4.2.2 Types of Fields in a File Definition
LANSA file definitions can contain 3 types of fields:
Real fields
These are the normal fields found in any file definition and are assembled together to form the record format of the associated physical file. Such fields actually exist in the database file and their content (or value) can be extracted from any record in the file at any time. (Refer to 4.2.4 Adding Real Fields to a File.)
Virtual fields
These are fields that do not actually exist in the IBM i database file, but are dynamically derived from "real" fields in the file. (Refer to 4.4 Virtual Field Development.)
Predetermined join fields
These are fields defined on access routes to receive information retrieved from the file accessed by the access routes. (Refer to 4.6 Access Route Development and 4.7 Predetermined Join Field Development.)