Dimension specification refers to reducing the dimension in data, that is, reducing the characteristics or attributes of data to reduce the complexity and storage requirements of data. Size specification can be realized by feature selection or feature extraction. Quantitative specification refers to reducing the number of data, that is, reducing the number of samples or observations of data. Quantity specification can be achieved by sampling or filtering. The goals of size specifications and quantity specifications are also different. The goal of dimension specification is to reduce the complexity and storage requirements of data in order to better understand and analyze data. The goal of quantity specification is to reduce the size of data, so as to improve the calculation efficiency and reduce the calculation cost when dealing with big data.