Imagine that you have coupons that you wanted to push to mobile customers that purchase a specific item. This is a customer facing system of engagement requires location data, purchase data, wallet data, and so on. You want to engage the mobile customer in real-time.
What you require is a very agile delivery system that is easily able to processes unstructured data. The system of engagement would need to be extremely dynamic.
A traditional database product would prefer more predictable, structured data. A relational database may require vertical and, sometimes horizontal expansion of servers, to expand as data or processing requirements grow.
An alternative, more cloud-friendly approach is to employ NoSQL.
The load is able to easily grow by distributing itself over lots of ordinary, and cheap, Intel-based servers. A NoSQL database is exactly the type of database that can handle the sort of unstructured, messy and unpredictable data that our system of engagement requires.
NoSQL is a whole new way of thinking about a database. NoSQL is not a relational database. The reality is that a relational database model may not be the best solution for all situations. The easiest way to think of NoSQL, is that of a database which does not adhering to the traditional relational database management system (RDMS) structure. Sometimes you will also see it revered to as 'not only SQL'.
It is not built on tables and does not employ SQL to manipulate data. It also may not provide full ACID (atomicity, consistency, isolation, durability) guarantees, but still has a distributed and fault tolerant architecture.
The NoSQL taxonomy supports key-value stores, document store, BigTable, and graph databases.
MongoDB, for example, uses a document model, which can be thought of as a row in a RDBMS. Documents, a set of fields (key-value pairs) map nicely to programming language data types. A MongoDB database holds a collection which is a set of documents. Embedded documents and arrays reduce need for joins, which is key for high performance and speed.
Why NoSQL? It's high performance with high availability, and offers rich query language and easy scalability.