data gets replicated, because now there is a clearly identifiable unit of data whose consistency is self-contained. Another consideration is that reading and writing a single document in such databases will require a single transaction - which can be an important consideration in a Microservices architecture. In such situations, often, portions of the document are retrieved from other services via an API and stored locally for efficiency reasons. If the data units were to be split out across the services, then a read (or write) to support a service consumer might require more than one service calls, and this could result in management of multiple transactions, which may not be preferred. Conceptual schema Physical design The physical design of the database specifies the physical configuration of the database on the storage media. This includes detailed specification of data elements, data types, indexing options and other parameters residing in the DBMS data dictionary. It is the detailed design of a system that includes modules & the database's hardware & software specifications of the system. Some aspects that are addressed at the physical layer: Security - end-user, as well as administrative security. Replication - what pieces of data get copied over into another database, and how often. Are there multiple-masters, or a single one? High-availability - whether the configuration is active-passive, or active-active, the topology, coordination scheme, reliability targets, etc all have to be defined. Partitioning - if the database is distributed, then for a single entity, how is the data distributed amongst all the partitions of the database, and how is partition failure taken into account. Backup and restore schemes. At the application level, other aspects of the physical design can include the need to define stored procedures, or materialized query views, OLAP cubes, etc. See also References Further reading S. Lightstone, T. Teorey, T. Nadeau, “Physical Database Design: the database professional's guide to exploiting indexes, views, storage, and more”, Morgan Kaufmann Press, 2007. M. Hernandez, "Database Design for Mere Mortals: A Hands-On Guide to Relational Database Design", 3rd Edition, Addison-Wesley Professional, 2013. External links Database Normalization Basics by Mike Chapple (About.com) Database Normalization Intro, Part 2 Databases Database management systems Database theory