Indexing by words is suitable when a system should process documents with few or no typing or grammatical errors and if the documents have been translated in a language that is known to the system (necessary for stemming/ decompounding). If this is not the case, the system can break down words into smaller units ("N-Gram"), which makes error-tolerant comparison possible.

An n-gram is a sub-sequence of n items from a given sequence. n-grams are used in various areas of statistical natural language processing and genetic sequence analysis. The items in question can be letters, words or base pairs according to the application.