A question regarding Index Sizes (Curiosity mainly!!).

For some time now, I have been intrigued about the "index size" which is reported by the supplied utilities such as dbschema and dbexport. For example: { TABLE "dba".table1 row size = 81 number of columns = 3 index size = 12 } ^^^^^^^^^^^^^^^ create table "informix".notes ( integer1 integer, smallint1 smallint, char1 char(75) ); revoke all on "dba".notes from "public"; create index "dba".table1_idx on "dba".notes (integer1); From my understanding in the manuals, the to calculate the size of the index, it is the (length of the fields in the index) + 4, so theoretically I was expecting to see 8 as the index size (integer length 4 + 4). After some fiddling, trying out different indexes etc. and seeing what dbschema was reporting in each case, a formula has come to light of how the utilities calculate their reported amounts. This formula is as follows, where k = sum(length of each field in index): index size = k + int(k/2) + 6 This works with every table in our schema. Just out of curiosity, I was wondering if anyone can enlighten me as to why this formula is used by the utilities, since I cannot relate it back to the manuals in any way at all ? --StuK.