The huge growth in the data storing and the wide use of social networks and applications that depend mainly on complicated and interrelated relations between entities which need specific models of databases to store and retriev quickly and effectivel
y, the relational databases are no longer adequate in distributed systems and websites that deal with big data which have to be accessible and operable.
This paper explains briefly the challenges of relational databases and the reasons that led to emergence the non-relational databases (NoSQL), in addition to CAP theorem and some of NoSQL types, specially GraphQL
