Table 1. Typical pattern of knowledge evolution (source: Di Caro et al. 2017 [59]).

(a)	Stability	a cluster A exists at time t and t+1
(b)	Birth	the cluster A at time t+1 has no antecedent at time t
(c)	Death	the cluster A at time t disappears at time t+1
(d)	Merging	multiple clusters at time t combine in a new topic A at time t+1
(e)	Splitting	multiple clusters at time t+1 share an antecedent at time t