What Is a Transition?

Transition Types

AquaLogic BPM provides many types of transitions. The most common transitions are unconditional, conditional, and due. The exception transition is a little bit more advanced, but is also used frequently, while the business rule transition is new:

	Transition	Description
	Unconditional	Instances flow through the transition unconditionally.
	Business Rule	Instances flow through the transition if the specified dynamic business rule evaluates to true.
	Conditional	Instances flow through the transition if certain conditions are met.
	Due	Instances flow through the transition according to time conditions.
	Exception	Instances flow through the transition if an exception occurs.

The compensate, message-based, and precedence transitions are used less frequently. If you are just beginning to use ALBPM, you do not need to be familiar with these yet:

	Transition	Description
	Compensate	Instances flow through the transition if compensation processing is required. The actions performed reverse (or undo) any work done in the previous activity in the event that BP-method failure occurs.
	Message-based	Instances flow through the transition if the activity that manages different argument mappings receives a message.
	Precedence	Only available in a Split-Join circuit. Copies within a Split-Join circuit can have a synchronization or a precedence. The precedence is represented by a dotted transition.

Which transition is used?

All activities at least have an outgoing unconditional transition so there is always a way to continue the process. However, in most real-world processes several activities also have outgoing conditional transitions. In this case, the conditional transitions are evaluated first, and the unconditional transition is taken only if the conditional transitions all evaluate to false. In programming terms, the unconditional transition is like an else clause in an if-then-else construct.

Business rule transitions are evaluated before conditional transitions, so if a business rule transition and a conditional transition both evaluate to true, the business transition is used.

Due transitions act separately. They "pull" the instance from the activity as soon as a time condition is met. In this case, all other outgoing transitions are ignored.