Expert: Concise Systems/Laird Scranton - 9/8/2002

Question
I am a new IT student. Please can you briefly explain how the AS400 supports a database? I am logged on to the AS400 every day at work, but I have no idea how it works.

I need this information for a class paper.

Many thanks..........Donna

Answer
Hi Donna.

The AS/400 is very different from PC-based systems.  In what's called 'native mode' (the mode it was designed to run in), database files (physical files)are compiled from DDS source code that describes each of the fields in the record - a field name, field length, number of decimal positions (if numeric), default column headings, and even sometimes range-checking and validity-checking rules.  When a programmer writes a program that uses one of these files, the program automatically has knowledge of the fields in the file.  The AS/400 also supports what are called logical files, which are intelligent indexes over the physical files, which can automatically select certain records based on values in fields and present the data in any sequence. As data changes in the physical files, logicals can dynamically adjust to reflect the new data in the file.  For instance, if a logical file includes only invoices with a balance amount, when an invoice becomes fully-paid it automatically "drops out" of the logical view.  One key difference between PC and AS/400 databases is that PC files are typically coded using the ASCII method, while AS/400 files are coded using the EBCDIC method.

Hope this information helps!

Laird Scranton
Consultant