Estévez and Nordlund (2025): Borgatti and Everett (2000) proposed a model for core-periphery relations that has become the standard. However, it has two problems: have it handles inter-categorical ties, and have it defines the ideal core as a complete block.
Estévez and Nordlund (2025): Borgatti and Everett offer two options for dealing with inter-categorical ties: disregard them and focus only on intra-categorical ties (more practical); or specify desired densities for inter-categorical blocks (more comprehensive but impractical and difficult to implement).
Estévez and Nordlund (2025): The second problem is that requiring the ideal core to be fully connected is too stringent: most networks don't meet the requirement.