1. Relational databases are based on strict relational database theory, but in the face of challenges from existing e-commerce and SNS website businesses, scalability and performance cannot be effectively addressed
  2. Key Value Database No SQL database, such as Google’s Big Table, solves the shortcomings of relational databases, but based on key values, it cannot be queried like SQL. Because the data is unstructured and discrete.  
  3. Document oriented databases such as MongoDB, supporting queries
  4. It is said that there are already manufacturer products that support graph databases for nodes and edges