“…Another motivation to this paper is the connection between groupoids and Frobenius objects in a dagger monoidal category. For instance, a representative example of a relational convolution algebra is the relational group algebra, a version up to equivalence, of the group algebra of a group G. Group algebras are particular cases of Frobenius algebras, so relational convolution algebras provide a new class of examples of Frobenius objects in the category of sets and relations, which are also in correspondence with groupoids [28,32]. In a work in preparation [21], we study Frobenius objects arising from groupoids in the category of spans, via simplicial sets.…”