Presented foreseen changes to Invenio workflows and external workflow module (see also WIP branches in the attached links).
In summary, we are simplifying and clarifying the interface to add your own workflow engine implementations. We are adding an example persistent implementation that invenio further expands.
We propose to remove some legacy support for TokenizedDocument/Pheonix/Seman to simplify code. RFC's will be posted. RFC located here.
On the Invenio side, we have adopted to use the new way of extending a workflow engine, alongside improvements to accessing the `data` attribute (removing the need for `get_data`) and other simplifications.
Several parts of the Invenio workflows module have been fully or partially ported towards the external workflow module, such as the mid level API `client.py`.
Furthermore, we propose to remove support for the BibWorkflowEngine model as we do not see the need to store these instances in a persistent way. BibWorkflowObject (the data wrapper) should be sufficient.
Tibor brought up the current issue of inconsistency between persistent object states and the workflow definition should the definition suddenly change order of tasks. This is still not addressed, but adding so-called "labels" to task functions could be one direction.
The Holding Pen web interface that is used to display and manage data objects in workflows still remain in the Invenio workflows module.
Regarding TaskFlow, we have looked briefly into it and it has some interesting features (such as built-in undo support and other ways of traversing a workflow). It could be nice to look at it further, and perhaps use it in some other context, but speaking from the INSPIRE perspective for the short-term it is very unlikely we will put resources towards porting our workflows to it, but it can be something to pursue in the future.