Table statistics definitions

I'm trying to interpret the table level statistics (sysptprof in sysmaster) and we are having a debate about the meaning of some of the columns. Can someone please define the difference between the following: Isreads Bufreads Pagreads I believe isreads stands for ISAM-reads which refers to direct I/O from disk, bufreads would be stuff that is read from the Informix buffers, and I think pagreads refers to read-ahead pages read from disk. If this is correct, how does the reading of indexes play into isam reads? If you read an index for a table to get to a particular data value, does it count the index reads and the table reads in the isreads column for that table? I assume sequential scans are also included in isreads? Please enlighten us and help us end our debate!