Regarding the user's familiarity with the target concept, in absence of user data we approximate it by the popularity of the target concept computed as the normalized node degree as pop(c) = log(D(c)) log(|V |−1) , where D(c) denotes the number of neighbors of concept c. Formally, given the relation s p −→ o, the accessibility scores of its endpoints s and o are computed as shown in Formula 2.
although the edges of the KG are directed, activation can flow in both directions over the same edge.