WDM 22: Phrase Query Using Positional Index

[@yiyu9519]

this video is correlated to last video. Mainly focus on the case of phrase. There are three methods to deal with it: 1. use biword. For extended word, biword AND biword. demerit: cost much memory, not such much memory to save so many phrase. 2. use positional index. demerit: cost much time to match. .3. combine this two ways and do tradeoff.