HP NonStop G-Series - Manual (Page 21)

Client Programming
Introduction to the Tandem DDE Gateway
110838 Tandem Computers Incorporated 1–9
PROCEDURE DIVISION.
BEGIN-TRANSACTION.
(not really needed for this read-only transaction)
SEND READ-REQUEST-MESSAGE TO EMPLOYEE-SERVER
REPLY CODE 1 999 YIELDS READ-REPLY-MESSAGE.
IF REPLY-CODE = 1
END-TRANSACTION
ELSE
ABORT-TRANSACTION.
The SCOBOL SEND verb sends a message containing one binary number
(EMPLOYEE-NUMBER) to a Pathway server called EMPLOYEE-SERVER. The
Pathway server replies with READ-REPLY-MESSAGE, which contains four data items
of various data representations. The first data item in READ-REPLY-MESSAGE
indicates the success or failure of the request.
Tandem DDE Gateway
Communication
Approaches
You can implement a transaction using the Tandem DDE Gateway in either of two
ways: element-by-element or binary-pass-through. You can also use both the element-
by-element and binary-pass-through approaches within one application, one client
program, or even within one DDE conversation. The element-by-element approach is
easier to program and maintain than binary-pass-through and can be used from client
applications and tools that have limited or no capability for defining message layouts.
You can prototype a client application using the simpler element-by-element approach
and, after reviewing the performance of the prototype, change the parts of the
application needing the highest performance on the workstation to use binary-pass-
through.
See Section 4, “Creating Client Applications,” for more information on how to use both
communication approaches. Also, examples of both approaches used in a variety of
client tools and applications are supplied in the EXAMPLES subdirectory of the
Tandem DDE Gateway on the workstation.
Note Tandem system and data communications network resource usage is the same for both element-by-
element and binary-pass-through approaches.
See Section 7, “Using DDE Hot and Warm Data Links,” for more information on how
to use RSC Unsolicited Message Service (UMS) with DDE hot and warm data links.
Element-by-Element
Approach
The element-by-element approach requires that you first define the message layouts in
Tandem’s Data Definition Language (DDL), then use the Tandem DDE Gateway
Bridge program on the host to construct a DDE Gateway Dictionary. The DDE
Gateway Dictionary is then downloaded to the workstation so that data conversion
can be done automatically by the Tandem DDE Gateway.
This approach uses more workstation processing because data elements that make up
the messages are communicated one at a time between the client application and the
Tandem DDE Gateway. The Tandem DDE Gateway converts the data elements to and
from its buffers with the assistance of the workstation-based data dictionary created by