HP NonStop G-Series - Manual (Page 15)

Features
Introduction to the Tandem DDE Gateway
110838 Tandem Computers Incorporated 1–3
You can drive the DDE protocol from your client application in a number of ways,
depending on the capabilities of the client tools you choose to use and the needs of
your application.
You can use the special verbs built into many client tools to drive the DDE
protocol. These are very convenient because they often include automatic error
handling and other ease-of-use features.
You can use the Microsoft DDE Management Library (DDEML) from many tools
that support Windows dynamic link library (DLL) calls. It gives you extensive
control over the use of the DDE protocol, but requires some attention to memory
management and error handling. The DDEML provides both a synchronous and
an asynchronous option for many calls. When the asynchronous option is used,
your program can continue with other processing while the Tandem DDE
Gateway is handling the DDE function.
You can use the DDE message-based C programming interface, which uses the
Windows PostMessage and SendMessage functions to drive the DDE protocol.
Programming DDE at this level requires a detailed knowledge of DDE, and you
must pay attention to error handling, memory management, and synchronization
between communicating processes. Programming at this level should rarely be
necessary when communicating with the Tandem DDE Gateway.
The Tandem DDE Gateway provides extensive configuration capabilities so that you
do not need to specify Pathway server class names, Guardian process names, Expand
node names, or data communications resources in client applications. In client
applications you refer only to transaction types (known as ServiceNames) and an
ApplicationName. In the Tandem DDE Gateway configuration files, each
ServiceName is associated with either a Pathway server class or a Guardian process
name, each ApplicationName is associated with a Pathway environment and/or an
Expand node name.
The Tandem system and IBM compatible PCs have different hardware representations
of some data types, including 2 byte integers and 4 byte integers. Data conversion is
required when these data types are passed in messages between the Tandem system
and the workstation.
Additionally, if the Tandem servers are written in COBOL (and the client application
is not), then conversions between COBOL data types and client language data types
are also necessary.
The Tandem DDE Gateway provides two options for data conversion. The first (and
easier) of the two options is to use the automatic message layout and data conversion
features built into the Tandem DDE Gateway. Figure 1-2 shows an overview of this
feature.