Indexing of Documents An inverted index maps each keyword Ki to a set of documents S;that contain the keyword Documents identified by identifiers Inverted index may record Keyword locations within document to allow proximity based ranking Counts of number of occurrences of keyword to compute TF and operation:Finds documents that contain all of K1,K2,...,Kn. Intersection S∩S2∩..∩Sn or operation:documents that contain at least one of K1,K2,...,K union,S1∩S2∩..∩Sn,. Each S;is kept sorted to allow efficient intersection/union by merging "not"can also be efficiently implemented by merging of sorted lists Database System Concepts-6th Edition 21.14 @Silberschatz,Korth and SudarshanDatabase System Concepts - 6 21.14 ©Silberschatz, Korth and Sudarshan th Edition Indexing of Documents An inverted index maps each keyword Ki to a set of documents Si that contain the keyword Documents identified by identifiers Inverted index may record Keyword locations within document to allow proximity based ranking Counts of number of occurrences of keyword to compute TF and operation: Finds documents that contain all of K1 , K2 , ..., Kn . Intersection S1 S2 .....  Sn or operation: documents that contain at least one of K1 , K2 , …, Kn union, S1 S2 .....  Sn ,. Each Si is kept sorted to allow efficient intersection/union by merging “not” can also be efficiently implemented by merging of sorted lists