We demonstrate a sense in which the equivalence between blocks (subgraphs without articulation points) and biconnected components (subgraphs in which there are two edge-disjoint paths between any pair of nodes) that holds in ordinary graph theory can be generalized to hypergraphs. The result has an interpretation for relational databases that the universal relations described by acyclic join dependencies are exactly those for which the connections among attributes are defined uniquely. We also exhibit a relationship between the process of Graham reduction [6] of hypergraphs and the process of tableau reduction [1] that holds only for acyclic hypergraphs.