One or more computers may close a purchase order by use of rules. Certain embodiments use values of attributes of a line in a purchase order (PO) to identify a rule among multiple rules. The PO line's attributes which are used to identify the rule are internal to a buyer. When the rule which is identified is disabled, the line is retained unchanged in the purchase order. When the identified rule is not disabled, a user-specified logic which is identified in the rule is used to determine a new value of a numeric term, the numeric term having a preexisting value previously agreed upon by the buyer and the seller, e.g. in units of quantity or units of money. Subsequently, an indication of the line being changed in the purchase order is transmitted to the seller. User may specify different logics in different sets of rules, for different business units.