Also I think that the study of categorisation is very much part of DH, and a demanding and exciting one at that. My colleagues at UCLDIS who study classification theory in the context of Libraries would certainly agree. It's ironic that they are suddenly very much in demand in this digital age: what used to be considered dry and old fashioned is suddenly cool. What could be more cutting edge than ontologies, linked data and semantic tagging after all, and what underlies all this is an understanding of the theory of categorisation that you discuss here.