Physical Files and Logical Files

Physical files hold the actual data of a database file. The data is written in arrival sequence.

Physical files are not required to have keyed fields. If a physical file has key fields, this is the order that an RPG program will read the data if the File Spec in the program indicates to read the data in keyed sequence.

Also, with a keyed field, an RPG program can CHAIN, SETLL, READE and READP.

A simple logical file is a different view of the physical file. It is actually a list of pointers to the physical file. Most of the time, a logical file is nothing more than a way of accessing the physical file with different key fields.

With the standard AS/400 supplied tools, it is hard to see the logical file. One way is to use the copy file CPYF to copy the logical file to a new physical file. Then, look at the physical file... it will be in the same order as the logical file.

The AS/400 Database is full featured. Logical files can join multiple files and select and create new fields.

Back to Basic AS/400 Tips    |    Back to Main Page    |   Contact Info