Hypercore decomposition for non-fragile hyperedges: concepts, algorithms, observations, and applications

Hypergraphs are a powerful abstraction for modeling high-order relations, which are ubiquitous in many fields. A hypergraph consists of nodes and hyperedges (i.e., subsets of nodes); and there have been a number of attempts to extend the notion of k -cores, which proved useful with numerous applications for pairwise graphs, to hypergraphs. However, the previous extensions are based on an unrealistic assumption that hyperedges are fragile , i.e., a high-order relation becomes obsolete as soon as a single member leaves it.In this work, we propose a new substructure model, called (k,t) -hypercore, based on the assumption that high-order relations remain as long as at least t fraction of the members remains. Specifically, it is defined as the maximal subhypergraph where (1) every node is contained in at least k hyperedges in it and (2) at least t fraction of the nodes remain in every hyperedge. We first prove that, given t (or k ), finding the (k,t) -hypercore for every possible k (or t ) can be computed in time linear w.r.t the sum of the sizes of hyperedges. Then, we demonstrate that real-world hypergraphs from the same domain share similar (k,t) -hypercore structures, which capture different perspectives depending on t . Lastly, we show the successful applications of our model in identifying influential nodes, dense substructures, and vulnerability in hypergraphs.