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HP NonStop G-Series User Manual

Page 16

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Features

Introduction to the Tandem DDE Gateway

1–4

110838 Tandem Computers Incorporated

Figure 1-2. Automatic Message Layout and Data Conversion

Windows

Workstation

Tandem

System

Client

Application

Tandem DDE

Gateway

Dictionary

Tandem DDE

Gateway

Dictionary

Tandem DDE

Gateway Bridge

Program

DDL Dictionary

(Message Layouts)

Download

002

Tandem DDE

Gateway

You enter the message layouts for the Tandem servers that will be used by your client
application into a Tandem Data Definition Language (DDL) dictionary. (If your
message layouts are already in a DDL dictionary, then you can use that dictionary.)
Most data types are supported for both COBOL and C servers.

You execute the Tandem DDE Gateway Bridge program on the Tandem system and
then download the resulting Tandem DDE Gateway Dictionary to the Windows
workstation. (The download is done using a Tandem product such as IXF or the
Multilan file server.) The Tandem DDE Gateway Dictionary is then used by the
Tandem DDE Gateway to define the message layouts and convert the message data.
The client application does not need to be concerned with either the layout of a
message or data conversion.

The Tandem DDE Gateway Browser tool on the Windows workstation can assist you
with client application development. You can use it to review the message layouts
defined in the Tandem DDE Gateway Dictionary and to generate skeleton code for
parts of your client application.

The second (and more difficult) option is to specify the layouts of the messages that
are exchanged with the Tandem system in the client application and also convert the
data as necessary using client application code. Some data conversion functions you
can call from your client application are provided with the Tandem DDE Gateway. It
should be noted however that some tools have limited or no capability for defining
message layouts, and even those with relatively good support, such as Microsoft
Visual Basic, have important restrictions. This option offers the possibility of the
highest performance for the client application but can cause difficulties in
development, especially when using existing Tandem servers with complex message
layouts.