The paper discusses the challenges of faceted vocabulary organization in universal classifications which treat the universe of knowledge as a coherent whole and in which the concepts and subjects in different disciplines are shared, related and combined. The authors illustrate the challenges of the facet analytical approach using, as an example, the revision of class 72 in UDC. The paper reports on the research undertaken in 2013 as preparation for the revision. This consisted of analysis of concept organization in the UDC schedules in comparison with the Art & Architecture Thesaurus and class W of the Bliss Bibliographic Classification. The paper illustrates how such research can contribute to a better understanding of the field and may lead to improvements in the facet structure of this segment of the UDC vocabulary.