For IMS applications using the 2PC protocol, IMS acts as a coordinator and manages the 2PC processing.
A database becomes a resource that can be controlled by IMS system events, such as syncpoint and rollback.
For more information on the coordinator and 2PC in general, see the section on 2PC in Teradata Vantage™ - Database Administration, B035-1093 or Teradata® Call-Level Interface Version 2 Reference for Mainframe-Attached Systems, B035-2417.
For more information on 2PC and IMS, see DB2 Administration and IBM IMS Communication and Concepts.