debug label
change chapter labels
use subcaption package
chapter: intro
subfigure label setting
chapter: category
chapter: design issue
chapter: O-I-P model
chapter data input
chapter: process stage
chapter: output
use subcaptionbox
chapter: collaborative filtering
chapter: memory-based cf
chapter: model-based cf
chapter: hybrid collaborative filtering
chapter: content-bsed filtering
chapter: hybrid method
chapter: privacy
chapter: shilling attack