# Message Flow

Substation ES accepts Rendezvous or Enterprise Message Service messages that originate from applications anywhere on the network. Conversely, Substation ES also accepts messages or events generated by transactions that are running within the CICS or IMS regions on z/OS.

Within the scope of Substation ES, messages and requests are synonymous. Substation ES transforms the following types of messages, enabling them to be passed between applications.

- Requests from TIBCO BusinessWorks or other TIBCO messaging applications to obtain data from a transaction processing application such as CICS or IMS. In those cases, Substation ES returns a data set to the requesting application.
- Requests from TIBCO BusinessWorks or another TIBCO messaging application for data to be supplied to a transaction processing application such as CICS or IMS. No return data sets apply, but there might be a status return, that is, an acknowledgment of receipt.
- Requests (trigger events) from a transaction processing application such as CICS or IMS to supply data or events to listening TIBCO messaging applications.

There are two types of message flow:

- Requests or Replies

  Substation ES can subscribe to messages generated by external TIBCO applications, transform the messages into a z/OS data format, and pass them to CICS or IMS systems for processing. For example, a TIBCO application can publish a request for data to a CICS or IMS application that runs on z/OS. Optionally, that application responds with an acknowledgment or returns a result set.

- Triggers

  Substation ES can also publish data on behalf of CICS or IMS applications, that is, translate the data from the z/OS format and package it as an ESB message for delivery to an external application that subscribes to the data.

  When Substation ES receives a request, it does the following:

  1. Checks the authentication file of the request for authenticity and verifies if the format is valid.
  2. Sends the request to ESB Interface for data translation.

ESB Interface translates data types and formats between TIBCO applications and CICS or IMS applications according to the translation definitions specified in the transformation configuration panels. The data mapping defines how each field in a given message is translated as it is passed from a TIBCO application to the CICS or IMS application and vice versa.

Substation ES interfaces serve as the mechanism for communicating and passing information between Substation ES and transaction processing systems, databases, and other services that are available on z/OS. Substation ES interfaces give TIBCO applications on any platform a means of accessing platform-specific applications on z/OS. Substation ES interfaces for z/OS are robust, scalable, and capable of delivering a high level of transaction throughput.

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