN verb that allows you to copy MDO variables is discussed
later in this section.
Elements in an MDO
Variable
An MDO variable is composed of one or more data structures called elements. An
element is the major logical data structure that Mapping Services understands. An
element consists of a header followed by a data component. The data component may
consist of other (enclosed) elements inside an outer (enclosing) element or other data
structures called groups and fields. Some enclosed elements can be repeated and are
called repeated elements.
The Header of an Element The header of an element identifies the beginning of an element in an MDO variable.
An element header consists of two parts: a length field and a key field. Figure 10-2
shows the structure of the header of an element called MSGATTR inside an MDO
variable mapped by $MSG.