Geodatabases stored on database servers (instances of Microsoft SQL Server Express) have two types of administrative users: server administrators and geodatabase administrators.
The server administrator
The server administrator is a database administrator and a geodatabase administrator rolled into one. This user can add other users to the database server, control user permissions, create and delete geodatabases, detach and attach databases, and back up and restore databases. In addition, this user can perform geodatabase maintenance tasks, such as compressing a versioned geodatabase.
Server administrators are part of the sysadmin fixed server role in the SQL Server Express instance. All members of this role are considered dbo users. In the geodatabase, that means all data owned by server administrators are owned by dbo and stored in a schema named dbo. Because the server administrator creates the geodatabases on the database server, this user owns the database and the geodatabase system objects in the database.
The geodatabase administrator
The other type of administrative user—a geodatabase administrator—is a Windows-authenticated user assigned to the SQL Server db_owner database role. This user can perform administrative tasks, such as administering other users' geodatabase permissions, making a backup of the geodatabase, and compressing the geodatabase. Geodatabase administrators cannot administer the database server or other geodatabases for which they have not been given administrator privileges.