Access path / index rebuilds

Hopefully someone can answer this for me in easy terms.

Why would a system rebuild access paths for files when being used by
many ODBC (QZDASOINIT) jobs?  For example, the jobs will sometimes go in
to an IDX-xxxxxxx where xxxxxxx = the name of a file.  The online help
shows that the IDX status means it's rebuilding the index (access path)
to whichever file it's listing.

What prompts the rebuild?  Is there somewhere we could go look to see
why it's doing that?  Additionally, in Performance Navigator there's a
chart for Index Rebuilds/second - the online help for describing why is
pretty vague there also.

Please advise - thanks in advance for your help and for not biting my
head off if this is basic and I just never learned it - hah!

--
Justin C. Haase - iSeries System Engineer
IBM Certified Systems Expert - eServer i5
Kingland Systems Corporation


CONFIDENTIALITY NOTICE:  This e-mail communication, including attachments, is 
covered by the Electronic Communications Privacy Act, 18 U.S.C. 2510-2521, is 
confidential, and may be legally privileged.  If you are not the intended 
recipient or believe you received this communication in error, please reply to 
the sender indicating that fact and delete the copy you received.  In addition, 
retention, dissemination, distribution, copying, or otherwise use of the 
information contained in this communication is strictly prohibited.  Thank you.