Examples of graph Gotu for three types of OTUs, from top to bottom: (i) ideal OTU, which is single and a clique (each read has a dissimilarity smaller than the barcoding gap with all the other reads of the OTU; (ii) a single OTU with a large strongly connected core entity and some satellite nodes; (iii) a composed OTU, consisting of several entities with high intra-entity connections rates and low between entities connection rates (and some satellite nodes as well).