As per oracle help:*
DEFINE_CHAIN_EVENT_STEP Procedure: This procedure adds or replaces a chain step and associates it with an event schedule or an inline event. Once started in a running chain, this step will not complete until the specified event has occurred. Every step in a chain must be defined before the chain can be enabled and used. Defining a step gives it a name and specifies what happens during the step. If a step already exists with this name, the new step will replace the old one.
DEFINE_CHAIN_STEP Procedure: This procedure adds or replaces a chain step and associates it with a program or a nested chain. When the chain step is started, the specified program or chain is run. If a step already exists with the name supplied in the chain_name argument, the new step replaces the old one. The chain owner must have EXECUTE privileges on the program or chain associated with the step. Only one program or chain can run during a step.
Though the help documentation is elaborate, unfortunately I'm failing to understand fully. what is the difference between these two procedures?