All parameters for a ns operation must be structs. This is because the parameters are replicated in the Data Access Layer (DAL) and the DAL allows parameters to be structs only.
The return value for a ns operation must also be a struct. Similar to parameters for ns operations, the DAL allows return values to be structs only.
The developer must provide SQL with all ns operations; no SQL is automatically generated.
Non-standard operations must belong to an entity class. However, the SQL query can operate on any database table, it does not have to operate on only the database table belonging to the entity class; i.e., it can be used to perform SQL joins across tables.
For details on how to specify SQL in an operation, see Using Handcrafted SQL in Non-Standard Entity Operations.