The popularity of NoSQL database systems is rapidly increasing, especially to support nextgenerationweb applications. However, given the high heterogeneity existing in this world,where more than fifty systems are available, database design is usually based on best practicesand guidelines which are strictly related to the selected system.We propose a database design methodology for NoSQL systems with initial activities thatare independent of the specific target system. The approach is based on NoAM (NoSQL AbstractModel), a novel abstract data model for NoSQL databases, which exploits the commonalitiesof various NoSQL systems and is used to specify a system-independent representationof the application data. We show how this intermediate representation can be implemented intarget NoSQL databases, taking into account their specific features.Overall, the methodology aims at supporting scalability, performance, and consistency, asneeded by next-generation web applications.