A case based reasoning system and method for matching a problem case to at least one solved case. A solved case database stores solved case data correlated to a plurality of solved cases. An attribute database stores a set of attributes and observation cost data corresponding to each of the attributes, such that the observation cost data corresponding to an attribute is correlated to a cost of determining an attribute value corresponding to the attribute. A set of potential solved cases is determined. A set of relevant attributes for which at least one potential solved case has an attribute value and for which no corresponding problem attribute value has been input is determined and ranked based on the observation cost data for each relevant attribute.