Answer

When creating your model, you will notice that you have the option of making each field 'required.'

Marking a field as required has implications for all collection types:

• For repository collections, any required model field will be shown with a red asterisk in the collection to model mapping.  
• For gateway collections, you will need to pass in a value in the payload for any required field in order for Hub to accept the payload.
• For database collections, the suggested DDL will mark the field as required ("not null"); this means that if you use that suggested DDL to create your database tables, the field will be required by your database table to create a new record about an artifact:

You can learn more about the 'required' model field designation here.