sentences:  In general, an attribute-value system may contain any kind of data, numeric or otherwise.An attribute-value system is distinguished from a simple "feature list" representation in that each feature in an attribute-value system may possess a range of values (e.g., feature formula_1 below, which has domain of {0,1,2}), rather than simply being "present" or "absent" .Attribute-value systems are pervasive throughout many different literatures, and have been discussed under many different names