Locking Fields - Controlling Access by User
It's all a matter of who can do what to which records. Field access can be controlled completely with FileMaker 7's new Accounts and Privileges area. But learning how to limit what users can do is only one part to the puzzle. If you really want to know how to control what users can, and cannot do, then it's validation that you need to become familiar with.
This video article, and example file, cover the concept of locking a notes field so only the creator can determine when the field can be modified by other users of the database. If you want a better understanding of accounts and privileges and how to limit who can make changes to which fields then this video has what you need.