Patterns: Implementing Self-Service in an SOA Environment

196 Patterns: Implementing Self-Service in an SOA Environment

Two J2EE Connector CICS resource adapters are provided with the IBM CICS

Transaction Gateway (CICS TG):

򐂰 External Call Interface (ECI) is a call interface to COMMAREA-based CICS

applications.

򐂰 External Presentation Interface (EPI) is an API to invoke 3270-based

transactions.

ECI resource adapter

The CICS ECI resource adapter uses the External Call Interface (ECI) of the

CICS Transaction Gateway to communicate with CICS. It can link to CICS

programs, passing data in a buffer called a COMMAREA. The J2EE Connector

resource adapter archive (RAR) file is cicseci.rar.

EPI resource adapter

The CICS EPI resource adapter uses the External Presentation Interface (EPI) of

the CICS Transaction Gateway to communicate with CICS. It can start CICS

transactions by interacting with a

virtual terminal. The virtual terminal represents

a 3270 terminal to the CICS TG user. The J2EE Connector RAR file is

cicsepi.rar.

7.4.7 Selecting a CICS resource adapter

In this section we consider the characteristics of the two CICS resource adapters

(EPI and ECI) and the situations in which each would be selected:

򐂰 External Call Interface (ECI)

ECI uses COMMAREA as an interface to a CICS enterprise application. If the

enterprise application is not using COMMAREA as an interface, it needs to be

modified to use COMMAREA. The development effort for a session bean that

has an interface with a CICS ECI resource adapter is relatively small. This is

because ECI has a simple calling type interface rather than the

screen-oriented, conversational type interface of EPI. For this reason, we

recommend that ECI be used for new enterprise applications that will be Web

enabled. You can separate business logic in the enterprise tier from

presentation logic residing in an application server.

򐂰 External Presentation Interface (EPI)

EPI uses a 3270 data stream as an interface to a CICS 3270 application. If

the enterprise application is a 3270 CICS application, EPI should be used for

the resource adapter. There is no need to change the enterprise 3270

application at all. Using J2EE Connector Architecture CCI, the EPI application

can use the same interface as ECI, but the underlying interface is

conversational.