Hmmm. Just stumbled across United States Patent Application 0030033296 which claims:
Methods and apparatus for managing, finding and displaying objects such as digital images. Objects are tagged ("associated") with descriptive textual and numeric data ("metadata"), and stored in a relational database from which they can be selected, sorted, and found. Tags can be defined by name, tag type, and associated attributes. Objects can be tagged by dropping a tag onto the object, or relating a database record for the tag to a database record for the object. Tagged objects can be searched for and displayed according to the degree to which their metadata matches the search criteria. Visual cues can indicate whether displayed objects match all, some but not all, or none of the search criteria. Database object distributions can be displayed as histograms or scatter plots, including timelines, calendars or maps. Object distributions can be used to search for objects or to limit search results for a previous search.