Index Compression - Slides (2011)-计算机科学

V.2 Index CompressionHeap’s law (empirically observed and postulated):Size of the vocabulary (distinct terms) in a corpus  n]corpusintermsdistinct[E with total number of term occurrences n, and constants ,  ( < 1),classically 20, 0.5 (→ ~ 3 Mio terms for 20 Bio docs)Zipf’s law (empirically observed and postulated):Relative frequencies of terms in the corpus     k xfreqrelhastermpopularmostkPth 1 ]..[with parameter , classically set to 1 Both laws strongly suggest opportuni