If you want to make a request, in the middle of your flow, to an external system, and put the result into the message tree, use a request node.
This node provides a flexible interface with a wide range of functions. It also has properties that you can use to control the way in which the interaction participates in transactions.
You can control the way in which the database is accessed by this node by specifying user and password information for the data source that you specify in the node properties. Use the mqsisetdbparms command to initialize and maintain these values.
You can update only databases from this node; you cannot update message content. If you want to update message content, use the Compute or Mapping node.