A network with two types of nodes is called 2-mode, bimodal, or bipartite. We can add more, making it multimodal. Publishers, topics, you-name-it. We can even add seemingly unrelated node-types, like academic conferences, or colors of the rainbow. The list goes on. We would have a new list for each new variety of node. Presumably we could continue adding nodes and node-types until we run out of stuff in the universe. This would be a bad idea, and not just because it would take more time, energy, and hard-drives than could ever possibly exist. As it stands now, network science is ill-equipped to deal with multimodal networks. 2-mode networks are difficult enough to work with, but once you get to three or more varieties of nodes, most algorithms used in network analysis simply do not work. It’s not that they can’t work; it’s just that most algorithms were only created to deal with networks with one variety of node.