Abstract:
Methods for converting a source character string to a target character string are described herein. In one aspect of the invention, an exemplary method includes receiving a first character string having the source character string, dividing the first character string into a plurality of sub-strings, converting the plurality of the sub-strings to second character strings through a dictionary, creating third character strings corresponding to the plurality of the sub-strings, analyzing the second and third character strings, constructing fourth character strings from the second and third character strings based on the analysis, creating a candidate list based on the fourth character strings, selecting the target character string from the candidate list and outputting the target character string. Other methods and apparatuses are also described.

Description:
[0001]     This application is a continuation of co-pending U.S. patent application Ser. No. 09/965,333. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to the field of electronic text entry, and more particularly to a method of entering Japanese hiragana characters and translating into appropriate Japanese words using a combination of hiragana, katakana and kanji characters.  
       BACKGROUND OF THE INVENTION  
       [0003]     The Japanese written language contains three separate character strings. Simple Japanese characters representing phonetic syllables are represented by the hiragana and katakana character sets (together referred to as “kana”). Hiragana characters, which are characterized by a cursive style, are typically used for words native to Japan. Katakana characters, which are characterized by a more angular style, are typically used for words borrowed from other cultures, or for emphasis and sound effects. The third character set in Japanese is kanji. Kanji are the complex Japanese characters borrowed from the Chinese language. There are over 9000 kanji characters in the Japanese language. Approximately 4000 kanji are used on a semi-regular basis, while knowledge of 2000 kanji is generally required to read a newspaper or get around in Japan. The complexity of the Japanese written language poses several challenges for efficient text entry in computers, word processors, and other electronic devices.  
         [0004]      FIG. 1A  shows an example of Japanese hiragana and katakana characters. The hiragana  151  and katakana  152  character sets each contain 46 base characters. Both sets of kana have identical pronunciations and rules of construction, only the shapes of the characters are different to emphasize the different usage of the words. Some base kana characters are used in certain combinations and in conjunction with special symbols (called “nigori” and “maru”) to produce voiced and aspirated variations of the basic syllables, thus resulting in a full character set for representing the approximately 120 different Japanese phonetic sounds. If a Japanese keyboard included separate keys for all of the voiced and aspirated variants of the basic syllables, the keyboard would need to contain at least 80 character keys. Such a large number of keys create a crowded keyboard with keys, which are often not easily discernible. If the nigori and maru symbol keys are included separately, the number of character keys can be reduced to 57 keys. However, to generate voiced or aspirated versions of a base character requires the user to enter two or more keystrokes for a single character.  
         [0005]     Common methods of Japanese text entry for computers and like devices typically require the use of a standard Japanese character keyboard or a roman character keyboard, which has been adapted for Japanese use. A typical kana keyboard has keys which represent typically only one kana set (usually hiragana) which may be input directly from the keyboard. A conventional method is to take the hiragana text from the keyboard containing the hiragana keys as an input, and convert it into a Japanese text using a process called Kana-Kanji conversion. A typical Japanese text is represented by hiragana, katakana and kanji characters, such as sentence  150 , which has English meaning of “Watch a movie in San Jose”. The text  150  includes katakana characters  154  which are corresponding to a foreign word of “San Jose”, a hiragana character  155  that is normally used as a particle, and a kanji character set  153 .  
         [0006]      FIG. 1B  shows a conventional method of converting a hiragana text to a Japanese text. Referring to  FIG. 1 , the Japanese hiragana characters are entered  101  through a keyboard. The hiragana characters are converted  102  to Japanese texts by looking up characters in a database (e.g., dictionary). Then the user has to inspect  103  and check  104  whether the conversion is correct. If the conversion is incorrect (e.g., the dictionary does not contain such conversion), the user has to manually force the system to convert the hiragana text. A typical user interaction involves selecting  105  portions of the hiragana texts, which are converted incorrectly and explicitly instructing  106  the system to convert such portion. The system then presents  107  a candidate list including all possible choices. The user normally checks  109  whether the conversion is correct. If the conversion is correct, the user then selects  108  a choice as its best output and inserts the correct result to form the final output text. If the conversion is incorrect, the user reselects a different portion of the input and tries to manually convert the reselected portion again.  
         [0007]     One of the conventional methods, transliteration (direct conversion from hiragana to katakana) normally does not provide a correct result for most of the cases, because typically users choose (e.g., in a method shown in  FIG. 1B ), instead of the katakana word, a segment containing the word and one or more trailing post particles that are written in hiragana in the final form. The normal transliteration will also convert all trailing post particles to katakana form which is incorrect.  
         [0008]     Another conventional method generates alternative candidates by transliterating the leading sub-string of the string. This method takes advantage of the fact that the trailing particles are always trailing and are all in hiragana. This method creates many candidates that may include the correct one among them. Following is an illustration of an example of the a conventional method (in English):  
                                                       input:   inthehouse           output 1:   INTHEHOUSE           output 2:   i NTHEHOUSE           output 3:   in THEHOUSE           output 4:   int HEHOUSE           output 5:   inth EHOUSE           output 6:   inthe HOUSE - (correct one)           output 7:   intheh OUSE           output 8:   intheho USE           output 9:   inthehou SE           output 10:   inthehous E           output 11:   inthehouse                      
 
 As described above, the conventional method generates many candidates after the user selects a potion of the input text to be corrected, which may lead to confusion of the final selection, even though such candidates may include a correct choice. Another conventional method involves an analyzer, which can recognize post particles. It analyzes the range from the end until the analyzer cannot find post particles any more. However, the conventional methods require a user to interact thereby potentially lower efficiency in order to achieve accurate results. 
 
         [0009]     One of the disadvantages of the conventional method is that if a Katakana word is not in the dictionary, the conversion containing the Katakana word usually fails. Another disadvantage of this method is that it involves user-specific interaction to convert and select the best candidate. It consumes more time and efforts if the user does not know the possible outputs of the conversion. Hence, a better method to automatically and efficiently convert Japanese hiragana character string to katakana character string is highly desirable.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention discloses methods and apparatuses for converting a first character string to a second character string. In addition to a regular dictionary, the invention includes a virtual dictionary to generate an artificial character string based on the first character string. When the first character string cannot be converted through a regular dictionary (e.g., the regular dictionary does not know the first character string), the invention uses the artificial character string generated by the virtual dictionary to convert the first character string. Therefore, with the virtual dictionary of the invention, the conversion never fails.  
         [0011]     In one aspect of the invention, an exemplary method includes receiving a hiragana input, automatically determining a plurality of possible katakana candidates based on the hiragana input, analyzing the plurality of possible katakana candidates to convert the hiragana input to katakana characters, selecting one of the katakana candidates, and outputting converted text comprising the one of the katakana candidates and, at least in some cases, kanji characters.  
         [0012]     In another aspect of the invention, an exemplary method includes receiving a first character string having the source character string, dividing the first character string into a plurality of sub-strings, converting the plurality of the sub-strings to second character strings through a dictionary, creating third character strings corresponding to the plurality of the sub-strings, analyzing the second and third character strings, constructing fourth character strings from the second and third character strings based on the analysis, creating a candidate list based on the fourth character strings, selecting the target character string from the candidate list and outputting the target character string.  
         [0013]     In one particular exemplary embodiment, the method includes constructing the fourth character strings from the second character strings, if the second character strings contain a character string corresponding to the first character string, and constructing the fourth character strings from the third character strings if the second character strings do not contain the character string corresponding to the first character sting. In another embodiment, the method includes examining the output of the conversion to determine whether the conversion is correct, providing the candidate list of alternative character strings if the conversion is incorrect, and selecting a character string from the candidate list as a final output. In a further embodiment, the method includes providing an artificial target character string and updating the database based on the artificially created character string.  
         [0014]     The present invention includes apparatuses which perform these methods, and machine readable media which when executed on a data processing system, causes the system to perform these methods. Other features of the present invention will be apparent from the accompanying drawings and from the detailed description which follows.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements.  
         [0016]      FIG. 1A  shows examples of Japanese characters including hiragana, katakana, and kanji characters.  
         [0017]      FIG. 1B  shows a conventional method of converting a hiragana text to a Japanese text.  
         [0018]      FIG. 2  shows a computer system which may be used with the present invention.  
         [0019]      FIG. 3  shows one embodiment of the kana-kanji conversion system of the present invention.  
         [0020]      FIG. 4  shows an example of calculation of cost values of the katakana character set used by one embodiment of the invention.  
         [0021]      FIG. 5  shows another embodiment of the kana-kanji conversion system with user interaction of the present invention.  
         [0022]      FIG. 6A  shows an embodiment of conversion processes from hiragana character set to katakana character set of the invention.  
         [0023]      FIG. 6B  shows an illustration of an example of the invention versus a process of a conventional method.  
         [0024]      FIG. 7  shows a method of converting hiragana characters to katakana characters of the invention.  
         [0025]      FIG. 8  shows another embodiment of conversion processes from hiragana character set to katakana character set of the invention.  
         [0026]      FIGS. 9A and 9B  show another method of converting hiragana characters to katakana characters of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0027]     The following description and drawings are illustrative of the invention and are not to be construed as limiting the invention. Numerous specific details are described to provide a thorough understanding of the present invention. However, in certain instances, well-known or conventional details are not described in order to not unnecessarily obscure the present invention in detail.  
         [0028]     Japanese is written with kanji (characters of Chinese origin) and two sets of phonetic kana symbols, hiragana and katakana. A single kanji character may contain one symbol or several symbols, and may, by itself, represent an entire word or object. Unlike kanji, kana have no intrinsic meaning unless combined with other kana or kanji to form words. Both hiragana and katakana contain 46 symbols each. Combinations and variations of the kana characters provide the basis for all of the phonetic sounds present in the Japanese language. All Japanese text can be written in hiragana or katakana. However, since there is no space between the words in Japanese, it is inconvenient to read a sentence when the words of the sentence are constructed by either hiragana or katakana only. Therefore most of the Japanese texts include hiragana, katakana and kanji characters. Normally, kanji characters are used as nouns, adjectives or verbs, while hiragana and katakana are used for particles (e.g., “of”, “at”, etc.).  
         [0029]     As computerized word processors have been greatly improved, the Japanese word processing can be implemented through a word processing software. Typical Japanese characters are inputted as hiragana only because it is impractical to include all of hiragana, katakana and kanji characters (kana-kanji) in a keyboard. Therefore, there is a lot of interest to create an improved method of converting hiragana characters to katakana characters. The present invention introduces a unique method to convert hiragana characters to katakana characters automatically based on the predetermined relationships between hiragana characters and katakana characters. The methods are normally performed by software executed in a computer system.  
         [0030]      FIG. 2  shows one example of a typical computer system, which may be used with the present invention. Note that while  FIG. 2  illustrates various components of a computer system, it is not intended to represent any particular architecture or manner of interconnecting the components as such details are not germane to the present invention. It will also be appreciated that network computers and other data processing systems (e.g., a personal digital assistant), which have fewer components or perhaps more components, may also be used with the present invention. The computer system of  FIG. 2  may, for example, be an Apple Macintosh computer or a personal digital assistant (PDA).  
         [0031]     As shown in  FIG. 2 , the computer system  200 , which is a form of a data processing system, includes a bus  202  which is coupled to a microprocessor  203  and a ROM  207  and volatile RAM  205  and a non-volatile memory  206 . The microprocessor  203 , which may be a G3 or G4 microprocessor from Motorola, Inc. or IBM is coupled to cache memory  204  as shown in the example of  FIG. 2 . The bus  202  interconnects these various components together and also interconnects these components  203 ,  207 ,  205 , and  206  to a display controller and display device  208  and to peripheral devices such as input/output (I/O) devices which may be mice, keyboards, modems, network interfaces, printers and other devices which are well known in the art. Typically, the input/output devices  210  are coupled to the system through input/output controllers  209 . The volatile RAM  205  is typically implemented as dynamic RAM (DRAM) which requires power continually in order to refresh or maintain the data in the memory. The non-volatile memory  206  is typically a magnetic hard drive or a magnetic optical drive or an optical drive or a DVD RAM or other type of memory systems which maintain data even after power is removed from the system. Typically, the non-volatile memory will also be a random access memory although this is not required. While  FIG. 2  shows that the non-volatile memory is a local device coupled directly to the rest of the components in the data processing system, it will be appreciated that the present invention may utilize a non-volatile memory which is remote from the system, such as a network storage device which is coupled to the data processing system through a network interface such as a modem or Ethernet interface. The bus  202  may include one or more buses connected to each other through various bridges, controllers and/or adapters as are well known in the art. In one embodiment the I/O controller  209  includes a USB (Universal Serial Bus) adapter for controlling USB peripherals.  
         [0032]      FIG. 3  shows a system used by an embodiment of the invention. Referring to  FIG. 3 , the system  300  typically includes an input unit  301 , an input method UI, and system interface  302 , a morphological analysis engine (MAE)  303 , a dictionary management module (DMM)  305  and an output unit  308 . The input unit  301  may be a keyboard such as I/O device  210  of  FIG. 2 . The input unit may be a touch pad, such as a personal digital assistant (PDA). The input unit may be a set of application programming interfaces (APIs) that receive inputs from an application. Other types of inputs may exist. The input unit  301  accepts Japanese characters inputted (e.g., Japanese hiragana characters). The hiragana characters are transmitted to the input method and interfaces  302 , which in turn transmits to the MAE  303 . The MAE  303  then accesses to a databases, such as regular dictionaries  307  and virtual dictionary  306 , through DMM  305 . The regular dictionaries  307  may include most known Japanese words corresponding to the hiragana words. The regular dictionaries  307  may be stored in a random access memory (RAM), such as volatile RAM  205 , or it may be stored in a hard disk, such as nonvolatile memory  206 . In one embodiment, the regular dictionaries  307  may be stored in a remote storage location (e.g., network storage), through a network. It is useful to note that the present invention may be implemented in a network computing environment, wherein the regular dictionaries may be stored in a server and an application executed in a client accesses to the regular dictionaries through a network interface over a network. Multiple applications executed at multiple clients may access the regular dictionaries simultaneously and share the information of the regular dictionaries over the network. Although the regular dictionaries  307  are illustrated as single dictionary, it would be appreciated that the regular dictionaries  307  may comprise multiple dictionaries or databases. In another embodiment, the regular dictionaries  307  may comprise multiple look-up tables. The virtual dictionary  306  may direct convert every single hiragana character to a katakana character. The virtual dictionary may contain a look-up table to look up every single katakana character for each hiragana character. The DMM  305  is responsible for managing all dictionaries including dictionaries  306  and  307 . DMM  305  is also responsible for updating any information to the dictionaries upon requests from the MAE  303 . In one embodiment, the DMM  305  also manages another database  304  where all of the rules or policies are stored.  
         [0033]     The virtual dictionary  306  may include direct translation of the hiragana characters to katakana characters. The virtual dictionary  306  may return all multiple words with different part of speeches. In one embodiment, the virtual dictionary may return three parts of speeches. They are noun, noun that can be used as verb and adjective. It is useful to note that artificially generated katakana words from the virtual dictionary look no different from regular words once they are returned from the virtual dictionary.  
         [0034]     In another embodiment, the dictionary database may be divided into two or more dictionaries. One of them is a regular dictionary containing regular words. The other dictionary is a special dictionary (e.g., so-called virtual dictionary). The special dictionary may contain all possible katakana characters including the artificial katakana characters created during the processing. The katakana is straight transliteration of the hiragana input. The virtual dictionary may return multiple words with different part of speeches. Each word has its priority value. Such priority value may be assigned by the virtual dictionary. For example, in the implementation for string “A-Ka-Ma-I”, the dictionary may return three outputs with different part of speeches, Noun, Noun that is associated with verb and adjective, as follows:  
         [0035]     A-Ka-Ma-I POS: Noun Priority: 100  
         [0036]     A-Ka-Ma-I POS: Noun that can work as a verb Priority: 100  
         [0037]     A-Ka-Ma-I POS: Adjective Priority: 100  
         [0000]     Other implementations may exist.  
         [0038]     Three words can be considered as one record, or they may be considered as three separate records. The priority value can be the same for all words returned from the dictionary. The priority value could be calculated from the katakana and/or the part of speeches. In one embodiment, the priority value is determined by the length of the word. In another embodiment, the priority may be based on bi-gram and tri-gram statistics of the katakana and can be adjusted based on the part of speeches. Typically the priority value is set lower than all or most of regular words in regular dictionaries, in order to prevent the artificial katakana words from appearing as the most probable conversion when there are proper regular words available.  
         [0039]     Part of speeches defines how often or easy words of a certain part-of-speech come next to the other words of certain part-of-speech. It could be just yes/no value. Subject to the implementation, there are cases one word has two part-of-speeches. One for the right side connection and the other for left side connection. Also, there are cases that it is also used to determine not only the next or previous words, but also the connection with words at before the previous or after the next.  
         [0040]     Referring to  FIG. 3 , the MAE  303  sends a request to DMM  305  to convert the inputted hiragana words. The DMM  305  searches the regular dictionaries  307  for corresponding Japanese words. At the mean while, the MAE  303  then sends a request to DMM  303  to retrieve all possible katakana character combinations from the virtual dictionary  306 . In general the MAE  303  will select the words from the regular dictionaries  307 , if the dictionaries  307  contain such direct translation. Otherwise, the MAE  303  will select an artificial katakana word created by the virtual dictionary  306 .  
         [0041]     The MAE  303  also invokes a set of rules from a database  304  and applies the set of rules to the analysis of all possible combinations. The database  304  containing the rules may be a separate database, or it may be the same database as the dictionary  306  or  307 . Each of the possible combinations is associated with a usage frequency. The usage frequency represents how frequent the characters are previously being used. The dictionary may also include a connection relationship between each character set (e.g., noun, adjective, and verb, etc.). The set of rules may include the information of usage frequency and connection relationship. The MAE  303  applies these rules to construct a possible candidate pool or list from the possible combination from the dictionary  306 , based on the set of rule. In one embodiment, the set of rules may include semantic or grammar rules to construct the candidate list. For example, the word “hot” may mean hot temperature or mean spicy food. When the word “hot” is associated with the word “summer”, e.g., “hot summer”, the word “hot” means more like “hot temperature”, rather then “spicy”. The MAE  303  may calculate the cost values of the candidates based on the set of rule. The final candidate may consist of the least cost value among the candidate list.  
         [0042]      FIG. 4  shows an example of two candidates being constructed to represent the word of “San Jose”, where each of them comprises a usage frequency. The first choice comprises character  401 ,  402  and second choice comprises character set  404 . Character  404  is a particle. Character  401  has a usage frequency of f 1  and character  402  has a usage frequency f 2 . The particle character  403  has a usage frequency f 3 . In addition, the connection between characters  401  and  402  is c 1  and c 2  between characters  402  and  403 . As a result, the cost value of the first choice may be:  
         [0043]     Cost Value 1=f 1 +f 2 +f 3 +c 1 +c 2   
         [0000]     Similarly, the second choice may have cost value of:  
         [0044]     Cost Value 2=fa+f 3 +ca  
         [0045]     In one embodiment, the cost values may include semantic or grammar factors. The evaluation unit  303  evaluates the cost values of two choices and selects the one with the least cost value, in this case cost value 2, as a final output of the conversion.  
         [0046]     However, although the evaluation unit selects the final output based on least cost value and in most cases the selected outputs are correct, in some rare cases, the correct output may not has least cost value. Under the circumstances, the invention provides an opportunity for a user to interact.  FIG. 5  shows another embodiment of the present invention. Referring to  FIG. 5 , the system  300  provides a user interaction  309 , where the user can examine the output generated by the MAE  303  and determine whether the output is correct. If the user decides the output is incorrect, the MAE  303  retrieves the candidate list from the database (e.g., virtual dictionary  306 ), through DMM  305 , and displays the candidate list to a user interface. In one embodiment, the user interface may be a pop-up window. The user then can select the best choice (e.g., final choice) from the candidate list as an output. In a further embodiment, the output may be transmitted to an application through an application programming interface (API), from which the application may select a final choice.  
         [0047]     In another embodiment, if the candidate list does not contain a correct output the user desires, the invention further provides means for user directly enters the final output manually and force the system to convert the hiragana characters to katakana characters. The system will update its database (e.g., virtual dictionary  306  or regular dictionaries  307 ) to include the final output katakana word entered by the user as a future reference. In a further embodiment, the user may in fact modify the rules applied to the conversion and store the user specific rules in the database  304 .  
         [0048]      FIG. 6A  shows a block diagram of an embodiment of the invention. A Japanese hiragana character string  601 , which has English meaning of “Watch a movie in San Jose”, is inputted to the system. The morphological analysis engine (MAE)  604  will look up a database, such as dictionaries  307 , to search corresponding Japanese words. The system transmits the portion  602  to the morphological analysis engine (MAE)  604 , through a user interface  616 . The MAE  604  divides the input into a plurality of sub-strings and communicates with the dictionary management module (DMM)  608  and looks up dictionaries  606  for direct translation for each sub-string. At the mean while, the DMM instructs the virtual dictionary  607  to create all possible katakana words corresponding to each sub-string. As a result, a pool of words  605  is formed with regular Japanese words from the regular dictionaries  606  and artificially created katakana words from the virtual dictionary  609 . In one embodiment, each of those Japanese character strings  605  is associated with a usage frequency value and there is connection relationship information between each of the character set. In another embodiment, each of the character strings  605  is associated with a priority value. Typically the priorities of the artificially created katakana words are lower than the regular words from the regular dictionaries to prevent any confusion. That is, the system will pick the regular words from the regular dictionaries over the artificially created katakana words. The system utilizes the artificially created words only when there are no corresponding regular words from dictionaries  606 . The priority information may be stored in the dictionaries  606  as well. Next, the MAE  604  evaluates and analyzes the character strings  605  and applies a set of rules from the database  607 . Although database  607  and dictionary  606  are illustrated as separate databases, it would be appreciated that these two databases may be combined to form a single database. The MAE  604  constructs another set of character strings  610  from the character strings  605 , based on the set of rules. The words  610  are considered as a candidate list, where the word with least cost value is considered higher priority, such as word  611 , while the character set with high cost value, such as word  612 , is considered lower priority. Other priority schemes may exist. Based on the candidate list, the MAE  604  selects a candidate with higher priority, such as character strings  613  as final target character string. The character string  613  is then applied to the rest of the character strings to form the final sentence  614 .  
         [0049]      FIG. 6B  shows a method used by the invention against a conventional method. Referring to  FIG. 6B , a Japanese hiragana character string  651 , which has an English meaning of “San Jose”, is inputted through an input method. The input method normally divides the input into multiple sub-strings  652 . For each of the multiple sub-strings, the dictionaries  653  are used to convert the sub-strings  652  as much as possible into another set of Japanese words  654 . The dictionaries  653  normally contain most of the known words, such as word  663 . However, in the case of word “San Jose”, such as word  662 , it is not known to the dictionaries. Thus, the dictionaries are not able to convert it, leaving the word  662  unavailable. A conventional method will perform analysis on the words  654 , applies rules  664  (e.g., grammar rules), and generates a candidate list  660 . From which word  661  is selected as a final candidate, which is incorrect. As a result, a user must manually convert the input  651  to generate the correct conversion.  
         [0050]     The present invention introduces a virtual katakana dictionary  655 . In addition to the conversion using regular dictionaries, the virtual dictionary  655  takes the sub-strings  652  and creates a set of corresponding artificial katakana words  656 . By combining the regular words  654  from the dictionaries  653  and the artificial katakana words  656  generated from the virtual dictionary  655  and applying set of rules, the full set of words  658  corresponding to the sub-strings are created. As a result, each of the sub-strings has its corresponding converted string, which may be a regular Japanese word, such as word  663 , or an artificial katakana word. The invention then creates a candidate list  658  based on the set of rules  657 . Each of the candidates is associated with a priority based on the rules. From the candidate list the word with highest priority is selected as final correct candidate  659 .  
         [0051]      FIG. 7  shows a method of an embodiment of the invention. Referring to  FIGS. 6A and 7 , the method starts with inputting  701  Japanese hiragana characters, such as hiragana character string  601 . It divides  702  the hiragana character string into multiple sub-strings and converts  708  each of the sub-strings into Japanese words through a dictionary, such as dictionaries  606 . At the mean while, the method creates  703  all possible katakana character strings related to the input, through the virtual dictionary  609 . A pool of the Japanese words  605  is formed from both the regular words and artificial katakana words. It then constructs  704  a candidate list  610 , wherein the candidate with lower cost value has higher priority while the candidate with higher cost value has lower priority. The priority of the artificially created katakana words may be assigned by the virtual dictionary. The method then analyzes  705  the candidate list and selects  707  the best candidate  613  (e.g., lowest cost value) based on the analysis. The final candidate is then outputted  708  to form the final sentence  614 .  
         [0052]      FIG. 8  shows another embodiment of the invention, where the invention may involve a user interaction. The input  601  contains Japanese hiragana character string where portion  602  (e.g., “San Jose”) cannot be directly converted, while portion  603  can be converted through regular dictionaries  606 . The system then uses virtual dictionary  609  to create all possible corresponding katakana words for every single sub-strings of portion  602 . The morphological analysis engine (MAE)  604  then constructs a candidate list  610  based on a set of rules. The set of rules may include character&#39;s usage frequency and connection relationship information between the characters. In another embodiment, the set of rules may contain semantic and grammar rules. A cost value is calculated for each candidate of the list. The candidate with the least cost value has highest priority, while the candidate with the most cost value has lower priority. As shown in  FIG. 8 , candidate  611  has highest priority among the candidates in the list. As a result, candidate  611  is selected as a final choice for the conversion by the evaluation unit  609 . However, in some rare cases, the choice  611  may not be correct, in which case, it involves a user interaction  615 . During the user interaction, the user selects portion of the input, such as portion  602  which has an English meaning of “San Jose” and instructs the system to convert it. The system will pull out the pool of all candidates, such as candidate list  610 . In one embodiment, the candidate list is displayed through user interface, such as a pop-up window. From the list, the user selects the final output  616  and forms the final sentence  614 . Based on the user&#39;s selection, the system may update its database (e.g., dictionaries  606  and virtual dictionary  609 ), so that subsequent conversion will most likely succeed.  
         [0053]      FIG. 9  shows a method of another embodiment of the invention, converting a source character string to a target character string. The method receives a first character string having the source character string from a user interface. It divides the first character string into multiple sub-strings. It then converts the sub-strings to second character strings through a dictionary. At the same time, the method creates third character strings corresponding to the sub-strings through a virtual dictionary. It then analyzes the second and third character strings and constructs fourth character strings based on the analysis. Next it creates a candidate list based on the priority information and selects the final candidate with the highest priority from the candidate list.  
         [0054]     Referring to  FIG. 9 , Japanese hiragana character string is received  901  through a user interface, such as keyboard. In one embodiment, the user interface may include a touch pad from a palm pilot, or other inputting devices. In a further embodiment, the Japanese hiragana character string may be received from an application software through an application programming interface (API). The hiragana character string is divided  902  into multiple sub-strings. The morphological analysis engine (MAE) then communicates with the dictionary management module (DMM) to convert  903  each of the sub-strings into corresponding Japanese words through regular dictionaries. At the same time, the MAE also instructs DMM to create  904  all possible katakana words corresponding to the sub-strings through the virtual dictionary. Next the system constructs  905  possible candidates from the all possible words including Japanese words from the regular dictionaries and artificial katakana words generated from the virtual dictionary, and forms a candidate list. The possible choices of the katakana words from the virtual dictionary may include part speech information. The system may use a set of rules to construct the candidates. In one embodiment, the set if rules may include usage frequency of each katakana character set and connection relationship between each choice. In another embodiment, the set of rules may include word&#39;s semantic or grammar rules. This information may be stored in the database where the all possible katakana character sets are stored. In another embodiment, these rules may be stored in a separate database. The system next retrieves  906  the usage frequency and connection relationships from the database, and applies  907  the semantic and grammar rules to the analysis. Based on this information, the system calculates  908  cost values for all candidates. The candidate with least cost value is then selected  909  as final target character set. The final target character set may be displayed to a user interface in a display device.  
         [0055]     In a yet another aspect of the invention, a user may inspect  910  the result provided by the kana-kanji conversion engine to check  911  whether the conversion is correct. If the user is satisfied with the result, the conversion is done. However, if the conversion is incorrect, the user selects  912  the portion of the input (e.g., original hiragana input) and instruct the system to explicitly convert it. The system in turn provides all possible combination of Japanese words including the artificial katakana words, in a form of candidate list. The user then retrieves  913  such candidate list and display in a user interface. In one embodiment, the user interface is in a form of pop-up window. Next, the user may check  914  whether the candidate list contain the correct conversion. If the candidate list contains the correct conversion, the user selects  915  the best candidate from the candidate list. The system then updates  916  its database (e.g., knowledge bases) of the parameters (e.g., usage frequency, connection relationship, etc.) regarding to the user selection. The final selection is then outputted  917  to the application. In one embodiment, if the candidate list does not contain the correct result, the user may construct  918  and create the correct result manually through a user interface. Once the artificial conversion is created by the user, the system saves  919  such results in its database as a future reference.  
         [0056]     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set fourth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.