On Fri, Jan 28, 2011 at 13:36, Guzmán Llambías - INCO
<[email protected]> wrote:
> I'm very interested in using the Failover Handler of the Taverna dispatch
> stack described in Taverna, reloaded paper, but I couldn't found any further
> docs or see how to configure it in the workbench. Could you please point me
> a link to some docs I could use?


The Taverna 2 workflow engine supports this, but we've unfortunately
not yet added a way to add the alternative services in the Taverna 2
user interface.


Taverna 1 supports this, if you build such a workflow in Taverna 1 and
open it in Taverna 2, Taverna should keep both services and make use
of the Failover mechanism. In Taverna 1 you need to add 'alternative
processors' [2] and then do the port mapping.


Note that in some cases your alternative might not match exactly on
inputs or outputs, the best case then is to use the Abstract Processor
and add both real services as alternatives - you can create enough
ports in the Abstract processor to cover all ports. In the case of a
service missing an output port you should wrap the alternates in
nested workflows to provide default values on the missing ports.

In the case that the alternative needs a more complicated call pattern
(like a create-run-get-result) you can add the nested workflow as an
alternate - but note that in Taverna 2 errors in a nested workflow
will not trigger the Failover.

 (In the architecture paper you might see that this is because the
errors would be returned as normal results from the parent Invoke
layer)


[1] 
http://www.mygrid.org.uk/usermanual1.7/workbench_windows.html#ame_alternate_processors

-- 
Stian Soiland-Reyes, myGrid team
School of Computer Science
The University of Manchester

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