1. A computer-implemented method for maintaining data, the method comprising: at a first computer system, receiving a cleansing case associating a source instance of a data element having one or more associated attribute values with a target instance of a data element; permitting a first user at the first computer system to process the cleansing case by permitting the first user to identify one or more attribute values associated with the source instance that are to be associated with the target instance, and associate the identified attribute values with the target instance; and after the first user processes the cleansing case, permitting a second user at a second computer system to process the cleansing case by permitting the second user to identify one or more attribute values associated with the source instance that are to be associated with the target instance, and associate the identified attribute values with the target instance.