Big data is the popular term used in the current era for extracting knowledge from large datasets. Big data is the collection of large and complex dataset. The challenge in big data is Volume, Variety and Velocity (3V's).variety can be classified into structured, unstructured data and semi structured. Structured data are the identifiable data, which is organized in some structure. Data stored in the relational database are example of structured data. Unstructured data are the data without identifiable structure, audio, video and images are few examples.