Substring index

A substring index is a data structure which gives substring search in a text or text collection in sublinear time. If you have a document $S$ of length $n$, or a set of documents $D=\{S^{1},S^{2},\dots ,S^{d}\}$ of total length $n$, you can locate all occurences of a pattern $P$ in $o(n)$ time. ($o(n)$ means less than $O(n)$. See Big O notation.)

The phrase full-text index is also often used for an index of all substrings of a text. But is ambiguous, as it is also used for regular word indexes such as inverted files and signature files. See full text search.

Substring indexes include:

• Suffix tree
• Suffix array
• N-gram index, an inverted file for all N-grams of the text