Index Compression Dictionary Compression Space for dictionary as a string 4 bytes per term for freq I Now avg.11 4 bytes per term for pointer to Postings. bytes/term 3 bytes per term pointer not 20 Avg. 8 bytes per term in term string 400K terms x 19=7.6 mB against 112MB for fixed width) 22Index Compression 22 Space for dictionary as a string ▪ 4 bytes per term for Freq. ▪ 4 bytes per term for pointer to Postings. ▪ 3 bytes per term pointer ▪ Avg. 8 bytes per term in term string ▪ 400K terms x 19  7.6 MB (against 11.2MB for fixed width)  Now avg. 11  bytes/term,  not 20. Dictionary Compression