1. A method comprising: accessing descriptors in metadata descriptive of a first item and of a second item, the descriptors and metadata having a metadata type that corresponds to a metadata model that organizes the descriptors into multiple tiers of the metadata model, the descriptors including a first descriptor of the first item and a second descriptor of the second item, the first descriptor and the second descriptor being represented in a tier among the multiple tiers of the metadata model; determining that the first descriptor and the second descriptor are members of a cluster of descriptors based on the tier within which the first descriptor and the second descriptor are represented in the metadata model, the determining being performed by a processor of a machine; and generating a user profile based on the cluster of descriptors of which the first descriptor and the second descriptor are members.