What Does 'Big Data' Mean?

big data can mean one of four things:

Big Volume, Small Analytics

Big Volume, Big Analytics

Big velocity

Big variety

The ETL methodology that has emerged is: For each data source to be integrated # 针对新数据源

This (very widely used) methodology has a number of disadvantages:

#note: 预先定义好global schema应该是技术上最大的问题.