The Professional User is normally a Business Analyst or IT person.
They can organize the data fields company wide for the Viewer Users. They may or may not know the relational database model but probably know the business data model quite well.
They may be a power user and know how to write some SQL Queries, although it's not a requirement.
Sometimes considered the Gatekeeper of the data. They determine which data fields viewers can access and how that data will be initially organized into Business cases.
Professional Users are the first line of support for the Viewer Users. It's required that this user receive training from Data Selections on how to use the system.
If there are no Enterprise Users then this user is the Administrator of the system. Heavily involved during any implementation process or data discovery.
Professional Users can create User Defined Formulas but should be well versed in the SQL Query Language to do so effectively.