Excellent overview of NoSQL databases, data stores here including a diagram that makes it easier toÂ visualizeÂ what is happening.
In brief the author classifies them as follows
- Relato joins (joins must be handled within your application). Obviously, they store data by column as oppoional systems are the databases we’ve been using for a while now. RDBMSs and systems that support ACIDity and joins are considered relational.
- Key-value systems basically support get, put, and delete operations based on a primary key.
- Column-oriented systems still use tables but have nsed to traditional row-oriented databases. This makes aggregations much easier.
- Document-oriented systems store structured “documents” such as JSON or XML but have no joins (joins must be handled within your application). It’s very easy to map data from object-oriented software to these systems.