Inverted index
Inverted table in word or words for the keyword index, corresponding to the recorded entry records the emergence of the word or words all documents in the keyword table, a table entry is a word segment, it records that document and ID character position occurs in the document.
As the number of documents each word or phrase in the corresponding dynamic changes, so the inverted establishment and maintenance of the table are more complex, but at query time since a keyword query to get all the documents corresponding, so the efficiency is higher than the positive displacement table. In the full-text search, the search is a rapid response to the most critical performance, and as a result of indexing in the background, although the efficiency is relatively low, but does not affect the efficiency of the entire search engine.
Forward index is a mapping from the document to the keywords (known documentation requirements keyword), an inverted index is a mapping from a key to a document (known keyword seeking documents).