Transitions

Basic transitions

Some processes operate in a 'straight-through' flow, where after one action is complete it flows directly to another. This is a simple connection that has no logical test and simply passes control.

For example, whatever the results entered at Action 2 in a workflow, after the action is completed, the workflow engine will trigger Action 3 to be performed.

Branched transitions

Other workflows might implement branching logic or loops which are based on these conditions:

• Parameters collected at an action level and which can be passed to phases and operation levels
• The results of a previous action carried out in the phase if, for example, a question is asked and branching occurs based on the answer

When a workflow implements branches, each branch must be considered exclusive and all branches conditions must represent 100% of the cases so that only one action can be the consequence of any given action.

For example, the logic between Actions 1 and 2 cannot match the logic between Actions 1 and 3.

If Action 1 checked the temperature, with the transition between Actions 1 and 2 being temperature ≥ 20 and between 1 and 3 being temperature < 20. Regardless of the temperature value, only one action would be triggered.

Action 3 would trigger a loop until the temperature value was 20 or more, at which point Action 2 would be triggered.

Using branched transitions, you can implement these possibilities:

• Loops in a phase, where a test is put in place to identify whether a series of actions should be carried out a second or third time in order to complete a phase
• Conditions placed on actions
• Continuous evaluation transitions

Continuous evaluation transitions

Continuous evaluation transitions are expected to evaluate to true within a given timeframe and that are continuously reevaluated periodically until the truth condition is reached. This can, for example, be used to wait on an OPC signal indicating that a process temperature has been reached.

Split transitions

In some cases it might be possible to carry out multiple actions, in any order, in parallel as the result of an action. Typically, this would be where the resources involved in each action are different so that they can be carried out independently. In workflow diagrams, a split is shown by a single inbound action with multiple outbounds.

Merged transitions

Once actions have been split into parallel running paths, all actions on all active paths must come together and be completed before a phase can be complete. Bringing together multiple split paths is called a merge. It may be the case that a phase performs multiple splits and merges, but it is very important that all paths are brought together in merge joins before a phase can be ended. In workflow diagrams, a merge is shown by a transition, with multiple inbound actions but a single outbound.

Operations transitions

Operation transitions encode the logical links between operations in a workflow.