I have Events that are coming in from an external source. My thought was that I would import them into my Kentico site's SQL Server once a day so they can be displayed in Kentico along with events that are created in Kentico. There are a bunch of additional fields they want to capture from the basic Event document type and some of them are lookup values to other SQL tables. The problem is that they need to support multi-select values for some fields. For example, category might have multiple values.

Is there away to setup a multi-select value for a field in a document type? I can see there is a way to show drop down lists and radio buttons but I need the ability to select mutliple values. If I cannot do it in a document type, can I do it in a system table?