I only talked about the network model briefly because this model has had such a brief history in database history. The hierarchical model had many inefficiencies. The network model attempted to resolve some of these deficiencies. The primary difference between the network and the hierarchical models is that the hierarchical model represents data as a tree, where each record can have only one parent, but many children. In the network model, data can have many parents and many children. But in the network model, those relationships had to be predefined.
The network model was replaced by the relational model. As with the network model, the relational model lets a piece of data have many parents and many children. But the relational model is much more flexible, primarily because the relationships do not have to be predefined (although they often are).