There are three competing technologies in use for text search. A search through the source documents for a particular keyword or phrase is initiated for each request. This method is very simple to implement but is totally unusable for large stores of information. Some low cost PC packages employ this method. The inverted index is popular today but has a major drawback in that the documents and the query statement must be correct or a keyword will not be found.
Some users employ a table of frequently misspelled words to assist the query function.
This table will not compensate for the random errors introduced by an OCR process. An N-gram is a sub partition of a word. By reducing the dependence upon complete words, a higher probability of finding association between query and source is achieved. An interesting implementation of N-gram search has been produced utilizing neural networking technology. The index of patterns is stored for later comparison in a manner similar to what psychologists believe the human brain remembers facts.