Document retrieval

Document retrieval is the task of matching a stated user query against a set of free-text records, which may be newspaper articles, real estate records, paragraphs in a manual or any other mostly unstructured text. Queries range from a few words to multi-sentence descriptions of an information need. A document retrieval system consists of a database of documents, a classification algorithm that builds a full text index, and a user interface for reaching the database. It has two main tasks: finding the documents relevant to a query, and ranking the matches by relevance with algorithms such as PageRank. The problem is treated as a branch of text retrieval and of information retrieval, and it is the basis of internet search engines. Indexing is either form based, which matches exact syntactic properties as suffix tree indexing does, or content based, which uses semantic connections and most often an inverted index.