1. A data enrichment system comprising: an attribute relevance module, executed by at least one hardware processor, to measure relevance of an attribute to a data object to be enriched, the data object including the attribute including one of a known and an unknown value, wherein the relevance of the attribute includes a determination of a unique association of the attribute with the data object, and a determination of a discriminative property of the attribute with respect to instances of the data object based on evaluation of an entropy of a predetermined number of past values of the attribute; and an output value confidence module, executed by the at least one hardware processor, to determine a confidence of a source based on utility of an output value of the source used for enrichment of the data object, the output value representing at least one of the known and unknown values of the attribute, wherein the system uses the measured relevance of the attribute and the determined confidence of the source to determine assignment of the unknown value to the attribute.