I'm talking about the general category of everything built atop BW-Tree and the Deuteronomy architecture. Murat Demirbas's blog has nice summaries of the papers. CosmosDB is a brand that encompasses more than one database engine, but I used that term as most people aren't familiar with the literature on the topic.

Foreign key constraints are not practical for distributed data stores. And are actually more controversial than you’d think for regular databases, due to their heavy performance cost.