The paper presents a database system called PNUTS. PNUTS offers a service with slightly stronger semantics than the models seen before such as Bigtable and Dynamo but still way simpler than a full relational database. PNUTS has relational tables, but accepts queries only on individual tables. The consistency model of PNUTS can be stronger than eventual consistency, and the API enables the user to specify the model of read consistency desired (I think this is a nice feature). However, the consistency model is weaker than serializable transactions.
A key architectural component of PNUTS is a pub-sub system, used to ensure reliability and replication. PNUTS uses a proprietary message broker, and updates are considered committed when they have been published to the message broker.