A transition is the path between two activities (a 'from' activity and a 'to' activity) - it specifies that once the 'from' activity has been completed, the 'to' activity should be started. If you imagine activities as 'boxes', then transitions are the 'lines' between these boxes.

A Transition Instance records the attempt to navigate the transition between two Activity Instances (the 'from' Activity Instance and the 'to' Activity Instance).

Transitions may be conditional, i.e. once the 'from' activity has been completed, the 'to' activity should only be started if some condition (specified by the transition) is met. A Transition Instance row will be created for each transition evaluated, and for conditional transitions, the Transition Instance records whether the transition's condition was met.

Example

You define a workflow (Process Definition) to allow correspondence to be sent to customers whenever their payment details change. The activities defined in your workflow are:

• 'Start Process' (a necessary step to start the workflow which is mandated by the Process Definition Tool); and
• system prints out a letter (automatic);
• User puts the letter in an envelope and posts it (manual); and
• 'End Process' (a necessary step to end the workflow which is mandated by the Process Definition Tool).

The transitions in your workflow are a straightforward progression through the activities in the order listed above.

Person John Smith's payment details change due to an increase in rates. This increase raises an event which causes the Workflow Engine to enact your workflow and create a Process Instance.

The Workflow Engine executes the 'Start Process' activity and creates an Activity Instance. This special activity performs initialization of the workflow and completes.

The Workflow Engine identifies the outgoing transition from 'Start Process' and traverses the transition. The Workflow Engine creates a row on Transition Instance to record this traversal, linking the 'Start Process' activity to the 'system prints out a letter' activity. The system prints out the letter and completes the activity.

Similarly, upon completion of the relevant Activity Instances, the Workflow Engine:

• traverses from 'system prints out a letter' to 'user puts the letter in an envelope'; and
• traverses from 'user puts the letter in an envelope' to 'end process'.

Technical Notes

See the Workflow Guide for further information.

There is no 'Activity' database table. An activity is an XML element defined within the Process Definition metadata.

Straightforward Activity Instances will (as the workflow executes) typically have:

• a Transition Instance 'coming in', i.e. will be the 'to' Activity Instance on a Transition Instance; and
• a Transition Instance 'going out', i.e. will be the 'from' Activity Instance on a Transition Instance.

Activities which are associated with split or join points may have multiple such Transition Instances.

A Transition Instance identifies the 'from' and 'to' activities, but does not link (directly) to the Activity Instances themselves.