Apparatus and method for compressing texts

Claims

What is claimed is:

1. A text file compressing apparatus comprising:

word detecting means for detecting words in sentences comprising a text file;

representative word storage means for classifying a plurality of words into a plurality of sets of synonymous words and to store the sets with a representative word for each set;

representative word retrieval means for retrieving the representative words for the detected words from their respective sets in said representative word storage means;

representative word rewrite means for rewriting the detected words into the retrieved representative words; and

coding means for coding the text file after the detected words are rewritten by said representative word rewrite means.

2. The text file compressing apparatus of claim 1, wherein said coding means includes:

correspondence table storage means for storing a correspondence table showing a relation between a plurality of words and string of bits; and

string-of-bits conversion means for converting each detected word in the text file into the string of bits after the detected words are rewritten into the representative words by said representative word rewrite means.

3. The text file compressing apparatus of claim 2, wherein:

the strings of bits in said correspondence table are variable; and

the representative word in each set is assigned a shortest string of bits compared with other words in the set.

4. The text file compressing apparatus of claim 3, wherein words with high probabilities with which the words appear in the texts are assigned short strings of bits, and words with small probabilities are assigned long strings of bits.

5. The text file compressing apparatus of claim 2, wherein words with high probabilities with which the words appear in the texts are assigned short strings of bits, and words with small probabilities are assigned long strings of bits.

6. The text file compressing apparatus of claim 1, wherein said coding means includes:

dictionary storage means for storing a dictionary including a plurality of words arranged in an order of their respective probabilities; and

string-of-bits conversion means for converting the detected words in the text file into strings of bits after the detected words are rewritten into the representative words by said representative word conversion means, said strings of bits indicating a location of each word in the dictionary.

7. The text file compressing apparatus of claim 6 further comprising:

probability computing means for detecting the words in the sentences comprising the text file to compute probabilities with which the words appear in the text; and

dictionary generation means for generating a dictionary by arranging the detected words in relation with their respective probabilities, the resulting dictionary being stored in said dictionary storage means,

whereby the text file compressing apparatus yields the text file including strings of bits, and the dictionary generated by the dictionary generating means as a result of an operation.

8. The text file compressing apparatus of claim 6, wherein the dictionary stored in said dictionary storage means is shared by a plurality of text files.

9. The text file compressing apparatus of claim 1 further comprising:

take-out means for taking out sentences separately from the text file;

structure-parse means for structure-parsing each sentence to generate an equation tree, said equation tree having a tree structure with a plurality of nodes linked one with another;

string-of-characters conversion means for converting the equation tree into strings of characters, a parent-child relation being represented by a parenthesis; and

sentence conversion means for converting each sentence taken out by said take-out means into the strings of characters, and

wherein said correspondence table storage means stores the parenthesis in relation with strings of bits,

whereby said converting means converts the parenthesis into a string of bits.

10. The text file compressing apparatus of claim 9, wherein said string-of-characters conversion means includes:

a string-of-characters buffer in which the equation tree in the form of strings of characters are arranged;

first placement means for placing a word corresponding to a parent node at a top of the equation tree, and the words corresponding to all children nodes within said string-of-character buffer, all the children nodes being parenthesized;

current node set means for making each child node into a current node in turn;

second placement means for placing a word corresponding to the current node and the words corresponding to all children nodes, all the children nodes being parenthesized; and

repetition means for repeatedly activating said second placement means for each child node.

11. A text file compressing apparatus for compressing a text file, said text file compressing apparatus comprising:

detecting means for detecting words in sentences comprising a text file;

form storage means for storing form information for a plurality of words, said form information comprising infinitives and form marks indicating forms of the words;

form information retrieval means for retrieving the form information that matches with the words detected by said detection means from said form storage means;

form information rewrite means for rewriting the words detected by said detection means into their respective form information; and

coding means for coding the text file after the words detected by said detecting means are rewritten into the representative words by said form information rewrite means.

12. The text file compressing apparatus of claim 11, wherein said coding means includes:

correspondence table storage means for storing a correspondence table showing a relation between a plurality of words and string of bits; and

string-of-bits conversion means for converting each detected word in the text file into the string of bits after the detected words are rewritten into the representative words by said representative word rewrite means.

13. The text file compressing apparatus of claim 12, wherein the infinitives are assigned shorter strings of bits compared with their different forms in said correspondence table.

14. The text file compressing apparatus of claim 13, wherein words with high probabilities with which the words appear in the texts are assigned short strings of bits, and words with small probabilities are assigned long strings of bits.

15. The text file compressing apparatus of claim 14, wherein said correspondence storage means further stores the form marks in relation with the strings of bits,

whereby said string-of-bits conversion means converts the form marks into the strings of bits.

16. The text file compressing apparatus of claim 12, wherein said coding means includes:

dictionary storage means for storing a dictionary including a plurality of words arranged in an order of their respective probabilities; and

string-of-bits conversion means for converting the detected words in the text file into strings of bits after the detected words are rewritten into the representative words by said representative word conversion means, said strings of bits indicating a location of each word in the dictionary.

17. A text file compressing apparatus comprising:

first detecting means for detecting words in sentences comprising a text file;

form storage means for storing form information for a plurality of words, said form information comprising infinitives and form marks indicating forms of the words;

form information retrieval means for retrieving the form information that matches with the words detected by said first detection means from said form storage means;

form information rewrite means for rewriting the words detected by said first detection means into their respective form information;

second detecting means for detecting words in the sentences comprising the text file;

representative word storage means for classifying a plurality of words into a plurality of sets of synonymous words to store the sets with a representative word for each set;

representative word retrieval means for retrieving the representative words for the words detected by said second detection means from their respective sets in said representative word storage means;

representative word rewrite means for rewriting the words detected by said second detection means into the retrieved representative words; and

coding means for coding the text file after the words detected by said second detection means are rewritten by said representative word rewrite means.

18. The text file compressing apparatus of claim 17, wherein said coding means includes:

correspondence table storage means for storing a correspondence table showing a relation between a plurality of words and string of bits; and

string-of-bits conversion means for converting each detected word in the text file into the string of bits after the detected words are rewritten into the representative words by said representative word rewrite means.

19. The text file compressing apparatus of claim 18, wherein:

the strings of bits in said correspondence table are variable; and

the representative word in each set is assigned a shortest string of bits compared with other words in the set and the infinitives are assigned shorter strings of bits compared with their different forms in said correspondence table.

20. The text file compressing apparatus of claim 19, wherein the representative words and infinitives with high probabilities with which the words appear in the texts are assigned short strings of bits, and words with small probabilities are assigned long strings of bits in said correspondence table.

21. The text file compressing apparatus of claim 20, wherein said correspondence storage means further stores the form marks in relation with the strings of bits,

whereby said string-of-bits conversion means converts the form marks into the strings of bits.

22. A method for compressing a text file for a text file compressing apparatus including a text file storage unit for storing text files, a representative word storage unit for classifying a plurality of words into a plurality of sets of synonymous words to store the sets with a representative word for each set, and a code information storage unit for storing code information used to code words in the text file, said method comprising the steps of:

detecting words in sentences comprising the text file;

retrieving the representative words from the sets for the detected words;

rewriting the detected words with the retrieved representative words; and

coding the text file after the detected words are rewritten into the representative words while referring to the code information in said code information storage unit.

23. The method of claim 22, wherein said coding step includes:

converting the words in the text file into string of bits after the detected words are rewritten into the representative words while referring to the code information in said code information storage unit, the code information being stored in the form of a correspondence table showing a relation between a plurality of words and strings of bits.

24. The method of claim 22, wherein said coding step includes:

converting the words in the text file into string of bits after the words are rewritten into the representative words while referring to the code information, the code information being stored in said code information storage unit in the form of a dictionary including words arranged in an order of probabilities with which the words appear in the file text, said strings of bits showing an order of each word in the code information.

25. The method of claim 24 further comprising the steps of:

detecting the words in the sentences comprising of the text file and computing probabilities with which the words appear in the text; and

generating a dictionary by arranging the detected words in relation with their respective probabilities, the resulting dictionary being stored in said code information storage unit.

26. The method of claim 22 further comprising the steps of:

taking out sentences separately from the text file;

structure-parsing each sentence and generating an equation tree, said equation tree having a tree structure with a plurality of nodes linked on with another;

converting the equation tree into strings of characters, a parent-child relation being represented by a parenthesis; and

converting each sentence taken out by said sentence taking out step into the strings of characters,

wherein said code information storage unit stores the parenthesis in relation with strings of bits,

whereby the parenthesis is converted into a string of bits in said sentence-to-string-of-characters converting step.

27. The method of claim 26, wherein said equation-tree-to-string-of-characters converting step includes:

arranging the equation tree in the form of strings of characters;

placing a word corresponding to a parent node at a top of the equation tree, and the words corresponding to all children nodes arranged in said arranging sub-step, all the children nodes being parenthesized;

making each child node into a current node in turn;

placing a word corresponding to the current node and the words corresponding to all children nodes, all the children nodes being parenthesized; and

repeating said secondly mentioned placing sub-step for each child node.

28. A method for compressing a text file for a text file compressing apparatus including a text file storage unit for storing text files, a form storage unit for storing a plurality of words in the form of infinitives and form marks specifying a form of each word, and a code information storage unit for storing code information used to code words in the text file, said method comprising the steps of:

detecting words in sentences comprising the text file;

retrieving form information that matches with the detected words from said form storage unit;

rewriting the detected words with their respective form information; and

coding the text file after the words are rewritten into the form information while referring to the code information in said code information storage unit.

29. The method of claim 28, wherein said coding step includes:

converting the words in the text file into string of bits after the detected words are rewritten into the representative words while referring to the code information in said code information storage unit, the code information being stored in the form of a correspondence table showing a relation between a plurality of words and strings of bits.

30. The method of claim 29, wherein said rewriting step includes:

rewriting the form marks in the text file into strings of bits while referring to said correspondence table, said correspondence table further showing a relation between the strings of bits and form marks.

31. A method for compressing a text file for a text file compressing apparatus including a text file storage unit for storing text files, a representative word storage unit for classifying a plurality of words into a plurality sets of synonymous words to store the sets with a representative word for each set, a form storage unit for storing a plurality of words in the form of infinitives and form marks specifying a form of each word, and a code information storage unit for storing code information used to code words in the text file, said method comprising the steps of:

detecting words in sentences comprising the text file;

retrieving form information that matches with the detected words from said form storage unit;

rewriting the detected words with the form information;

detecting words in post-rewrite sentence in the rewriting step;

retrieving the representative words for the words detected in said post-rewrite-word detecting step from the sets from said representative word storage unit;

rewriting the post-rewrite words into their respective representative words; and

coding the text file after the post-rewrite words are rewritten into their respective representative words.

32. The method of claim 31, wherein said coding step includes:

converting the words in the text file into string of bits after the detected words are rewritten into the representative words while referring to the code information in said code information storage unit, the code information being stored in the form of a correspondence table showing a relation between a plurality of words and strings of bits.

33. A text file compressing apparatus comprising:

word detecting means for detecting words in sentences comprising a text file;

representative word storage means for classifying a plurality of words into a plurality of sets of synonymous words and to store the sets with a representative word for each set;

representative word retrieval means for retrieving the representative words for the detected words from their respective sets in said representative word storage means;

representative word rewrite means for rewriting the detected words into the retrieved representative words;

coding means for coding the text file after the detected words are rewritten by said representative word rewrite means;

take-out means for taking out sentences separately from the text file;

structure-parse means for structure-parsing each sentence to generate an equation tree, said equation tree having a tree structure with a plurality of nodes linked one with another;

string-of-characters conversion means for converting the equation tree into strings of characters, a parent-child relation being represented by a parenthesis; and

sentence conversion means for converting each sentence taken out by said take-out means into the strings of characters, and

wherein said correspondence table storage means stores the parenthesis in relation with strings of bits,

whereby said converting means converts the parenthesis into a string of bits.

34. The text file compressing apparatus of claim 33, wherein said string-of-characters conversion means includes:

a string-of-characters buffer in which the equation tree in the form of strings of characters are arranged;

first placement means for placing a word corresponding to a parent node at a top of the equation tree, and the words corresponding to all children nodes within said string-of-character buffer, all the children nodes being parenthesized;

current node set means for making each child node a current node in turn;

second placement means for placing a word corresponding to the current node and the words corresponding to all children nodes, all the children nodes being parenthesized; and

repetition means for repeatedly activating said second placement means for each child node.

35. A method for compressing a text file for a text file compressing apparatus, the apparatus including a text file storage unit for storing text files, a representative word storage unit for classifying a plurality of words into a plurality of sets of synonymous words to store the sets with a representative word for each set, and a code information storage unit for storing code information used to code words in the text file, said method comprising the steps of:

detecting words in sentences comprising the text file;

retrieving the representative words from the sets for the detected words;

rewriting the detected words with the retrieved representative words;

coding the text file after the detected words are rewritten into the representative words while referring to the code information in said code information storage unit;

taking out sentences separately from the text file;

structure-parsing each sentence and generating an equation tree, said equation tree having a tree structure with a plurality of nodes linked one with another;

converting the equation tree into strings of characters, a parent-child relation being represented by a parenthesis; and

converting each sentence taken out by said sentence taking out step into the strings of characters,

wherein said code information storage unit stores the parenthesis in relation with strings of bits,

whereby the parenthesis is converted into a string of bits in said sentence-to-string-of-characters converting step.

36. The method of claim 35, wherein said equation-tree-to-string-of-characters converting step further comprises the steps of:

arranging the equation tree in the form of strings of characters;

placing a word corresponding to a parent node at a top of the equation tree, and the words corresponding to all children nodes arranged in said arranging sub-step, all the children nodes being parenthesized;

making each child node into a current node in turn;

placing a word corresponding to the current node and words corresponding to all children nodes, all the children nodes being parenthesized; and

repeating said secondly mentioned placing sub-step for each child node.

37. A text file compressing apparatus comprising:

word detecting means for detecting words in sentences comprising a text file;

representative word storage means for classifying a plurality of words into a plurality of sets of synonymous words and to store the sets with a representative word for each set;

representative word retrieval means for retrieving the representative words for the detected words from their respective sets in said representative word storage means;

representative word rewrite means for rewriting the detected words into the retrieved representative words;

coding means for coding the text file after the detected words are rewritten by said representative word rewrite means;

take-out means for taking out sentences separately from the text file;

structure-parse means for structure-parsing each sentence to generate an equation tree, said equation tree having a tree structure with a plurality of nodes linked one with another;

string-of-characters conversion means for converting the equation tree into strings of characters, a parent-child relation being represented by a predetermined character; and

sentence conversion means for converting each sentence taken out by said take-out means into the strings of characters, and

wherein said correspondence table storage means stores the predetermined character in relation with strings of bits,

whereby said converting means converts the predetermined character into a string of bits.

38. The text file compressing apparatus of claim 37, wherein said string-of-characters conversion means includes:

a string-of-characters buffer in which the equation tree in the form of strings of characters are arranged;

first placement means for placing a word corresponding to a parent node at a top of the equation tree, and the words corresponding to all children nodes within said string-of-character buffer, all the children nodes being marked by the predetermined character;

current node set means for making each child node a current node in turn;

second placement means for placing a word corresponding to the current node and the words corresponding to all children nodes, all the children nodes being marked by the predetermined character; and

repetition means for repeatedly activating said second placement means for each child node.

39. A method for compressing a text file for a text file compressing apparatus, the apparatus including a text file storage unit for storing text files, a representative word storage unit for classifying a plurality of words into a plurality of sets of synonymous words to store the sets with a representative word for each set, and a code information storage unit for storing code information used to code words in the text file, said method comprising the steps of:

detecting words in sentences comprising the text file;

retrieving the representative words from the sets for the detected words;

rewriting the detected words with the retrieved representative words;

coding the text file after the detected words are rewritten into the representative words while referring to the code information in said code information storage unit;

taking out sentences separately from the text file;

structure-parsing each sentence and generating an equation tree, said equation tree having a tree structure with a plurality of nodes linked one with another;

converting the equation tree into strings of characters, a parent-child relation being represented by a predetermined character; and

converting each sentence taken out by said sentence taking out step into the strings of characters,

wherein said code information storage unit stores the predetermined character in relation with strings of bits,

whereby the predetermined character is converted into a string of bits in said sentence-to-string-of-characters converting step.

40. The method of claim 39, wherein said equation-tree-to-string-of-characters converting step further comprises the steps of:

arranging the equation tree in the form of strings of characters;

placing a word corresponding to a parent node at a top of the equation tree, and the words corresponding to all children nodes arranged in said arranging sub-step, all the children nodes being marked by the predetermined character;

making each child node into a current node in turn;

placing a word corresponding to the current node and words corresponding to all children nodes, all the children nodes being marked by the predetermined character and

repeating said secondly mentioned placing sub-step for each child node.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an apparatus and method for compressing electronic texts to reduce the data size thereof.

(2) Description of the Related Art

The introduction of electronic texts has advanced a so-called "paperless system" in both the civil and public sectors. The electronic texts, or otherwise known as text files, are the texts represented by an array of character codes. The electronic texts are advantageous in that they are easily copied or delivered, and occupy only a small storage area.

When an electronic text is transmitted to a distant correspondent via a communication network, or delivered by means of a recording medium, such as a floppy disk or CD-ROM, the data size of the electronic text is reduced by compressing the character codes to save the communication cost and increase the number of the texts to be stored on one disk.

The electronic texts are generally compressed by lossless coding methods, such as LZW coding and Huffman coding. In the following, Huffman coding will be explained as an example.

In Huffman coding, the probabilities with which words appear in the texts are first determined. Next, bit strings are assigned to the words and an example of the bit strings is shown in FIG. 1: the words assigned short strings of bits have larger probabilities, whereas the words with smaller probabilities map to longer strings of bits. The words in the electronic text are converted into the strings of bits while referring to the compression table shown in FIG. 1. Assume that a sentence "XXX Electric will release a new product." consisting of six words, "XXX Electric", "will", "release", "a", "new", and "product", is converted into a string of bits. If a character code is 8 bits long, then, for example, a 32 bits long (8.times.4=32) word "will" is converted into a 4-bit string "1000" in Huffman coding, reducing the code size to one eighths (4/32=1/8).

Huffman coding is most effective when the probabilities are determined as accurately as possible and the short strings of bits are assigned to the words with large probabilities.

However, in practice, a writer avoids repeating words or phrases and instead uses synonyms to have a wide vocabulary; for example, the writer may use "an apology" for the first occurrence and "an excuse" for the second. This reduces the probabilities for each word, and the resulting Huffman coding is not satisfactorily efficient. In addition, the fact that verbs and auxiliary verbs have different forms makes it difficult to increase compression efficiency. For example, an irregular verb "be" has six forms: "be", "is", "are", "was", "were", and "been". If the verb "be" invariably appears as "is", then the word is compressed efficiently; however, having the different forms reduces the probabilities for the verb "be", and hence making Huffman coding less effective.

There are other coding methods known as "lossy coding". An example of the lossy coding is disclosed in Japanese Laid-open Patent Application No. 4-156663. In the lossy coding, each sentence in one electronic text is morpheme-parsed while referring to a certain dictionary to be partitioned into words. Then, semantic information of each word is retrieved from the dictionary, based on which the importance of each word is determined. If the determined importance is below a predetermined level, such words are deleted to reduce the amount of data. However, because the reduction is limited to the data amount of the deleted words, the compression efficiency is not satisfactory either. Besides, the restored data as a result of compression and subsequent expansion are not true to the original data because some words are omitted.

Huffman coding may be combined with the lossy coding to enhance the compression efficiency: a text is coded after less important words are deleted. However, the text is restored by omitting some words as is with the case in the lossy coding alone.

SUMMARY OF THE INVENTION

Accordingly, the present invention has a first object to provide an apparatus and method for compressing texts efficiently by rewriting synonymous words with a representative word first and then applying a lossless coding method.

The present invention has a second object to provide an apparatus and method for compressing texts efficiently by rewriting words in different forms with their respective infinitives first and then applying a lossless coding method.

The first object can be fulfilled by a text file compressing apparatus comprising: a word detecting unit for detecting words in sentences composing a text file; a representative word storage unit for classifying a plurality of words into a plurality of sets of synonymous words to store the sets with a representative word for each set; a representative word retrieval unit for retrieving the representative words for the detected words from their respective sets in the representative word storage unit; a representative word rewrite unit for rewriting the detected words into the retrieved representative words; and a coding unit for coding the text file after the detected words are rewritten by the representative word rewrite unit.

The coding unit may include: a correspondence table storage unit for storing a correspondence table showing a relation between a plurality of words and string of bits; and a string-of-bits conversion unit for converting each detected word in the text file into the string of bits after the detected words are rewritten into the representative words by the representative word rewrite unit.

The strings of bits in the correspondence table may be variable; and the representative word in each set may be assigned a shortest string of bits compared with other words in the set.

Words with high probabilities with which the words appear in the texts may be assigned short strings of bits, and words with small probabilities may be assigned long strings of bits.

The first object can be also fulfilled by a method for compressing a text file for a text file compressing apparatus including a text file storage unit for storing text files, a representative word storage unit for classifying a plurality of words into a plurality of sets of synonymous words to store the sets with a representative word for each set, and a code information storage unit for storing code information used to code words in the text file, the method comprising the steps of: detecting words in sentences comprising the text file; retrieving the representative words from the sets for the detected words; rewriting the detected words with the retrieved representative words; and coding the text file after the detected words are rewritten into the representative words while referring to the code information in the code information storage unit.

The coding step may include: converting the words in the text file into string of bits after the detected words are rewritten into the representative words, while referring to the code information in the code information storage unit, the code information being stored in the form of a correspondence table showing a relation between a plurality of words and strings of bits.

The coding step may include: converting the words in the text file into string of bits after the words are rewritten into the representative words while referring to the code information, the code information being stored in the code information storage unit in the form of a dictionary including words arranged in an order of probabilities with which the words appear in the file text, the strings of bits showing an order of each word in the code information.

According to the present invention, the synonymous words are rewritten into an adequate representative word first and subsequently compressed based on the probabilities with which the representative word appears in one text. Thus, if a text includes a wide vocabulary, not only is the text compressed efficiently, but also the resorted text is substantially true to the original.

The second object can be fulfilled by a text file compressing apparatus for compressing a text file, the text file compressing apparatus comprising: a detecting unit for detecting words in sentences composing a text file; a form storage unit for storing form information for a plurality of words, the form information composing infinitives and form marks indicating forms of the words; a form information retrieval unit for retrieving the form information that matches with the words detected by the detection unit from the form storage unit; a form information rewrite unit for rewriting the words detected by the detection unit into their respective form information; and a coding unit for coding the text file after the words detected by the detecting unit are rewritten into the representative words by the form information rewrite unit.

The coding unit may include: a correspondence table storage unit for storing a correspondence table showing a relation between a plurality of words and string of bits; and a string-of-bits conversion unit for converting each detected word in the text file into the string of bits after the detected words are rewritten into the representative words by the representative word rewrite unit.

The infinitives may be assigned shorter strings of bits compared with their different forms in the correspondence table.

Words with high probabilities with which the words appear in the texts may be assigned short strings of bits, and words with small probabilities may be assigned long strings of bits.

The correspondence storage unit may further store the form marks in relation with the strings of bits,

whereby the string-of-bits conversion unit converts the form marks into the strings of bits.

The second object can be also fulfilled by a method for compressing a text file for a text file compressing apparatus including a text file storage unit for storing text files, a form storage unit for storing a plurality of words in the form of infinitives and form marks specifying a form of each word, and a code information storage unit for storing code information used to code words in the text file, the method comprising the steps of: detecting words in sentences composing the text file; retrieving form information that matches with the detected words from the form storage unit; rewriting the detected words with their respective form information; and coding the text file after the words are rewritten into the form information while referring to the code information in the code information storage unit.

The coding step may include: converting the words in the text file into string of bits after the detected words are rewritten into the representative words while referring to the code information in the code information storage unit, the code information being stored in the form of a correspondence table showing a relation between a plurality of words and strings of bits.

The rewriting step may include: rewriting the form marks in the text file into strings of bits while referring to the correspondence table, the correspondence table further showing a relation between the strings of bits and form marks.

According to the above structure, the words in different forms are rewritten into their respective infinitives before they are compressed to increase the probabilities. Thus, the compression efficiency can be enhanced.

BRIEF DESCRIPTION OF THE DRAWING

These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention. In the drawings:

FIG. 1 is a view showing a compression table used in Huffman coding;

FIG. 2 is a view depicting a structure of a text compressing apparatus in accordance with a first embodiment of the present invention;

FIG. 3 is a view showing a content of a parse dictionary;

FIGS. 4A through 4C are views showing sentence-to-equation-tree transition;

FIG. 5 is a view showing a content of an expression conversion dictionary;

FIG. 6 is a view showing an equation tree after the rewriting of a word with a representative expression;

FIG. 7 is a view showing another compression table;

FIG. 8 is a flowchart detailing the operation of the text compressing apparatus in the first embodiment;

FIG. 9 is a flowchart detailing the operation of an equation tree converting unit in accordance with a second embodiment of the present invention; and

FIGS. 10A through 10F are views showing a transition from the equation tree to a string of characters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIRST EMBODIMENT

FIG. 2 is a view depicting the structure of a text compressing apparatus in accordance with the first embodiment of the present invention. The text compressing apparatus is installed in a text generating apparatus to reduce the memory size of electronic texts stored in an external storage unit. In this embodiment, assume that the electronic texts are written in English.

The text compressing apparatus comprises a job buffer 10, a control unit 11, a parse dictionary 12, a morpheme-parsing unit 14, a dictionary retrieving unit 15, a structure-parsing unit 16, an expression rewrite dictionary 17, an expression rewriting unit 18, an equation tree converting unit 19, a compression table 20, and a Huffman coding unit 21.

More precisely, the job buffer 10 is a text buffer with a capacity for storing character codes of one electronic text.

The control unit 11 opens a file for a desired electronic text stored in an external storage unit (not shown), and takes out all the sentences separately therefrom to deliver the same to the morpheme-parsing unit 14. Subsequently, the control unit 11 activates the morpheme-parsing unit 14, dictionary retrieving unit 15, structure-parsing unit 16, expression rewriting unit 18, equation tree converting unit 19, and Huffman coding unit 21 in turn.

The parse dictionary 12 stores words referred to as vocabulary indexes in relation with their parts of speech, form marks, and parse patterns as shown in FIG. 3. The form marks identify infinitives of the vocabulary indexes if they are in different forms. The form marks consist of infinitives appended with marks "ORIG", "PRES", "PAST", or "PP" specifying the infinitive, present tense, past tense, and past participle, respectively. The parse pattern is the information indicating which elements of sentence vocabulary indexes are; the elements of a sentence includes a subject, a predicate, an object, a complement, etc.

In the drawing, a form mark "publish. PRES" indicates a vocabulary index to its left is a present tense of a verb "publish", and a parsing pattern "SVO" in its right means that the vocabulary index is placed between a subject and a predicate. Similarly, a form mark "buy.PAST" indicates a vocabulary index to its left is the past tense of a verb "buy", i.e., "bought"; a form mark "be.ORIG" indicates a vocabulary index in to left is