1. A computer-implemented method for updating a concept-mapping function that facilitates evaluating a qualitative search term applied to an attribute during query processing, the method comprising: extracting a value for the attribute from each data item in a set of data items; and updating the concept-mapping function based on the extracted attribute values, wherein the concept-mapping function associates a given value for the attribute with a numerical compatibility index that indicates a compatibility between the given value and the qualitative search term as applied to the attribute, wherein the qualitative search term comprises one or more words that express a quality of the attribute value; wherein updating the concept-mapping function comprises, determining boundaries for the concept-mapping function based the extracted attribute values, and within the determined boundaries, using a pre-specified distribution to update the concept-mapping function; and wherein determining the boundaries for the concept-mapping function includes: computing a mean attribute value and a standard deviation for the extracted attribute values; and using the mean attribute value and the standard deviation to determine the boundaries for the concept-mapping.