Persistence

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.

Integration at the database level

bounded context MUST NOT integrate on a database level. This means they will not be sharing a database at all. This removes friction in development and makes it easier to build each bounded context without having to worry about the other.

Relational vs Non Relational

Traditionally we tend to model everything relationally, while most data is not necessarily relational in nature. There is no point in bringing the complexity of a relational database and the need to use things like mapping to one using object relational mapping libraries, unless the data is in fact relational.

Polyglot

The different data storage technologies out there have different characteristics and serve different purposes. This means that is quite ok to select a specific storage mechanism per feature within a bounded context. Since we have the luxury of being event driven and have an event store, we can also allow duplicates in the data - meaning that we could have multiple representations of the same data. The truth in the system comes from the event store.

What can we use

Type	On Premise	Cloud
Documents	MongoDB	CosmosDB w/MongoDB interface
Relational	SQL for Linux	SQL PaaS - Azure
Search Index	Elastic Search	Azure Search (Elastic based)
Graph	Neo4j w/ Gremlin	CosmosDB w/Gremlin