I have a screen where user can select multiple values from the database. This screen follows a standard used in every screen with similar cadastre, where de data being edited or created is shown on the top, a table with the existing data is bellow and some action buttons at the bottom. So, following this standard, I've created the following screen:
In the field "Operações", the user can select multiple options, according with the tuples in the database.
As you can see, this control has usability issues. The user can't understand the field "Operações" is a multiple selection, simply looking at it. When he finally discovers it can select multiple values and save the registry, the data of the multiple selection isn't showed in a comprehensive way in the table:
Should I break the standard here? Should I use multiple checkboxes directly in the screen? What could I do to improve the usability of this screen?