Thread: Problem with delete trigger: how to allow only triggers to delete a row?

I have a table where some rows are originally entered, and others are  
logically deduced from original rows by triggers.  For instance, if  
one row contains data indicating that "A < B" and another row  
indicates "B < C", the triggers will generate a new row indicating  
that "A < C".  All deduced rows have a boolean attribute (named  
"deduced") that is TRUE only if the row was generated by such a  
deduction.  A value of FALSE indicates that the row was original data,  
entered by a user.

When original data is modified, the triggers are responsible for  
removing any deduced rows that are now invalid and generating new rows  
that are now implied.  I would like to make it so that the only way  
that deduced rows can be deleted is through the actions of these  
triggers; I don't want a user inadvertently deleting a deduction when  
the underlying premises (the original rows that were used to generate  
the deduced rows) still imply that deduction is valid.  Users should  
only be able to manipulate the original data.

I can create a trigger that will prevent deletion of deduced rows  
easily enough, but I'm not sure how to let rows targeted for deletion  
by these deduction triggers through.  Is there a way to pass some sort  
of state indicator into a trigger?  Is this at all possible?

Thanks in advance,
Chris