Abstract:
A character input device is disclosed. The device includes a character input section including a plurality of character keys; a display section that displays an input character(s); and a next word prediction section that predicts a respective word being subsequently input in an event of input-word reception in the character input section and that displays the word as a next word candidate on the display section. The next word prediction section stores usage history information indicative of whether the next word candidate for the respective input-received word was used by a user, and determines in accordance with the usage history information of words as of a time point of the event of input-word reception of the word whether to display the next word candidate on the display section, and inhibits the display of a next word candidate when a value obtained by adding a constant to the number of used times of the candidate is smaller than the number of its unused times.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present invention contains subject matter related to Japanese Patent Application JP 2007-140207 filed in the Japanese Patent Office on May 28, 2007, the entire contents of which being incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a character input device, a mobile terminal, and a character input program for execution of character input on a display screen by use of two or more keys. 
     2. Description of the Related Art 
     In a device, such as a mobile phone terminal, in which the number of keys usable for character input is small, generally two or more characters are allocated to one key. In this case, each time the same key is serially pressed (or, the keystroke of the same key is serially entered), a different character is presented serially or one by one as an input candidate on a display screen of the terminal on the basis of selection from among the characters allocated to the key. As such, depending upon the character, the keystroke of the key has to be repeatedly entered to input a character of interest (or, a “target character,” herebelow). In other words, in order to input a single word, a user has to enter a large number of keystrokes relative to the number of characters composing the word. This is a complicated, time-consuming operation for the user. 
     Various approaches as solutions have been proposed to date against problems such as described above, and some of the solutions are practically used as practical applications. 
     One of such practical applications is known as a technique called “predicative conversion.” The technique, in the event that either a character under input operation or a character string is entered or input, presents selective items corresponding to the target word predicted in accordance with past input historical log information or context on a display screen to thereby allow a user to make selection. As one of such predicative conversion techniques, “POBox” (Predictive Operation Based On example) is known (“POBox” is a registered trademark of Sony Corporation). 
     As one of other input techniques, a so-called single-tap technique is known. According to this technique, by serially entering keystrokes of keys to each of which a target character is allocated, a word associated to the keystrokes of the keys and stored in a dictionary is retrieved and presented as a selective item to the user. 
     Also known is a next word prediction technique in which, in a device, past input history information for predicting a next word desired to be input after a certain word has been input are stored. Thereby, when the certain word is input, a word to be input next (“next word,” herebelow) is predicted in accordance with the input history information, and the predicted word is presented as a selective item to a user. 
     SUMMARY OF THE INVENTION 
     The present invention relates to improvement of a next word prediction technique such as described above. However, the existing next word prediction technique is based on input history information of a pair of words successively input by a user in the device, and poses problems as described below. 
     In the event that a next word prediction function is active or in an on state, when a subsequent word to a certain word is stored, the “next word” is predicted and displayed as a selective item on a screen each time the “certain word” is input. However, when the user attempts to input a word different from a word input in the past in succession to the “certain word,” the selective item displayed is annoyance and obstructive. 
     When the next word prediction function is turned off, while the troublesome is cancelled, next word prediction cannot be used at all in such a case. 
     Actually, depending on the case, the next word prediction function is necessary or unnecessary for a user. However, in the case where the next word prediction function is required to be switched on/off by the user each time during character input, the operation of the on/off switching is rather burdensome, such that the operation is not realistic. 
     Under these circumstances, it is intended to provide a technique in which, in an character input device, automatic on/off switching of a next word prediction function is executed in response to a history of operations of a user and the switching is executed to meet an intention of the user as much as possible. 
     According to one embodiment of the present invention, a character input device includes a character input section including a plurality of character keys; a display section that displays an input character(s); and a next word prediction section that predicts a respective word being subsequently input in an event of input-word reception in the character input section and that displays the word as a next word candidate on the display section. The next word prediction section stores usage history information indicative of whether the next word candidate for the respective input-received word was used by a user, and determines in accordance with the usage history information of words as of a time point of the event of input-word reception of the word whether to display the next word candidate on the display section. 
     According to the embodiment, even when the next word prediction section (corresponding to the next word prediction function described above) is used, next word candidates are not displayed at all times in a fixed manner. However, the next word candidates are displayed on the display section in accordance with user&#39;s past usage historical logs of the next word candidates, and are inhibited from being displayed on the display section, for example. By use of such past usage historical logs of the same user, a next word candidate for a word with a high next word candidate use frequency is displayed on the display section, but a word with a low next word candidate use frequency is inhibited from being displayed on the display section. Thereby, the next word candidate usage probability of the user can be determined with a relatively high accuracy. In this manner, when it is determined from a past usage historical log that the user is not likely to use a next word candidate, the next word is inhibited from being displayed on the display section. As a consequence, complexity resulting from all-time automatic display of next word candidates to the user is avoided. On the other hand, when it is determined that the user is likely to use a next word candidate, the next word candidate is automatically presented to the user. 
     Even when display of a next word candidate is inhibited, the next word candidate is displayed in response to the predetermined specification of the user. Thereby, even when the result of prediction in accordance with the past usage historical log does not match exactly with a request, an appropriate countermeasure can be provided. 
     The configuration of the character input device may be such that, when a numeric value of the number of used times of the next word candidate is smaller than a numeric value of the number of unused times of the next word candidate, the next word prediction device inhibits display of the next word candidate. In this case, the degree of displayability of the next word candidate is adjusted. 
     According to another embodiment of the present invention, a mobile terminal includes a character input section including a tenkey section wherein a plurality of characters are allocated to one character key; a display section that displays an input character(s); and a next word prediction section that predicts a respective word being subsequently input in an event of input-word reception in the character input section and that displays the word as a next word candidate on the display section. The next word prediction section stores usage history information indicative of whether the next word candidate for the respective input-received word was used by a user, and determines in accordance with the usage history information of words as of a time point of the event of input-word reception of the word whether to display the next word candidate on the display section. The operation of the mobile terminal is similar to the operation of the character input device described above. 
     According to still another embodiment of the present invention, there is provided a character input program that is executed in a device including a character input section including a plurality of character keys, and a display section that displays an input character(s). The program causes a computer to execute steps including configuring a next word candidate database in a manner that, each time a word is input by the character input section, a next word input in succession to the word is stored in correlation therewith; storing next word candidate history information containing a number of used times of a next word candidate for the input word and a number of unused times of the next word candidate; when the next word candidate database is referenced each time a word is input, and the input word is thereby recognized to be a word stored in the next word candidate database, determining whether to display a next word candidate(s) for the word on the display section in accordance with the next word candidate history information; updating the next word candidate history information in regard to the input word; and displaying the next word candidate(s) on the display section when the next word candidate is determined to be displayed on the display section. 
     According to the embodiments of the present invention, in the character input device, ON/OFF switching of the next word prediction function (next word prediction section) does not have to be carried out by the user in accordance with the user&#39;s operation history. However, according to the embodiments, when the probability of requiring next word prediction is high, the next word candidate display is automatically performed; however, when the probability is not high), the next word candidate display can be inhibited. Consequently, a character input operation excellent in usability for users can be realized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a schematic block diagram showing a general configuration of a character input device of one embodiment of the present invention; 
         FIG. 2  is a view showing an exterior of a mobile phone terminal as one example of the character input device shown in  FIG. 1 ; 
         FIG. 3  is a block diagram showing a general hardware configuration of the mobile terminal shown in  FIG. 2 ; 
         FIG. 4  is a view showing an example of a structure of an input word list of words input by a user as history information in one embodiment of the present invention; 
         FIG. 5  is a view showing an example of the general contents of a next word candidate database in the embodiment of the present invention; 
         FIGS. 6A to 6C , respectively, are views showing examples of setting screens that are used for ON/OFF setting of a next word prediction function in the embodiment of the present invention; 
         FIGS. 7A to 7F , respectively, are views of examples of screen transitions of character input on a mobile terminal in the embodiment of the present invention; 
         FIGS. 8A to 8E , respectively, are views of examples of screen transitions continued from the screen of  FIG. 7F ; 
         FIGS. 9A to 9C , respectively, are examples of screen transitions in the case where a single-tap input technique is employed in the event the user inputs the word “to” on the screen of  FIG. 8D ; and 
         FIG. 10  is a flow diagram of a process that is executed by a data processing section that realizes an example of the operation of the next word prediction function (shown in  FIG. 1 ) in the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described herebelow with reference to the accompanying drawings. 
       FIG. 1  is a schematic block diagram showing a general configuration of a character input device  100  of one embodiment of the present invention. The character input device  100  includes at least a data processing section  101 , a character input section  110 , a storage section  120 , and a display section  130 . 
     The data processing section  101  is a control section as a CPU (central processing unit) that provides control of devices through program control. As major functions in the present embodiment, a document creating section  103 , and a next word prediction section  105  are provided (a “word” hereinbelow will represent a “word or phrase”). 
     The character input section  110  provides an input interface through which a user inputs, for example, instructions and information, into the character input device  100 . The character input section  110  includes at least multiple keys (inclusive of tenkeys) and various control keys. 
     The storage section  120  is a section that stores therein, for example, an OS (operating system) and programs, such as various applications, which are executed by the CPU  101 , and various types of data. The storage section  120  can include storage mediums, such as a ROM (read-only memory), a flash ROM, a RAM (random access memory), and an HDD (hard disk drive). In the present example, the storage section  120  includes, for example, a next word candidate database  121 , next-word candidate usage historical log information  123 , and a document storage section  125 . The storage section  120  can further include a dictionary containing therein words, for example. 
     The display section  130  provides a display interface that presents information to the user by way of a display screen. The display section  130  is inclusive of, for example, an LCD (liquid crystal display) or a display device of an organo-EL (electroluminescence), and a display control circuit therefor. 
     In general, in the present invention, the word refers to one semantic unit composed of one or more (multiple) characters; and more specifically, in the present embodiment, the word corresponds to a word (as such, the “word” will be simply referred to as “word,” herebelow). 
     In input of text, such as English text using characters of the alphabet, a word is written in a segmentation manner. More specifically, a word-to-word portion is segmented with a space. The manner for space insertion is not specifically limited. For example, normally, the portion of one word of a character string of the alphabet is not known to the terminal, such that a space is inserted corresponding to a predetermined operation of the user, such as an operation (pressing a “#” key, for example) of moving, for example, a cursor  73  to the input position of the next word respective phase. Alternatively, however, when a specific operation for confirming one word is carried out, the space can be automatically inserted. For example, when the operation of confirming one word, such as an operation of input of a symbol such as period, comma, colon, or semicolon, or an operation of selection of a word candidate in the event of a word prediction change is carried out, the space may be automatically input after the word. 
       FIG. 2  shows an exterior of a mobile terminal  200  as one example of the character input device  100  of the embodiment of the present invention. In the present example, there is shown the mobile terminal  200 , which is a so-called foldable or flip type mobile terminal, but the present invention is not limited thereby. For example, the terminal type may be any one of, for example, straight-bar and slidable types.  FIG. 2  is a front view of the foldable-type mobile terminal  200  in an open state. 
     The mobile terminal  200  includes a hinge portion  18  and an upper housing  14  and a lower housing  25  that are coupled to be openable or closable around the hinge portion  18 .  FIG. 2A  is a view of the mobile phone in an open state as viewed from an inner surface side (side of surfaces mated with one another in the close state); and  FIG. 2B  is a view of the mobile phone in the open state as viewed from the outer surface side. A speaker  12  is disposed in an upper portion of an inner face of the upper housing  14 , and a display section  16  (corresponding to the display section  130  of  FIG. 1 ) is disposed on an inner major face. 
     On an inner face of the lower housing  25 , a jog dial  20 , which is rotatable pressing switch, is disposed in the center of an upper portion. In addition, left and right keys  26   a  and  26   b  are disposed in two end portions of the jog dial  20 , and soft keys  17   a  and  17   b  are disposed in two side portions of the left and right keys  26   a  and  26   b . A communication key  21 , a clear key  22 , and a power/on-hook key  23  are disposed below the above-described operation keys. Further, below these keys there is disposed tenkey section  28  (corresponding to the character input section  110  of  FIG. 1 ), and below these keys, there are disposed a memo key  30  and a manner key  31  are disposed. A microphone  32  is disposed in the lowest portion of the lower housing  25 . 
     The detail configuration as described above is only an example for description purposes, and the present invention is not limited thereby. For example, in the mobile terminal  200  of the present embodiment, input of characters of the alphabet is primarily performed, so that the mobile terminal  200  may be of a type that support input of alphabet character and does not support input of kana characters (Japanese). 
       FIG. 3  is a block diagram showing a general hardware configuration of the mobile terminal  200  shown in  FIG. 2 . 
     The mobile terminal  200  includes components interconnected via a bus  215 . The components are a control section  201 , a communication section  203 , a display section  204 , an operation section  205 , a memory  206  (storage section), an audio processing section  210 , a speaker  211  connected to the audio processing section  210 , a microphone  212 , and a calender-time measurement section  213 . 
     The control section  201  corresponds to the data processing section  101  of  FIG. 1 , and includes, for example, a CPU to thereby control the respective sections of the mobile terminal  200 . The communication section  203  includes, for example, an RF section and a modulation circuit, thereby to effect wireless or RF communication with a base station via an antenna  202  for telephonic communications, mail data, and Web data, for example. 
     The display section  204  corresponds to the display section  130  of  FIG. 1  and the display portion  16  of  FIG. 2 , as described above. 
     The operation section  205  corresponds to the character input section  110  of  FIG. 1 , and includes the various keys, such as tenkeys, of  FIG. 2 . The operation section  205  receives, for example, instructions and data inputs from the user. 
     The memory  206  (storage section) corresponds to the storage section  120  of  FIG. 1 , and includes, for example, an ROM and a RAM. The memory  206  (storage section) stores therein an OS and programs such as various applications that the CPU executes, and various types of data. The ROM can include a rewritable nonvolatile memory, such as a flash memory. 
     The audio processing section  210  includes, for example, a voice encoder, a voice decoder, a D/A (digital to analog) converter, and an A/D (analog to digital) converter. The audio processing section  210  performs audio output to the speaker  211  (including an earphone) and audio input from the microphone  212 . 
     The calender-time measurement section  213  provides, for example, current date and time information and a calender function in accordance with an RTC (realtime clock). 
     Although not shown, the mobile terminal  200  includes other functional sections, such as a power supply section, light emitting section, and vibrator, similarly as general mobile phone terminals. The mobile terminal  200  may further include a camera section and a contactless IC (integrated circuit) card functional section. 
       FIG. 4  is a view showing an example of a structure of an input word list  400  that is used as input history information of pairs of words successively input by the user in the past. The input word list  400  corresponds to the next-word candidate usage historical log information  123  shown in  FIG. 1 . The input word list  400  is formed in the manner that a node  401  is generated in units of a word input past, and respective nodes  401  thus generated are coupled together. The “word input in the past” refers to a word confirmed, such that a word unselected while presented as a next word candidate is not included into the category of “word input in the past.” Each node  401  is composed of a word  402  (“Word”), a number of used times  403  (NWP Candi_used_times), a number of unused times  404  (NWP Candi_unused_times), and a pointer  405 . The word  402  is a word input in the past. The number of used times  403  is the number of times a next word candidate (or, any one of multiple next word candidates, if any) for the word has been used. The number of unused times  404  is the number of times a next word candidate (or any one of multiple next word candidates, if any) for the word has been unused. The pointer  405  points or indicates a top of a next node  401 . The number of times the next word candidate has been used and the number of times the next word candidate has been unused will hereinbelow are referred to as “number of used times” and “number of unused times,” respectively. 
     The input history information is acquired in accordance with an existing technique, such that a practical technique for acquiring the log information is not limited by the present invention. Further, as words for prediction of next words, all words are not necessarily be targeted, but the words may be limited to either only words stored in a dictionary or predetermined ones thereof. 
     Next word candidates for respective words  402  are stored in the next word candidate database  121 . The next word candidate database  121  itself is of the type commonly known, but the structure thereof is not specifically limited by the present invention.  FIG. 5  shows an example of the general contents of the next word candidate database  121 . The next word candidate database  121  stores therein a word input in succession to an input word  501  in correlation therewith as a next word candidate  502 . While the number of next word candidates  502  is preferably a multiple number, an upper limit number may be preliminarily set. In this case, in the event that a new next word candidate is added after next word candidates have been stored to the upper limit number, a next word candidate with a low priority in a predetermined order of priority is erased. According to the predetermined order of priority, for example, a next word candidate corresponds to a word that is used least recently or at an oldest time most or having a lowest use frequency. In a method where the method of use frequency is used, information of the number of use times or use frequency is retained or stored. Alternatively, the method may be such that priority levels are provided to respective ones of multiple next word candidates for an input word  501 , and the respective next word candidates are sequentially presented to the user in that order of priority levels. More specifically, in the event that multiple next word candidates are present, a next word candidate with high priority level is arranged on a side where a highlight presentation, such as a cursor used for selection of a next word candidate, is set by default. 
     The next word prediction function of the present embodiment can be selectively set on/off.  FIGS. 6A to 6C , respectively, show examples of setting screens that are used for on/off setting of the next word prediction function. More specifically,  FIG. 6A  shows a mode in which an operation menu  601  is displayed.  FIG. 6B  shows a mode in which a submenu  602  is displayed when “Text-input related setting options (Text options)” is selected by the user on the operation menu  601 .  FIG. 6C  shows a mode in which an On/Off Setting Menu  603  of the next word prediction function is displayed when “Next word prediction” is selected on the submenu  602 . On the screen, when not desiring to use the next word prediction function, the user selects “Off.” Alternately, when desiring the next word prediction function, the user selects “On.” However, as described further below, a case can occur depending on the situation in which even when “On” is selected, the next word prediction function is inhibited. 
       FIGS. 7A to 7F  and  8 A to  8 E, respectively, are views of examples of screen transitions of character input on the mobile terminal  200  in the embodiment. In the respective examples, a specification screen for an appointment is shown. An application employing the present invention is not limited to the example application for specification of the appointment, but any one of arbitrary applications for, for example, e-mail, word processing, memo, schedule, telephone directory applications, which utilize character inputs. 
     On the respective shown screen, “a” displayed above a document input field  72  is indicative that an alphabet input mode is currently selected. In  FIG. 7A , the screen indicates a mode in which when, after input the word or phrase (the word in the present case) “Meeting” through the operation of the operation section  205 , the user has performed the operation of moving the cursor  73  to an input position of a next word, the next word candidate “with” is automatically displayed, as shown in  FIG. 7B , in accordance with past input historical logs. At this time point, however, since not confirmed by the user, the word candidate is displayed in a display mode displaying the word different from a normal word (with a brightness level lower than a normal brightness level. 
     In the present example, as shown in the next word candidate database  121  of  FIG. 5  generated in accordance with the past input history information, the words such as “with” and “at,” were input after the word “Meeting” in the past. In this case, of these input words, “with” having the highest priority level such as described above is automatically selected by the terminal as the next word candidate. 
     In the present embodiment, the next word prediction function is not inhibited when the number of used times (NWP Candi_used_times) of the next word candidate in the past is larger than or equal to the number of unused times (NWP Candi_unused_times) of the next word candidate in the past, the next word prediction function is exhibited when the number of used times is smaller than the number of unused times. As shown in an example of  FIG. 4 , in regard to the word “Meeting”, the number of used times (NWP Candi_used_times) of the next word candidate in the past is larger than the number of unused times (NWP Candi_unused_times) of the next word candidate in the past. Consequently, the next word candidate display is not inhibited. 
     With reference to  FIG. 7B , a downwardly pointing triangle mark (or arrow mark), that is, a reverse triangle mark  75 , is displayed immediately after the word “with.” This is indicative that other next word candidates are present, and multiple next word candidates (described further below by reference to  FIG. 7E ) will be displayed if the user carries out a downward specification operation on the operation section. In the example, since the word “with” matches a word intended to be input by the user, the user confirms the word by carrying out a predetermined operation (with a press or keystroke of an enter key). Then, as shown in  FIG. 7D , the cursor  73  is moved to the input position for a next word by a predetermined operation, such as entry of a keystroke of the “#” key. In this regard, the operational configuration may be such that that a keystroke of the “#” key concurrently represents the confirmation of the next word candidate “with” and the input of the space. Further, the operational configuration may be such that the reverse triangle mark  75  is not displayed when the number of next word candidates is only one. 
     With reference to  FIG. 7D , in regard to the work “with,” as shown in an example of  FIG. 4 , the number of used times (NWP Candi_used_times) of the next word candidate in the past is smaller than the number of unused times (NWP Candi_unused_times) of the next word candidate in the past. Consequently, the next word candidate display is inhibited. However, even in this event, the reverse triangle mark  75  is displayed immediately after the cursor  73 , whereby, if desired, the user can display a hidden next word candidate(s) by carrying out a downward specification operation. On the screen of  FIG. 7D , the hidden next word candidates are displayed in the form of a popup menu  77  as shown in  FIG. 7E . In the event that a target word is present in the popup menu  77 , when the user selects the target word by moving a word selection cursor  78  onto the target word, the selected next word candidate “the” is confirmed, as shown in  FIG. 7F . 
       FIG. 8A  shows a mode in which, when the space is input immediately after the word “the,” the next word candidate “gals” therefor is displayed. Suppose now that the next word candidate is not desired and hence the user has carried out a downward specification operation with the reverse triangle mark  75  to verify an other next word candidate. In this event, as shown in  FIG. 8B , the popup menu  77  is displayed. When the next word candidate “girls” is selected in the popup menu  77  and the space is input by the user, then, as shown in  FIG. 8C , the word “and” is displayed as a next word candidate for the word “girls”. As shown in an example of  FIG. 4 , in regard to the word “girls,” the number of used times (NWP Candi_used_times) of the next word candidate in the past is larger than the number of unused times (NWP Candi_unused_times) of the next word candidate in the past. Consequently, the next word candidate display is not inhibited. 
     On the screen of  FIG. 8C , suppose that in the event that a word the user intends to input in succession to the word “girls” is not “and,” and display of an other next word candidate is not desired. In this case, as shown in  FIG. 8D , a word (“to” in the example) the user desires to input is input from the operation section  205 . Thereby, the next word candidate “and” is erased, and the word “to” is instead input (displayed). Such an operation of erasure of a next word candidate by inputting a new word can be applied even in such a state where multiple next word candidates are displayed through the downward specification operation.  FIG. 8E  shows a mode in which “work” is displayed as a next word candidate for the word “to” through input of the space immediately after the word “to.” In this case also, the number of used times (NWP Candi_used_times) of the next word candidate in the past is larger than or equal to the number of unused times (NWP Candi_unused_times) of the next word candidate in the past. Consequently, the next word candidate display is not inhibited. 
     In the present invention, the method of inputting one word is not specifically limited. For example, the method may be such that, in the event the user inputs a word, all characters of the alphabet composing the word may be input one by one or may be input by using either an existing word predication technique or single-tap input technique. 
       FIGS. 9A to 9C , respectively, are examples of screen transitions in the case where a single-tap input technique is employed in the event the user inputs the word “to” on the screen of  FIG. 8D . More specifically,  FIG. 9A  shows a display example in the event that the user entered a keystroke of a key representing numeric value “8” (i.e., “8” key) of the tenkeys of the mobile terminal  200 . In this event, a popup menu  91  including alphabet characters “t,” “v,” and “u” allocated to the key as selection candidates is displayed.  FIG. 9B  shows a display example in the event that the user subsequently entered a keystroke of a “6” key of the tenkeys after the state shown in  FIG. 9A . In response to the keystrokes of the respective two tenkeys, the mobile terminal  200  displays in the popup menu  91  word candidates that can be acquired in accordance with combinations of characters allocated to the respective keys. In the present example, a respective “word” of two alphabet characters is shown. In the case where a further keystroke of a tenkey is successively entered, a dictionary of predetermined words is referenced, words respectively including character strings coupled with the displayed alphabet characters can be retrieved and displayed on the screen as selectors. 
       FIG. 9B  shows an example in the event that the user selected the word “to” from the selective items in the popup menu  91 . In this event, as shown in  FIG. 9C , the next word prediction function works. This corresponds to the screen transitions of  FIGS. 8D to 8E . 
       FIG. 10  shows a flow diagram of a process that is executed by the data processing section  101  ( FIG. 1 ) to thereby realize the operation of the next word prediction function as exemplified in the present embodiment. The process is execution upon completion of one word reception. One word reception is completed either upon completion of input of the space after input of a character string, i.e., a string of consecutive characters as explained above, or upon completion of an operation producing an result equivalent to the result of input of the space followed by the character string. 
     To begin with, a search operation that verifies whether an input word is present in an input word list  400  as shown in  FIG. 4  is executed (step S 11 ). If the word is not present in the input word list  400  (step S 12 : No), then a new node N ( 401  in  FIG. 4 ) is generated, and a new word is added into the node N (step S 13 ). Then, the number of used times  403  (NWP Candi_used_times) and number of unused times  404  (NWP Candi_unused_times) of the next word candidate in the node N is initialized to “0” (step S 14 ), the node N is added into the input word list  400 , and then the process ends. 
     If at step S 12  it has been verified that the word is present (i.e., step S 12 : Yes), then a node of the word matching with the input word is acquired (step S 16 ). Then, a comparison is made between the number of used times  403  (NWP Candi_used_times) and number of unused times  404  (NWP Candi_unused_times) of the node (step S 17 ). 
     If the number of unused times  404  (NWP Candi_unused_times) is larger than the number of used times  403  (NWP Candi_used_times), the next word candidate display is inhibited (step S 21 ). Thereafter, when next word candidate nonselection is confirmed (step S 23 : Yes), then the number of unused times  404  (NWP Candi_unused_times) is incremented (step S 24 ). Then, the process of  FIG. 10  ends. The next word candidate nonselection is confirmed either in the event that, for example, input of a character (inclusive of a period or the like) for a next word is started by the user with selection of neither a next word candidate nor an arrow key. 
     Subsequent to step S 21 , in the event that a keystroke of the arrow key (pointing downward, in the present example) is entered (step S 22 : Yes), a next word candidate is displayed (step S 18 ). That is, even in the event that at step S 17  the number of used times  403  (NWP Candi_used_times) is larger than or equal to the number of unused times  404  (NWP Candi_unused_times) (i.e., step S 17 : Yes), a next word candidate is displayed (step S 18 ). Although not shown, in a next word candidate process of step S 18 , a first word is displayed first, and then an other next word candidate(s) is displayed in accordance with an explicit specification (a keystroke of the downward arrow key, in the present example) entered by the user. 
     Subsequent to step S 18 , if any one of the displayed next word candidates is selected by the user (step S 19 : Yes), the number of used times  403  (NWP Candi_used_times) is incremented (step S 20 ), and the process of  FIG. 10  ends. 
     As described above, it is determined in accordance with the determination expression at step S 17  whether the number of used times  403  (NWP Candi_used_times) is larger than or equal to the number of unused times  404  (NWP Candi_unused_times). However, a determination expression using one of the parameters of the number of times to which a constant C is added may instead be used. More specifically, the following expression may be used: 
     NWP Candi_used_times+C&gt;NWP Candi_unused_times? In this case, the constant C is an integer. When the constant C is a positive integer, the next word candidate is likely to be displayed (in other words, display of the next word candidate is less likely to be inhibited). Conversely, when the constant C is a negative integer, the next word candidate is less likely to be displayed (in other words, display of the next word candidate is likely to be inhibited). The arrangement may be such that the user is permitted to directly or indirectly specify the constant C. The indirect specification is enabled in such a manner that, for example, multiple degrees of next word candidate displayability are provided to permit the user to select a degree of the displayability, and the numeric value of the constant C corresponding to the degree of displayability. With the constant C employed in the determination expression, the degree of the next word candidate displayability can be adjusted. 
     As above, while the preferred embodiment of the present invention has been described, various modifications and alterations can be made in addition to those described above. 
     For example, according to the preferred embodiment, in the event of next word candidate display for a certain input word, even when multiple next word candidates are present, only one next word candidate is first displayed, and other next word candidates are displayed in response to the request of the user. However, the operational configuration may be such that the multiple next word candidates (if present) are directly displayed. 
     While the character input device has been described with reference to the mobile phone terminal as an adaptation example, the character input device can be adapted to various other devices, such as fixed phone terminals and mobile terminals such as PDAs (personal digital assistants). 
     While the present invention is well suited for use in devices with a limited number of character keys, adaptation to devices having a so-called full keyboard is not excluded from the applicability of the invention. 
     Although only the alphabet characters have been described as word-composing characters, application to, for example, the Japanese kana and kanji characters is not excluded from the applicability of the present invention. 
     In the embodiment and examples, description has been made based on the contemplation that the keys as hardware keys, but the keys may be software keys allocated over a touchpanel. 
     While the shapes and constructions of the individual portions are described and shown in detail with reference to the embodiment and examples, they are merely practical examples for carrying out the present invention, so that they should not be construed as limiting the technical scope of the invention.