You can see if there's iteration going on by looking at Details and
Predicted behaviour. When the depth numbers don't match the service, the
Implicit Iteration is in action.
http://dev.mygrid.org.uk/wiki/display/taverna/Implicit+iteration
List handling is detailed here:
http://dev.mygrid.org.uk/wiki/display/taverna/List+handling - which affect
the depth of the outcoming lists. The use of nested workflow for tweaking
list handling is towards the end of the page.
On 20 November 2013 09:15, Pinar Alper <[email protected]> wrote:
> Hi Donal,
>
> there were several cases in the data where I could not make sense of the
> decision to use sub-workflows. Those can be attributed to list handling,
> then.
>
> I do not 100% understand the example below. I need to experiment myself
> with it using the workbench.
>
> thanks for the response.
> pinar
>
>
> > On 18/11/2013 14:48, Stian Soiland-Reyes wrote:
> >> For instance, if there are iterations over the nested workflow, now
> >> you would have iterations over the immediate first processors instead
> >> (and their downstreams) - which might in some cases require you to
> >> reconfigure List Handling on every step of the workflow.
> >>
> >> Many nested workflows are used with iterations both inside and outside
> >> the nested workflows - in which case there are several List Handling
> >> iteration patterns which can't easily be expressed on a merged
> >> workflow, say outer Dot product and inner Cross product.
> >
> > Another cast that I hit recently relates to the ways in which merges
> > work; if you want to form (apologies for pseudo-SML syntax):
> >
> > 'a list • 'b list • 'c list -> ('a • 'b • 'c) list
> >
> > without using a beanshell, you end up using a merge inside a nested
> > workflow, where the depth of the inputs to the nested workflow are 0 but
> > the values being fed in are lists. Remove the nesting and you get a
> > *completely* different operation which has an outer list which has the
> > three input lists as sub-lists; the outer list is working like a
> > poor-mans tuple. (FWIW, in my particular case, the three values are
> > actually derived from a single input by applications of — decidedly
> > non-trivial — functions, so I can guarantee that doing a dot product
> > works.) Changing the workflow to deal with the fact that the merges now
> > fail would involve introducing an entirely new processor. (I also
> > suspect that we perhaps ought to flag up any workflow that has a merge
> > of a value of depth greater than 0 as being potentially problematic; the
> > “poor-mans tuple†is a categorical canary in the type mine.)
> >
> > I also use nested workflows for looping control and the workflow
> > concerned would *not* work without it. But Stian's already mentioned
> that.
> >
> > The long and short of it is this: nested workflows are a critical
> > feature of Taverna. You can't unnest in all but the most trivial of
> > cases; if you want to understand anything complicated, you'll have to
> > deal with directly nesting. :-)
> >
> > Donal.
> >
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>
>
> --
> regards
> pinar
>
>
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--
Stian Soiland-Reyes, myGrid team
School of Computer Science
The University of Manchester
http://soiland-reyes.com/stian/work/ http://orcid.org/0000-0001-9842-9718
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