Use Many2One to specify actions and views Models
On action and view the model is specified using a char field which allows to introduce a model that does not exists
From https://tryton-rietveld.appspot.com/32831002/diff/40001/trytond/ir/action.py#newcode618 it will be better to use Many2One fields from action and view models, so we get the consistency check on the database.
As we have to rename the fields (due to migration) i think it's a good moment to review their name and unify them. Currently the following names are used:
ir.action.act_window -> 'res_model'
ir.action.act_window -> 'context_model'
ir.action.wizard -> 'model'
ir.action.report -> 'model'
ir.ui.view -> 'model'
I don't have a clear postion about the name of the new fields.