Questions conerning the Optimizer

I have a couple of questions: I was looking at the sqexplain table ( in sysmaster ) and was wondering, how does the cost based optimizer use these values to determine the optimization method to be used? ( I was trying to guess upon what methods were being taken, but my guesses were starting to not starting to make sense. Database is Informix ODS 7.14UC patched ) Now this question is not very important, but I would like to know if there is a way to tell 'SET EXPLAIN' to dump it's information out to a filename other than 'sqexplain.out'? In a stored procedure? Thaks, ( : - 7 ) Carlos