How does an inverted index reduce storage requirements?
I think the author meant that by separating the index into the &quot;dictionary&quot; part and the &quot;postings&quot; part, we reduce the storage requirements of the strings themselves, because now we only have to store one string for each unique word. It's as if you are storing the vocabulary of the language itself, independent from the documents. It is also mentioned later that the dictionary is usually kept in memory, so it is important to make sure it doesn't take up much space.