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Note
titleErrors are also completions

Note that a service is said to have _completed_ even if it returned an error in one or more of its iterations.

Taverna 2 requires all parts of the workflow to return a value, even if it is an error document. Downstream services receiving an error should normally return a new, derived error directly - but error documents are not delivered to control links.

This is different from Taverna 1 behaviour, where control links were only activated if the full iteration was completed. In some Taverna 1 workflows control links were used together with local workers like Fail_if_true to build a crude form of branching mechanism. Some Taverna 1 workflows using this technique would not run as expected in Taverna 2. However, most cases have been found to simply be invoking asynchronous services, which in Taverna 2 can be used better by enabling looping.

There are plans to develop native branching for Taverna 2.

Panel
  1. From Control links in the Workflow Explorer, right-click the control link to delete and select Delete control link.

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