To design and write a client program to run an existing CICS® 3270 transaction using the Link3270 bridge you need to:
The following scenarios describe some common client environments. They show how you can develop your client program to run in the most appropriate environment to make best use of existing skills and experience. These scenarios demonstrate tiered client applications that enable you to divide the logic to make best use of skills and experience. They use some common terms:
In this scenario, shown in Figure 7, the programmer has CICS skills and experience, so it is more appropriate to write the Link3270 interface code on CICS.
You can separate the client logic into a business client, and a bridge client.
The LINK and EXCI samples show how a client application can be separated in this way and how common logic can be shared in the bridge client. Note that a business client in another CICS region can use DPL to access the bridge client.
In this scenario, shown in Figure 8, where a CICS product is installed on the workstation ( such as CICS for Unix) then the client can be a CICS program using LINK to interface with Link3270, or with a host CICS bridge client. In the three tier model the writer of the bridge client needs to have CICS skills, but the business client programmer only needs skills on that platform.
In this scenario, shown in Figure 9, the programmer has workstation skills and limited CICS experience. For the two tier scenario, the programmer must have some CICS experience to understand the messages (which involve EXEC CICS instructions).
The client program executes on a remote workstation, using ECI to drive the user application. A single client program is written, combining the business logic in the client environment and the interface to Link3270.
In this scenario, shown in Figure 10, the workstation business client calls a bridge client in another environment, perhaps to utilize existing skills. For example, a Unix program could send a user-defined XML message to Websphere on OS/390®. A user-written bridge client application in Websphere could then parse the XML message and convert it to a Link3270 message and use an EXCI LINK to call Link3270.
You need to analyze the 3270 application programs that form your transaction in order to replace the 3270 input data with messages sent by your client program. You can use the 3270 Bridge Passthrough SupportPak ( See Using the 3270 Bridge Passthrough SupportPak) to drive your applications and log 3270 commands.
3270 programs fall mainly into the following types:
Link3270 has two modes of operation:
Your client program manages the sequence of requests and the creation and deletion of the bridge facility. Note that this is different from the implementation of the START bridge, where the bridge facility is created dynamically.