JP2002269096A - Method and device for character string restoration and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the storage capacity needed for character string retrieval using a suffix array. SOLUTION: A character string is restored by using the suffix array of the character string and a character table containing positions in the suffix array by the characters in the character string. Basically, the total storage capacity is reduced by storing a suffix array of a character string and a character table mentioned below instead of the suffix array of the character string and the character table and restoring the character string from the suffix array and character table when character string retrieval is performed. For the purpose, the device is equipped with a character string buffer which stores the character string, a suffix array buffer which stores the suffix array of the character string, a character table buffer which stores the positions in the suffix array by the characters in the character string, and a character string restoration part which refers to the character table buffer and suffix array buffer and stores the characters at specific positions in the character string buffer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a character string restoring method in which a character string is restored using a suffix array of a character string and a character table storing the position in the suffix array for each character in the character string. The present invention relates to a method, an apparatus thereof, and a recording medium.

[0002]

2. Description of the Related Art Conventionally, Japanese Patent Application Laid-Open No. H10-260980 discloses a technique for searching a text as a compressed code string.
It describes that the basic processing is to match the prefix (prefix) of the search key with the suffix (suffix) in the text. U.S.A. Manber and
G. FIG. Myers, “Suffix arrays: a
new method for on-line st
ring searches ”, SIAM jouna
l of computing, 22 (5), p
p. 935-948, 1993 include Suffix
Proposal of array (suffix array). Suffix arr
The algorithm for the construction and use of ay is shown.

For a text T and an input pattern P, T
The problem of finding the position of occurrence in a string is string matching (string
g matching). When T is known, high-speed character string collation can be realized by constructing and using an index in advance for T.

As an example of such an index, a suffix array (su
fix array has been proposed (U. Man).
ber and G. Myers 1993). An example of the suffix sequence is shown below for the case where the text T = BANANA.

[0005]

The text is provided with a symbol ＄ indicating the end of the text. The suffix is a character string ranging from each character in the text to the end of the text, and N suffixes can be defined for a text consisting of N characters. The appearance position of the first character of the suffix in the text has a one-to-one correspondence. This appearance position is called a pointer. The suffix array is a pointer sequence obtained by arranging all the pointers such that the suffixes to the pointers are in dictionary order. Here, the dictionary order of the suffix is a character constituting the suffix (referred to as a suffix constituent character).
Is defined based on a character value defined in advance.
In this description, the character value of each character is determined as follows.

＄ <＄ <A <B <N Therefore, the following suffix arrangement is obtained from the above example.

Suffix array: 5 3 1 0 4 2 For example, the suffix corresponding to the first pointer 5 is A #, and is younger in dictionary order than the suffix ANA # corresponding to the pointer 3.

The appearance position of P in T can be obtained by a binary search on the above suffix array. That is, P
The pointers to the suffixes prefixed by are the appearance positions of P in T, and those pointers are continuously arranged in the suffix array. Therefore, the continuous range may be obtained by a binary search. Although not related to suffix sequences, this type of search is disclosed in
It is also found in -260980.

[0010]

Conventionally, when performing a character string search using a suffix array, it is necessary to store (A) a suffix array of character strings and (B) a character string. As the number of strings increases, these storage costs become a practical problem.

An object of the present invention is to reduce the amount of storage required for a character string search using a suffix array.

[0012]

Means for Solving the Problems Basically, (A)
Instead of (B), the following (A) and (C) are stored, and (A) and (B) are restored from (A) and (C) at the time of executing a character string search, thereby reducing the total storage amount. . (A) Character string suffix array (C) Character table

Specifically, means for achieving the object include a character string buffer for storing a character string, a suffix array buffer for storing a suffix array of character strings, and a suffix array buffer for storing each character in the character string. It comprises a character table buffer that stores the position in the suffix array, and a character string restoration unit that stores characters at a predetermined position in the character string buffer with reference to the character table buffer and the suffix array buffer.

[0014]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an example of the configuration of the apparatus, and FIG. 2 shows an example of the software.

In the above example, the suffix array for the character string "BANANA" is as shown in FIG. The upper part of FIG. 3 clearly shows the element position (array subscript) of the suffix array, and the lower part shows the value of each element (pointer) of the suffix array.

It is assumed that a character table shown in FIG. 4 is prepared for the suffix arrangement shown in FIG. In FIG. 4, the character codes of the characters appearing in the character string are stored in the left column (character code column) in the dictionary order of the characters. Last"#"
The line is provided to represent the last line of the character table.

On the other hand, in the right column (array subscript column), for each character code, a pointer to the youngest suffix starting from that character in dictionary order (that is, "A" is 5, "B" The array suffix in the suffix array in which "0" is stored for "" and 4) is stored for "N" is stored.

The suffix arrangement of FIG. 3 and the character table of FIG.
It is assumed that the data is stored in the suffix array buffer and the character table buffer.

The character string restoring section converts the character string "BA" from the character table and the suffix array according to the flowchart shown in FIG.
NANA "is restored. However, the character code of the first row of the character table is changed to table [I] .c.
ode and the array subscript is table [I]. index
Expressed by The element of the suffix array for the array suffix P is represented by A [P]. The character string buffer element corresponding to the array subscript P is S [P]
Expressed by After this processing is completed, the character string buffer S [. . ] Is restored.

[0020]

The character table is independent of the capacity of the target character string.
Different characters require only a few minutes of storage. Therefore,
When the target character string is large, storing the character table can reduce the storage amount as a whole, rather than storing the target character string.

When a character string search becomes necessary, the character string is restored by the character string restoring unit. This processing is performed only once by scanning the suffix array, and can be performed at a very high speed. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a hardware configuration according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of the software.

FIG. 3 is an array diagram showing an example of a suffix array.

FIG. 4 is an array diagram showing a character table for a suffix array.

FIG. 5 is a flowchart illustrating processing of a character string restoring unit.

Claims (3)

[Claims] 1. A character string restoring method for restoring a character string by using a character string suffix array and a character table in which a position in the suffix array is stored for each character in the character string. 2. A character string buffer for storing a character string, a suffix array buffer for storing a suffix array of character strings, and a character table for storing a position in the suffix array for each character in the character string. A character string restoring device comprising: a buffer; and a character string restoring unit that refers to the character table buffer and the suffix array buffer and stores characters at predetermined positions in the character string buffer. 3. A computer-readable storage medium storing a program for restoring a character string using a character table storing a character string suffix array and a position in the suffix array for each character in the character string.