HP NonStop G-Series - Manual (Page 25)

Client Programming
Introduction to the Tandem DDE Gateway
110838 Tandem Computers Incorporated 1–13
3. Use the DDE Execute function to tell the Tandem DDE Gateway to start a Tandem
Transaction Monitoring Facility (TMF) transaction. Use the command
[BEGINTRANSACTION]. (This step is not really needed for this read-only
transaction; it is used only to illustrate the procedure.)
4. Use the DDE Poke function to pass the data in the READ-REQUEST-MESSAGE
structure to the Tandem DDE Gateway. Binary-pass-through is being used, so the
DDE item name is _TDMGW-BINARY-BUFFER. You can use the standard
clipboard format CF_TEXT or the registered clipboard format
TdmgwBinaryBuffer. (CF_TEXT is permitted for client programming convenience
even though the message might contain embedded bytes of binary zeros.)
5. Use the DDE Execute to tell the Tandem DDE Gateway to send the request
message to the Tandem server and store the reply message in a buffer in the
Tandem DDE Gateway. Use the command [SEND].
6. Use the DDE Request function to tell the Tandem DDE Gateway to return the
reply message to the READ-REPLY-MESSAGE structure in the client application.
Use the DDE item name _TDMGW-BINARY-BUFFER. You can use the clipboard
format CF_TEXT or the registered clipboard format TdmgwBinaryBuffer.
7. Use client code to convert the data in the READ-REPLY-MESSAGE structure from
the Tandem formats returned by the server to the formats most convenient for
processing by the selected client tool.
8. Use the DDE Execute function and either the [ENDTRANSACTION] or
[ABORTTRANSACTION] command to either end or abort the TMF transaction.
Another DDE Execute function with the [INITIALIZESERVICE...] command could
be used here to start another type of transaction, for example, to update employee
data. Or the same transaction type can be done again without another
[INITIALIZESERVICE] command.
9. Use the DDE Terminate function to finish the DDE conversation with the Tandem
DDE Gateway.
Client Programming
Considerations
Generally, you should keep DDE conversations as short as possible—to initiate and
terminate a DDE conversation uses few workstation resources and causes no data
communications traffic. When you start a DDE conversation and issue the first DDE
Execute INITIALIZESERVICE command, data communications resources are
temporarily allocated by the Tandem DDE Gateway to the client application and are
temporarily denied to other client applications on the workstation.
If you plan to use the binary-pass-through approach to communicate with the Tandem
DDE Gateway, the client tool must be able to define message layouts exactly as
required by your Tandem servers. Review the data types used in your Tandem server
messages and consider how they could be represented in the client tool’s language and
converted between client tool and Tandem data representations. Also, decide how
special structures such as tables, data redefinitions, and application-specific data types
in Tandem server messages (such as timestamps) could be implemented.