In a standard table individual records are uniquely identified by one or more columns of any type. The driver is informed about these columns by specifying the (unique) index made up of the columns. The index that is used to define the identifying columns is called the primary index.
Most tables have one or more column combinations that uniquely identify records. Such a combination is called a key. In most databases you can assign one of the keys to be the primary key. If a primary key exists it is the most likely candidate to be setup as primary index.
There are two programming styles that can be used to handle tables in the Application framework: RowId and RECNUM style. When using standard tables, the RECNUM style cannot be used, RowId style is mandatory.