Currently we secretly supports referenced nested workflow. Such a nested workflow is saved in the scufl as:
However, as pointed out by Paul Fisher to taverna-users on 2007-07-30, this means that if G: was your USB flash-drive at home, it might be at F: at work. If you are using it in a Linux or Mac OS X computer it would work even less.
In general our GUI doesn't show that a nested workflow is referenced, and doesn't give the user any control over when it is referenced or not.
Referenced workflows are generally very useful, as reported (offline) by Marco Roos, for utillity workflows/shims that can be built and maintained separately. Within their personal library of workflows they would generally like to use the latest version of that nested workflow, ie. the one stored behind the reference.
Currently if you start editing a nested workflow Taverna will make a copy of it and break the reference. This might or might not be what the user wants.
This Improvement request seeks a general clean-up of how Taverna handles referenced nested workflows and to improve the GUI to make referenced nested workflows more obvious and usable.
Most of Taverna's users probably don't even know that referenced nested workflows are possible, and keeping it secret is like not telling a fresh programmer about functions.