Couchbase says " Interactive software has changed in fundamental ways over the last 35 years. But until recently, database technology has not advanced to keep pace. The “online” systems of the 1970s have evolved into today’s web and mobile applications. These systems solve new problems for vastly larger user populations, and they execute atop a computing infrastructure that has changed even more radically over the years. NoSQL database technologies have emerged to enable the cost-effective management of data behind modern web and mobile applications. Here a complete details about need for and framework of NoSQL
For more general treatment of topic see here for wikipedia article on NoSQL.