HP NonStop G-Series User Manual

Page 22

Client Programming

Introduction to the Tandem DDE Gateway

1–10

110838 Tandem Computers Incorporated

the Bridge program. You can configure a memory cache on the workstation for the
data dictionary to ensure good performance.

Element-by-Element DDE Communication

To explain the element-by-element approach, the client application steps necessary to
perform the transaction to retrieve employee data (described above in SCOBOL) are
shown in Figure 1-4.

Figure 1-4. Element-by-Element DDE Communication

Initiate (TDMGW , PATHWAY)

Execute ([BEGINTRANSACTION])

Poke (EMPLOYEE-NUMBER, CF_TEXT, Employee no.)

Execute ([SEND])

Request (REPLY-CODE, CF_TEXT)

Data (Value of REPLY-CODE)

Execute ([ENDTRANSACTION])

Terminate

Execute ([INITIALIZESERVICE(READ-EMPLOYEE)]

Request (LAST-NAME, CF_TEXT)

Data (Value of LAST-NAME)

Client

Application

(Element-

by-

Element)

Tandem

DDE

Gateway

(Message

Layouts

and Data

Conversion

in Tandem

DDE

Gateway)

004

Use the DDE Initiate function to start a DDE conversation with the Tandem DDE
Gateway. Use the application name TDMGW and the DDE topic name
PATHWAY.

Use the DDE Execute function to tell the Tandem DDE Gateway the transaction
type. Use the command [INITIALIZESERVICE(READ-EMPLOYEE)]. The
transaction name READ-EMPLOYEE is configured in the Tandem DDE Gateway
as a ServiceName object and cross-referenced there to a Pathway server class.

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.)

Use the DDE Poke function to pass the value of the EMPLOYEE-NUMBER data
element of the READ-REQUEST-MESSAGE to the Tandem DDE Gateway. You
refer to the EMPLOYEE-NUMBER data element in the DDE Poke function by its
fully qualified name of READ-REQUEST-MESSAGE. EMPLOYEE-NUMBER (the
fully qualified data element names are not shown above due to a lack of space).