1. A document management and retrieval system, comprising: (a) one or more processors; and (b) a non-transitory storage medium coupled to the one or more processors and containing instructions executable by the one or more processors such that when the instructions are executed on the one or more processors, one or more of the processors will: store appearance positions for a plurality of words in one or more of a plurality of documents in a word index store; store a plurality of tag indexes and an appearance position of the character string associated with each tag in a set of documents in a tag index store, each tag index being associated with a respective character string and comprising: a tag associated with its respective character string in one of the plurality of documents, the tag having a name and indicating attributes of the character string based upon the meaning of the character string; at least one of a right word string comprising one or more adjacent words that appears to the right of its respective character string and a left word string comprising one or more adjacent words that appears to the left of its respective character string; a combination of the tag with at least one of the left and right word strings; and operate as a document retrieval unit that receives as a search query an input of a phrase containing a search tag name and a search word, and returns a list of identified documents that contain the phrase by utilizing the combination entries stored in the tag index store; operate as a tag update unit that interprets a query for associating or disassociating a tag to or from a character string in a document and updates the associated tag index stored in the tag index store; and operate as a document index creating unit that updates a word index within the word index store when one or more documents are identified; and (c) a bit string store that stores a plurality of a bit strings, each bit string representing a set of documents of the plurality of documents that contain a high-frequency word or a set of documents that contain a specified tag, wherein: the tag update unit updating a bit string in the bit string store when a tag is associated or disassociated to or from a character string in a document; and the document retrieval unit using the high-frequency word and tag name contained in a query to refer to the bit string store prior to a search and to obtain a set of documents that contain all high-frequency words and tag names in the query.
1. A document management and retrieval system, comprising: (a) one or more processors; and (b) a non-transitory storage medium coupled to the one or more processors and containing instructions executable by the one or more processors such that when the instructions are executed on the one or more processors, one or more of the processors will: store appearance positions for a plurality of words in one or more of a plurality of documents in a word index store; store a plurality of tag indexes and an appearance position of the character string associated with each tag in a set of documents in a tag index store, each tag index being associated with a respective character string and comprising: a tag associated with its respective character string in one of the plurality of documents, the tag having a name and indicating attributes of the character string based upon the meaning of the character string; at least one of a right word string comprising one or more adjacent words that appears to the right of its respective character string and a left word string comprising one or more adjacent words that appears to the left of its respective character string; a combination of the tag with at least one of the left and right word strings; and operate as a document retrieval unit that receives as a search query an input of a phrase containing a search tag name and a search word, and returns a list of identified documents that contain the phrase by utilizing the combination entries stored in the tag index store; operate as a tag update unit that interprets a query for associating or disassociating a tag to or from a character string in a document and updates the associated tag index stored in the tag index store; and operate as a document index creating unit that updates a word index within the word index store when one or more documents are identified; and (c) a bit string store that stores a plurality of a bit strings, each bit string representing a set of documents of the plurality of documents that contain a high-frequency word or a set of documents that contain a specified tag, wherein: the tag update unit updating a bit string in the bit string store when a tag is associated or disassociated to or from a character string in a document; and the document retrieval unit using the high-frequency word and tag name contained in a query to refer to the bit string store prior to a search and to obtain a set of documents that contain all high-frequency words and tag names in the query. 2. The document management and retrieval system according to claim 1 , further comprising a quick tag value determining unit that uses an arbitrary character string to enable quick reference to a set of tag names associated with the arbitrary character string, wherein: the tag update unit includes means for updating data in the quick tag value determining unit when a tag is associated with its respective character string; and the document retrieval unit includes means for referring to the quick tag value determining unit and the tag index store to execute a search when a phrase containing search tag names that appear in succession is input as a search query.