“…The adoption of KGđť‘ as a source of side-information has generated several advancements in the tasks of recommendation [16], knowledge completion [33], preference elicitation [14], user modeling [69], and thus produced a vast literature. In recent years, the Knowledgeaware Recommender Systems have been particularly impactful for several recommendation tasks: hybrid collaborative/contentbased recommendation [16,47], exploiting the KG information to suffice the lack of collaborative information and to improve the performance; knowledge-transfer, cross-domain recommendation [29,41,77], where the KGđť‘ allow to find semantic similarities between different domains; interpretable/explainablerecommendation [6,13,16,73,76], with KG being a backbone for understanding the recommendation model and providing humanlike explanations; user-modeling [39,50,54,69], since the resource descriptions can drive the construction of the user profile; graphbased recommendation [27,61,62,68,70,71], where the topologybased techniques have met the semantics of the edges/relations, and the ontological classification of nodes (classes); the cold-start problem [29,51,60,74], since the KGđť‘ can overcome the lack of collaborative information; the content-based recommendation [15,53] that solely relies on KG and still produces high-quality recommendations. KGFlex could be considered a Knowledge-aware hybrid collaborative/content-based recommendation model.…”