Designing a message flow

When you design a message flow, consider the following questions and options:

• The mode that your integration node is working in can affect the types of message flow node that you can use and the number of message flows you can deploy. For more information, see Restrictions that apply in each operation mode.
• Which message flow nodes provide the function that you require. In many cases, you can choose between several nodes that provide a suitable function. You might have to consider other factors listed here to determine which message flow node is best for your overall needs. You can include built-in nodes, user-defined nodes, and subflow nodes. For more information, see Deciding which nodes to use.
• Whether it is appropriate to include more than one input node. For more information, see Using more than one input node.
• How to specify the characteristics of the input message. For more information, see Defining input message characteristics.
• Whether to determine the path that a message follows through the message flow, based on the content or the characteristics of the message. Several message flow nodes provide checks or examination of the message, and have output terminals that can be connected to direct certain messages to different message flow nodes. For more information, see Using nodes for decision making.
• Whether it is appropriate to split message flow processing between different locations. A message flow can call another flow directly. You can deploy both flows to IBM Integration Bus or IBM App Connect on IBM Cloud. You can also deploy one flow to IBM Integration Bus and one flow to IBM App Connect on IBM Cloud. Callable flows also facilitate reuse because they can be called by multiple message flows. For more information, see Splitting the processing of message flows.
• Whether you can use subflows that provide a well-defined subset of processing. You might be able to reuse subflows that were created for another project (for example, an error processing routine), or you might create a subflow in your current project, and reuse it in several places in the same message flow. For more information, see Subflows.
• What response times your applications expect from the message flow. This factor is influenced by several aspects of how you configure your nodes and the message flow. For more information, see Optimizing message flow response times.
• Whether your message flow processing makes demands on system resources such as stack size. For more information, see System resources for message flow development.
• Whether you can use the destination list in the local environment that is associated with the message to determine the processing in the message flow (for example, by using RouteToLabel and Label nodes), or the target for the output messages (for example, by setting the Destination Mode property of the MQOutput node to Destination List). For more information, see Creating destination lists.
• Whether to use WebSphere® MQ cluster queues. For more information, see Using WebSphere MQ cluster queues for input and output.
• Whether to use WebSphere MQ shared queues on z/OS® . For more information, see Using WebSphere MQ shared queues for input and output (z/OS).
• Whether to validate input messages that are received by the input node, or output messages that are generated by the Compute node, or both. For more information, see Validating messages.
• Whether to view or record message structure in Trace node output. For more information, see Viewing the logical message tree in trace output.
• Whether your message flows access data in databases. You must configure integration nodes, databases, and database connections to enable this function, as described in Working with databases. You must also configure your message flows; see Accessing databases from message flows.

  If you include message flow nodes that use ESQL, for information about how to code the appropriate statements, see Accessing databases from ESQL. If you want to access databases from Java™ nodes by using JDBC, see Interacting with databases by using the JavaCompute node or Extending the capability of a Java message processing or output node.

• Whether your message flows access data in files. By using the FileInput and FileOutput nodes, your message flows can read messages from files and write messages to files in the local file system, or on a network file system that appears local to the integration node. For more information, see Connecting client applications.
• Whether your messages must be handled in a transaction. You can set the properties of some built-in message flow nodes to control how transactions are managed, and how messages are processed in a transaction. For more information, see Configuring transactionality for message flows.

  If you want to include JMSInput and JMSOutput nodes in your message flow transactions, you must consider the additional information in Configuring JMS and SOAP nodes to support globally coordinated transactions.

• Whether you want your messages to go through data conversion. For information about the available options, see Configuring message flows for data conversion.
• Whether you want to use the MQGet node. For more information about how messages are processed by the MQGet node, and a description of request-reply scenarios that uses this node, see Working with WebSphere MQ.
• How your message flows can benefit from user exits. For more information, see Exploiting user exits.
• What steps to take to ensure that messages are not lost. For more information, see Ensuring that messages are not lost.
• How errors are handled in the message flow. You can use the facilities provided by the integration node to handle any errors that arise during message flow execution (for example, if the input node fails to retrieve an input message, or if writing to a database results in an error). However, you might prefer to design your message flow to handle errors in a specific way. For more information, see Handling errors in message flows.
• Whether you want a systems monitoring tool to be able to query, discover, and set certain user-defined properties at run time. For more information, see Setting message flow user-defined properties at run time by using a custom integration application.