various improvements

[EvanBldy]

Problem

• There's no index and primary key for department link table.
• There's a typo.
• Some requirements are outdated.
• When editing a metadata-descriptor we don't always check data_type.

Solution

• Add an index and a primary key for department link table.
• Fix typo.
• Upgrade outdated requirements.
• Always check data type to avoid errors when editing a metadata descriptor.