Patent Publication Number: US-2022219080-A1

Title: Method for providing a game, recording medium and server

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation application which claims the benefit of priority under 35 U.S.C. § 120 of U.S. patent application Ser. No. 16/890,256, filed Jun. 2, 2020, which is a continuation of U.S. patent application Ser. No. 16/133,274, filed Sep. 17, 2018 (U.S. patent Ser. No. 10/709,976), which is a continuation of U.S. patent application Ser. No. 15/684,241, filed Aug. 23, 2017 (now U.S. Pat. No. 10,086,281), which is a continuation of U.S. patent application Ser. No. 14/987,412, filed Jan. 4, 2016 (now U.S. Pat. No. 9,770,656), which is a continuation of U.S. patent application Ser. No. 14/109,704, filed Dec. 17, 2013 (now U.S. Pat. No. 9,272,222), which claims benefit of JP 2013-129889, filed on Jun. 20, 2013. The entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a method for providing a game, a recording medium, and a server. 
     BACKGROUND 
     In recent years, a server which provides a game to portable devices via a communication network has spread. The game provided by the server includes one in which a plurality of users can participate (a so-called “social game”), in which the users can not only battle and cooperate with each other but also communicate with each other. 
     As an example of such a social game, Patent Gazette No. JP5118261 describes a game in which a user battles with an enemy character by using a card (a so-called “card battle game”). In the card battle game, a user battles with an enemy character prepared on a game program by using a card while cooperating with another user. In such a game, a user can acquire an item by clearing a mission generated in the game, and can strengthen his/her card by using the item. 
     SUMMARY 
     Generally, a game includes a plurality of missions. The missions are the same for all users, and the number of missions to be presented is limited. Thus, the user is not able to try various missions. Moreover, items which can be acquired by clearing the missions are generally not clearly presented. Therefore, the user only tries all the missions to acquire the item he/she wants. Thus, a conventional game is not so interesting for the user, and the user may lose interest in continuing the game. 
     An object of the present invention is to increase chances for a user to select a mission, and to maintain and increase the user&#39;s interest in continuing a game. 
     Provided is a method for providing a game in which a plurality of missions is presented to a user device each time a certain period has elapsed from a server having a storage unit for storing user information relating to a plurality of users. The method includes the steps of generating a plurality of different missions for each of the plurality of users based on the user information stored in the storage unit, presenting a list of the generated missions for each of the users on the user device, and presenting an operational element for updating a mission included in the presented list to another mission, regardless of the elapse of the period in accordance with the progress of presented missions. 
     Preferably, the above method further includes the step of updating a mission included in the presented list to another mission generated for a corresponding user in response to operation of the operational element. 
     Preferably, in the above method, the storage unit stores information about another user associated with each of the plurality of users as the user information, and the step of presenting the list includes the step of presenting, along with the missions generated for a first user, a mission presented on a second user device of a second user associated with the first user, on the user device of the first user. 
     Preferably, the above method further includes the step of notifying the second user device that the mission presented on the second user device has also been presented on the user device of the first user. 
     Preferably, in the above method, the storage unit stores information about the time when each of a plurality of users has most recently played the game, as the user information, and the step of presenting the list includes the step of preferentially selecting, out of the plurality of other users associated with the first user, a device of a user who has not played the game for a longer time, as the second user device. 
     Preferably, in the above method, the step of presenting the list includes the step of presenting the mission presented on the second user device, on the user device of the first user only within a certain period. 
     Preferably, in the above method, the step of presenting the list includes the step of presenting the generated mission for each of the users and an item which can be acquired by the user by clearing the mission, on the user device in association with each other. 
     Provided is a non-transitory recording medium that has recorded a control program of a server, the server having a storage unit for storing user information relating to a plurality of users, for providing a game in which a plurality of missions is presented each time a certain period has elapsed to a user device. The control program causes the server to execute a process, the process including generating a plurality of different missions for each of the plurality of users based on the user information stored in the storage unit, presenting a list of the generated missions for each of the users on the user device, and presenting an operational element for updating a mission included in the presented list to another mission regardless of the elapse of the period in accordance with the progress of presented missions. 
     Provided is a server for providing a game in which a plurality of missions is presented each time a certain period has elapsed to a plurality of user devices. The server includes a storage unit for storing user information relating to a plurality of users, a generation unit for generating a plurality of different missions for each of the plurality of users based on the user information stored in the storage unit, and a listing unit for presenting a list of the missions for each of the users generated by the generation unit on the user devices. The listing unit presents an operational element for updating a mission included in the presented list to another mission, regardless of the elapse of the period in accordance with the progress of presented missions. 
     According to the above method for providing a game, the recording medium and the server, it is possible to increase the chances of a user selecting a mission, and maintaining and increasing the user&#39;s interest in continuing a game. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present optical device will be apparent from the ensuing description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an example of a schematic configuration of a game system; 
         FIG. 2  illustrates an example of a schematic configuration of the portable device; 
         FIG. 3  illustrates an example of a schematic configuration of the server; 
         FIGS. 4A to 4C  illustrate examples of data structures of the various types of tables. 
         FIGS. 5A to 5F  illustrate examples of a display screen of the portable device; 
         FIG. 6  illustrates an example of an operation sequence of the game system; 
         FIGS. 7A and 7B  illustrate an example of an operation flow of the server; and 
         FIG. 8  illustrates an example of an operation flow of the server. 
     
    
    
     DESCRIPTION 
     Hereinafter, with reference to the drawings, a method for providing a game, a recording medium, and a server will be described. It should be noted that the technical scope of the present invention is not limited to embodiments of the invention, but covers the invention described in the claims and its equivalent. 
     A game system described below provides a social game in which a plurality of users (players) can participate and a plurality of new missions is presented each time a certain period has elapsed. When the period is 24 hours, for example, a new mission is automatically presented to the users every day in the game system described below. “Mission” means a constituent element of a game called “quest”, “dungeon” or the like which allows the users to acquire an item and the like by clearing a mission. The mission is, for example, to explore a dungeon, battle with an enemy character, and acquire an item in the dungeon. The user plays the game while clearing a plurality of missions to collect desired items with his/her own portable device. 
     The game may be, for example, a mini game provided in a card battle game for battling with an enemy character by using a card. In this case, the item can be used to strengthen a card for a card battle, for example. The user can advantageously play the card battle by strengthening his/her own card by using the items collected in the plurality of missions. 
     Each of the portable devices requires a mission list for each of the users to select a mission of a server in response to an operation performed by the user. Consequently, the server presents a mission list generated for each of the users in which different missions are listed, to a corresponding portable device of the user. The server updates the missions included in the mission list to other missions in response to a request from the portable device. Thus, a user who has cleared the missions quickly can select a new mission without waiting, for example, 24 hours. Therefore, the chances of the user selecting the missions increase, making it possible to maintain and increase the user&#39;s interest in continuing the game. 
       FIG. 1  illustrates an example of a schematic configuration of a game system  1 . 
     The game system  1  includes at least one portable device  2  and a server  3 . The portable device  2  and the server  3  are connected to each other via a communication network, and are connected to each other, for example, via a base station  4 , a mobile communication network  5 , a gateway  6 , and the Internet  7 . A program to be executed by the portable device  2  (e.g., a browsing program) and a program to be executed by the server  3  (e.g., a game program) communicate with each other by using a communication protocol such as a Hypertext Transfer Protocol (HTTP). 
       FIG. 2  illustrates an example of a schematic configuration of the portable device  2 . 
     The portable device  2  is connected to the server  3  via the base station  4 , the mobile communication network  5 , the gateway  6 , and the Internet  7 , to communicate with the server  3 . The portable device  2  requests the progress of a game of the server  3  in response to an operation of an operation unit  23  (e.g., a button) by a user. The portable device  2  receives display data relating to the progress of the game from the server  3 , and displays the received display data. In order to implement the foregoing functions, the portable device  2  includes a device communication unit  21 , a device storage unit  22 , the operation unit  23 , a display unit  24 , and a device processing unit  25 . 
     While a multifunctional mobile phone (a so-called “smartphone”) may be assumed as being the portable device  2 , the present invention is not limited to this. The portable device  2  may be, for example, a mobile phone (a so-called “feature phone”), a personal digital assistant (PDA), a portable game machine, a portable music player, a tablet personal computer (PC) and the like, as long as the present invention is applicable thereto. 
     The device communication unit  21  includes a communication interface circuit including an antenna having a sensitivity band in a certain frequency band, and connects the portable device  2  to a wireless communication network. The device communication unit  21  establishes a wireless signal link with the base station  4  by a Wideband Code Division Multiple Access (WCDMA) (registered trademark) system or the like via a channel to be assigned by the base station  4 , and communicates with the base station  4 . The device communication unit  21  transmits data supplied from the device processing unit  25  to the server  3  or the like. The device communication unit  21  supplies the data received from the server  3  or the like to the device processing unit  25 . 
     The device storage unit  22  includes a semiconductor memory device, for example. The device storage unit  22  stores an operating system program, a driver program, an application program, data, and the like used for processing in the device processing unit  25 . For example, the device storage unit  22  stores, for example, an input device driver program for controlling the operation unit  23  and an output device driver program for controlling the display unit  24 , as the driver program. The device storage unit  22  stores a program and the like for retrieving and displaying display data relating to the progress of the game, as the application program. The device storage unit  22  stores display data, video data, image data and the like relating to the progress of the data, as the data. Further, the device storage unit  22  may store temporary data relating to certain processing. 
     The operation unit  23  may be any device capable of operating the portable device  2 , for example, a touch pad, a keyboard or the like. The user can input letters, numbers, and the like using the operation unit  23 . When operated by the user, the operation unit  23  generates a signal corresponding to the operation. The generated signal is supplied to the device processing unit  25  as an instruction from the user. 
     The display unit  24  may be any device capable of displaying a video, an image and the like, for example, a liquid crystal display and an organic electro-luminescence (EL) display. The display unit  24  displays a video, an image and the like corresponding to video data and image data supplied from the device processing unit  25 . 
     The device processing unit  25  includes one or a plurality of processors and their peripheral circuits. The device processing unit  25  is, for example, a central processing unit (CPU), and integrally controls an overall operation of the portable device  2 . The device processing unit  25  controls operations of the device communication unit  21 , the display unit  24 , and the like so that various types of processing of the portable device  2  are performed in an appropriate order in accordance with the programs stored in the device storage unit  22 , the operation of the operation unit  23 , and the like. The device processing unit  25  performs processing based on the programs (the operating system program, the driver program, the application program and the like) stored in the device storage unit  22 . The device processing unit  25  can execute a plurality of programs (application programs and the like) in parallel. 
     The device processing unit  25  includes at least a browsing executing unit  251 . Each of the units is a functional module implemented by a program to be executed by the processor included in the device processing unit  25 . Alternatively, each of the units may be provided as a firmware on the portable device  2 . 
     The browsing executing unit  251  retrieves and displays the display data relating to the progress of the game. In other words, a request to retrieve the display data relating to the progress of the game is transmitted to the server  3  via the device communication unit  21  in response to an instruction from the user. The browsing executing unit  251  receives corresponding display data from the server  3  via the device communication unit  21 . The browsing executing unit  251  generates drawing data based on the received display data. In other words, the browsing executing unit  251  interprets the received display data to specify control data and content data, lays out the specified content data according to the specified control data, and generates the drawing data. Then, the browsing executing unit  251  outputs the generated drawing data to the display unit  24 . 
       FIG. 3  illustrates an example of a schematic configuration of the server  3 . 
     The server  3  proceeds the game in response to a request from the portable device  2 . The server  3  generates the display data relating to the progress of the game, and transmits the generated display data to the portable device  2 . In order to implement the foregoing function, the server  3  includes a server communication unit  31 , a server storage unit  32 , and a server processing unit  33 . 
     The server communication unit  31  includes a communication interface circuit for connecting the server  3  to the Internet  7 , and communicates with the Internet  7 . The server communication unit  31  supplies the data received from the portable device  2  or the like to the server processing unit  33 . The server communication unit  31  transmits the data supplied from the server processing unit  33  to the portable device  2  or the like. 
     The server storage unit  32  includes at least one of a magnetic tape device, a magnetic disk device and an optical disk device, for example. The server storage unit  32  stores an operating system program, a driver program, an application program, data, and the like used for processing in the server processing unit  33 . The server storage unit  32  stores for example, a game program and the like for advancing the game and generating display data relating to its result, as the application program. The server storage unit  32  stores, as the data, a user table ( FIG. 4A ) for managing users, a mission table ( FIG. 4B ) for managing missions, and an item table ( FIG. 4C ) for managing items and the like. Further, the server storage unit  32  may store temporary data relating to certain processing. 
       FIGS. 4A to 4C  illustrate examples of data structures of the various types of tables. 
       FIG. 4A  illustrates an example of the data structure of the user table. The user table includes for each user, a user identifier (ID), a name, a level, a presented mission ID, an uncleared mission ID, a cleared mission ID, an acquired item ID, a previous finishing date and time, a friend ID and the like. The presented mission ID is an ID of each of the missions to be presented on a mission list for the target user. The uncleared mission ID is an ID of a mission which has not yet been cleared out of the missions presented on the mission list. The cleared mission ID is an ID of a mission that has already been cleared by the target user. The previous finishing date and time is information representing the date and time of the last time the target user ended the game. 
     The friend ID is an ID of another user in a friend status with the target user. In the game provided by the game system  1 , a friend status can be formed among the users. “Friend status” means a relationship constituted among users capable of jointly battling with an enemy character and sharing a mission in the game, as described below. A user can have a friend status with a plurality of users. However, an upper limit may be placed on the number of the other users whom a user can have a friend status with. A user c in a friend status with a user a is an example of other users associated with the user a. 
       FIG. 4B  illustrates an example of the data structure of the mission table. The mission table includes for each mission an ID of the mission, a name, a file name of image data, an ID of an enemy character to appear, an ID of an acquirable item and the like. 
       FIG. 4C  illustrates an example of the data structure of the item table. The item table includes for each item an ID of the item, a name, a file name of image data and the like. 
     The server processing unit  33  includes one or a plurality of processors and their peripheral circuits. The server processing unit  33  is for example, a CPU, and integrally controls an overall operation of the server  3 . The server processing unit  33  controls an operation of the server communication unit  31  or the like so that various types of processing of the server  3  are performed in an appropriate order in accordance with the programs stored in the server storage unit  32 . The server processing unit  33  executes processing based on the programs stored in the server storage unit  32  (the operating system program, the driver program, the application program and the like). The server processing unit  33  can execute the plurality of programs (the application program and the like) in parallel. 
       FIGS. 5A to 5F  illustrate examples of a display screen of the portable device  2  based on the display data generated by the server  3 . 
       FIGS. 5A and 5B  respectively illustrate mission lists  500  in an initial state of the user a and the user c. Each mission list  500  is displayed based on list display data received from the server  3 . On a screen of the user a, dungeons  1  to  3  and items A to C, which can be acquired by clearing the dungeons, are presented as a plurality of missions for the user a. On a screen of the user c, dungeons  4 ,  8 , and  9  and items D, H, and I, which can be acquired by clearing the dungeons, are presented as a plurality of missions for the user c. In such a manner, different missions are presented on the screens of different users. The number of missions to be presented may be any number, and in the following description, the number is set to three. 
     Each dungeon can be selected by pressing corresponding buttons  510 ,  520 , or  530  displayed on the screen. Each of the users confirms the items clearly presented on the mission list  500 , and operates the portable device  2  to select the mission in which the item desired by himself/herself can be acquired. When any one of the buttons  510 ,  520 , and  530  is pressed, the portable device  2  requests the server  3  to execute the corresponding mission via the device communication unit  21 . The item acquirable in each of the missions may include a plurality of types of items. In this case, the plurality of types of items may be presented on the mission list  500 . 
       FIGS. 5C and 5D  respectively illustrate mission lists  500  when the users a and c have selected the dungeons  1  and  4  in the presented missions and have cleared the dungeons  1  and  4 . On the mission list  500 , “cleared” is displayed on the button  510  corresponding to the dungeon  1  or  4 , indicating that the dungeon  1  or  4  has been cleared. It is not desirable in the progress of a game that an unrestricted number of identical items can be acquired. Therefore, when one mission is cleared, in principle, the server  3  disables a corresponding button (the button  510 ) so that the mission may not be executed again. Accordingly, the users a and c are not able to select the dungeons  1  and  4  again, respectively. 
     On the mission list  500  for the user a illustrated in  FIG. 5C , the mission (dungeon  4 ) which has been cleared by the other user c in a friend status with the user a, is also presented. Similarly, on the mission list  500  for the user c illustrated in  FIG. 5D , the mission (dungeon  1 ) which has been cleared by the other user a in a friend status with the user c, is also presented. For example, the user a can also select the mission which has been presented on the mission list  500  for the other user c in a friend status with the user a and has been cleared by the user c, by pressing a button  540  displayed on a lower part of the mission list  500 . A mission for a second user which has been presented together on a mission list for a first user, will be hereinafter referred to as a “shared mission”. When the button  540  is pressed, the portable device  2  also requests the server  3  to execute a corresponding mission via the device communication unit  21 . 
       FIG. 5E  illustrates the mission list  500  when the user a has cleared all the missions corresponding to the presented dungeons  1  to  3 . When a certain number of (three) missions presented for each user are all cleared, the server  3  enables an exchange button  550  for exchanging the presented missions. Thus, the user can operate the exchange button  550 . When the exchange button  550  is pressed, the portable device  2  requests the server  3  to exchange the missions via the device communication unit  21 . On the mission list  500 , the user a can operate the button  540 , because he/she has not yet cleared the dungeon  4  serving as the shared mission. 
       FIG. 5F  illustrates the mission list  500  when the exchange button  550  is pressed, and dungeons  5  to  7  are presented as new missions for the user a. On the mission list  500 , the buttons  510 ,  520 , and  530  are re-enabled, and are updated to ones corresponding to the dungeons  5  to  7 , respectively. On the other hand, when the missions have been exchanged, the exchange button  550  is disabled. Thus, the user a can select any one of the dungeons  4  to  7  by pressing the buttons  510  to  540 , just as on the mission list  500  illustrated in  FIG. 5A or 5C . 
     To implement the foregoing functions, the server processing unit  33  includes a control unit  331 , a mission generating unit  332 , a listing unit  333 , a mission executing unit  334 , a mission exchanging unit  335 , and a shared-mission specifying unit  336 . Each of the units is a functional module implemented by a program to be executed by the processor included in the server processing unit  33 . Alternatively, each of the units may be provided as firmware on the server  3 . 
     The control unit  331  controls the progress of a game, and instructs the mission generating unit  332 , the listing unit  333 , the mission executing unit  334 , the mission exchanging unit  335 , and the shared-mission specifying unit  336  to perform processing, as needed. 
     The control unit  331  interprets, when it has received a user authentication request from the portable device  2  via the server communication unit  31 , the received user authentication request, and specifies a user ID and a password. The control unit  331  instructs a user authenticating unit (not illustrated) to perform processing using the specified user ID and password as parameters. When the user authenticating unit has authenticated a user, the control unit  331  instructs the listing unit  333  to perform processing using the specified user ID as a parameter. The control unit  331  transmits list display data which has been returned by the listing unit  333 , to the portable device  2  via the server communication unit  31 . 
     The control unit  331  instructs, when it has received a mission execution request from the portable device  2  via the server communication unit  31 , the mission executing unit  334  to perform processing using the received mission execution request as a parameter. When the mission executing unit  334  communicates with the portable device  2  a plurality of numbers of times to end execution of a mission, the control unit  331  deletes the ID of the mission from the “uncleared mission ID” for the target user in the user table, and adds the deleted ID to the “cleared mission ID” for the target user in the user table. Moreover, the control unit  331  calls the listing unit  333  again at this time, and instructs the listing unit  333  to perform processing. The control unit  331  transmits the list display data which has been returned by the listing unit  333 , to the portable device  2 . 
     The control unit  331  instructs, when it has received a mission exchange request from the portable device  2  via the server communication unit  31 , the mission exchanging unit  335  to perform processing using the received mission exchange request as a parameter. When the mission exchanging unit  335  terminates mission exchange processing, the control unit  331  instructs the listing unit  333  to perform processing again. The control unit  331  transmits the list display data, which has been returned by the listing unit  333 , to the portable device  2 . The mission generating unit  332  generates a plurality of different missions for each user in response to a request issued by the mission exchanging unit  335 . The mission generating unit  332  selects, for each of a geography of a dungeon to be explored by the user, an enemy character that appears in the dungeon, and an item acquirable in the dungeon, one of a plurality of candidates to constitute the mission. Thus, the mission generating unit  332  generates a plurality of missions, which differ in a combination of a geography of a dungeon, an appearing enemy character, and an acquirable item, for example. 
     If, for example, the game system  1  provides a game including ten missions in all to each of the users, the ten missions differ depending on the user. Thus, in a general game, a plurality of identical missions is provided to all of the users, but in the game provided by the game system  1 , different missions are provided to each user. The mission generating unit  332  may generate, for example, individual missions at random or generate different missions for each of the users according to any regularity. 
     The mission generating unit  332  refers to the user table using the user ID as a key, specifies the level of the target user, and then generates missions. The higher the level is, the higher the degree of difficulty of the generated mission is. The mission having a high degree of difficulty is, for example, a mission in which a stronger enemy character appears and in which the user consumes more physical strength to clear. The mission generating unit  332  sets items acquirable in each of the missions. The higher the degree of difficulty of the mission is, the more valuable the items to be acquired in the mission are and the larger the number of the items to be acquired in the mission becomes. The mission generating unit  332  adds information about the generated mission to the mission table. 
     The listing unit  333  presents a list of the missions which have been generated by the mission generating unit  332 , to the portable device  2  of each of the users via the server communication unit  31 . In order to achieve such function, the listing unit  333  generates list display data for displaying the mission list  500  illustrated in  FIGS. 5A to 5F  on the portable device  2 . Specifically, the listing unit  333  refers to the user table using the user ID as a key, and specifies the IDs of (e.g., three) missions generated for the target user and to be presented on the mission list  500  and whether the missions have been cleared. The listing unit  333  causes the shared-mission specifying unit  336  to specify a shared mission to be presented on the mission list  500 . Further, the listing unit  333  refers to the mission table using each of the specified mission IDs as a key, and specifies the item acquirable in each mission. 
     The listing unit  333  generates list display data so that names of respective missions, an image, items acquirable by clearing the missions, data for indicating whether each of the missions has been cleared, and buttons for selecting respective missions are displayed. The listing unit  333  enables, for an uncleared mission, a button of the mission, and disables, for a cleared mission, a button of the mission. Particularly for a shared mission, a button is displayed so that the user can select the mission only within a certain effective time to prevent the number of missions to be presented from increasing unlimitedly. 
     Further, the listing unit  333  presents an operational element for updating the missions included in the mission list  500  to other missions according to the progress of the presented missions. Specifically, the listing unit  333  enables, when the three missions currently presented are all cleared missions, the exchange button  550  illustrated in  FIG. 5E  for exchanging the missions. The listing unit  333  may disable the exchange button  550  when at least one of the missions currently presented has been cleared. The exchange button  550  is an example of the operational element. 
     The mission executing unit  334  communicates with the portable device  2  a plurality of times to execute the mission when receiving the mission execution request from the portable device  2  caused by the user operating a button corresponding to one mission on the mission list  500 . The mission may be executed by the device processing unit  25  in the portable device  2  without providing the mission executing unit  334  in the server  3 . 
     The mission exchanging unit  335  exchanges, when receiving a mission exchange request from the portable device  2  caused by the user operating the exchange button  550  in the mission list  500 , a mission in the mission list  500  for another mission generated by the mission generating unit  332  for the target user. 
     Specifically, the mission exchanging unit  335  causes, when the user operates the exchange button  550  in the mission list, the mission generating unit  332  to generate a new mission for the user. The mission exchanging unit  335  deletes the ID of the mission from the “presented mission ID” for the target user in the user table, and adds the ID of the newly generated mission to the “uncleared mission ID” and the “presented mission ID” for the target user. When the mission exchanging unit  335  exchanges the missions, the possibility that the user can select a mission he/she likes becomes higher, increasing the user&#39;s will to continue the game. 
     As described above, in the game system  1 , a plurality of new missions are presented each time a certain period (e.g., 24 hours) has elapsed. However, the mission exchanging unit  335  exchanges the missions presented on the mission list  500  regardless of whether the certain period has elapsed, in response to the user operating the exchange button  550 . In other words, since the exchange button  550  is disabled each time the three presented missions are cleared, the user who has cleared the missions quickly can select a new mission without waiting, for example, 24 hours. 
     The mission exchanging unit  335  may perform exchange processing not only for the missions generated for each of the users but also for a shared mission. The missions to be exchanged by the mission exchanging unit  335  may include a mission cleared once by the user. In other words, the same mission may be presented again by exchanging the missions. In this case, the user can re-execute the mission that has been cleared once. 
     The shared-mission specifying unit  336  specifies a mission presented to a portable device of a second user in a friend status with a first user so that the shared mission is presented on a portable device of the first user. A first user (himself/herself) and one of second users (other users) are described below as the user a and the user c, respectively. 
     The shared-mission specifying unit  336  first refers to the user table using the user ID of the user a as a key, and specifies other users in a friend status with the user a. The shared-mission specifying unit  336  may present shared missions for all the users in a friend status with the user a on the mission list  500  for the user a. When the number of users is large, however, the shared missions are presented only for the number of users within a certain upper limit. The shared-mission specifying unit  336  sets the upper limit of the number of users for which the shared missions are presented to four, for example, and makes respective missions cleared by the four users as the shared missions. As the four users, the shared-mission specifying unit  336  selects, out of the users in a friend status with the user a, the two users whose previous finishing date and time are most and second most recent and two users whose previous finishing date and time are the oldest and the second oldest. In other words, the shared-mission specifying unit  336  selects the user who has most recently played the game and the user who has not recently played the game as the other users for which the shared mission is to be presented on the mission list  500  for the user a. 
     The shared-mission specifying unit  336  refers to the user table using the user ID of the selected other user as a key, selects one of cleared missions for the user, and specifies the selected cleared mission as a shared mission. A shared mission is selectable by the user only within a certain effective time. Thus, for each of the users, the shared-mission specifying unit  336  specifies one mission which has most recently been cleared by the user, for example, as a shared mission. Alternatively, the shared-mission specifying unit  336  may select one of the uncleared missions for the user and specify the selected uncleared mission as a shared mission. 
     Presenting a shared mission on the mission list  500  may enable a user to acquire a desired item in the shared mission although the desired item is not able to acquire in his/her own mission, for example. A user in a friend status with more users can more easily acquire items because the number of missions to be shared increases. When the shared missions are presented on the mission list  500 , therefore, a chance for the user to select the missions further increases, which increases the user&#39;s will to continue the game. 
     A dungeon in which an item desired by a user can be acquired may preferentially be displayed. For example, to enable the user to reliably acquire the item he/she desires, a mission which the user was unable to clear in the past, is managed in the server  3 , and the shared-mission specifying unit  336  may preferentially extract, out of a plurality of candidates of shared missions, the mission that the user was unable to clear in the past. 
     A mission and an item which can be acquired when the mission has been cleared are managed in association with each other in the server  3  (the mission table illustrated in  FIG. 4B ). When a user designates a desired item in advance, the shared-mission specifying unit  336  may be controlled to preferentially extract, out of a plurality of candidates of shared missions, a mission in which the item designated by the user can be acquired. 
     Since the mission generating unit  332  generates missions corresponding to the level of a user, a shared mission is a mission corresponding to the level of another user in a friend status with the user a. If another user has a higher level than that of the user a, for example, a mission which is not presented at the level of the user a may be presented as a shared mission. In this case, it is difficult for the user a to clear the shared mission, but if the user a clears the shared mission, the user a can acquire more items than when the user a clears a mission generated for himself/herself. 
     In order to present missions with a higher level of difficulty, the shared-mission specifying unit  336  may set a mission which has been cleared by the user having a higher level than that of the user a out of the plurality of users in a friend status with the user a, as a shared mission. Alternatively, the shared-mission specifying unit  336  may set, as a shared mission, a mission for another user in a certain relationship other than the friend status such as a user designated by the user a. 
     Further, the number of shared missions to be presented is not limited to one but may be plural per user in a friend status with the user a. For example, a parameter such as a degree of intimacy may be set between a user and another user in a friend status therewith, and the number of shared missions to be presented and the type and the number of items acquirable in the shared missions may be made different depending on the parameter. 
     The shared-mission specifying unit  336  push-notifies the portable device of the second user via the server communication unit  31  that a mission presented on the portable device of the second user (user c) in a friend status with the first user (user a) has also been presented on the portable device of the first user. In this case, the shared-mission specifying unit  336  clearly presents the user name of the first user (user a) and push-notifies the second user of the user name. Thus, a user becomes more interested and motivated to the game when “Mission has been shared by user a”, for example, is notified to clearly present a one-to-one relationship between users than when “New mission has started” is simply notified simultaneously from the server  3  to users. Particularly, the shared-mission specifying unit  336  selects a user who has not recently played the game as the second user, to encourage the user to participate in the game. 
       FIG. 6  illustrates an example of an operation sequence of the game system  1 . The operation sequence described below is executed mainly by the device processing unit  25  and the server processing unit  33  based on programs previously stored in the device storage unit  22  and the server storage unit  32 , in cooperation with each of the units in the portable device  2  and the server  3 . 
     The user a instructs the device processing unit  25  to execute a program for retrieving and displaying display data relating to the progress of the game via the operation unit  23 . The device processing unit  25  starts processing based on this program. In other words, the browsing executing unit  251  to be implemented by the program transmits, when the user a has input a user ID and a password via the operation unit  23 , a user authentication request including the input user ID, password and the like to the server  3  via the device communication unit  21  (step S 600 ). 
     The control unit  331  interprets, when receiving the user authentication request via the server communication unit  31  from the portable device  2 , the received user authentication request and specifies the user ID and the password. The control unit  331  instructs a user authenticating unit (not illustrated) to perform processing using the specified user ID and password as parameters (step S 602 ). The control unit  331  instructs, when the user authenticating unit has authenticated the user, the listing unit  333  to perform processing using the specified user ID as a parameter (step S 604 ). 
     The control unit  331  transmits list display data which has been returned by the listing unit  333  to the portable device  2  via the server communication unit  31  (step S 606 ). The browsing executing unit  251  in the portable device  2  generates, when receiving the list display data from the server  3  via the device communication unit  21 , drawing data based on the received list display data. The browsing executing unit  251  outputs the generated drawing data to the display unit  24  to display a mission list thereon (step S 608 ). 
     When an execution instruction of a mission has been input on the mission list by the user via the operation unit  23 , the browsing executing unit  251  transmits a content of the instruction and the user ID to the server  3  via the device communication unit  21  (step S 610 ). The control unit  331  of the server  3  instructs, when receiving the mission execution request from the portable device  2  via the server communication unit  31 , the mission executing unit  334  to perform processing using the received mission execution request as a parameter (step S 612 ). 
     When the mission executing unit  334  terminates the mission execution processing, the control unit  331  instructs the listing unit  333  to perform processing (step S 614 ), just as in step S 604 , and transmits list display data which has been returned by the listing unit  333  to the portable device  2  (step S 616 ), just as in step S 606 . The browsing executing unit  251  of the portable device  2  causes the display unit  24  to display a mission list on the display unit  24  (step S 618 ), just as in step S 608 . 
     When an exchange instruction of the missions has been input on the mission list by the user via the operation unit  23 , the browsing executing unit  251  transmits a content of the instruction and the user ID to the server  3  via the device communication unit  21  (step S 620 ). The control unit  331  of the server  3  instructs, when receiving a mission exchange request from the portable device  2  via the server communication unit  31 , the mission exchanging unit  335  to perform processing using the received mission exchange request as a parameter (step S 622 ). 
     The control unit  331  instructs, when the mission exchanging unit  335  terminates the mission exchange processing, the listing unit  333  to perform processing (step S 624 ), just as in step S 604 . The control unit  331  transmits list display data which has been returned by the listing unit  333  to the portable device  2  (step S 626 ), just as in step S 606 . The browsing executing unit  251  of the portable device  2  causes the display unit  24  to display a mission list (step S 628 ). Subsequently, processing is similarly performed. 
       FIG. 7A  illustrates an example of an operation flow of the listing unit  333 . 
     The listing unit  333  first specifies an uncleared mission for a target user (step S 700 ). In this case, the listing unit  333  refers to the user table using the user ID of the target user as a key, and specifies the three presented mission IDs and the uncleared mission IDs. Further, the listing unit  333  refers to the mission table using each of the specified presented missions IDs as a key, and also specifies the item acquirable in the corresponding mission. 
     If all the three missions which have been specified in step  700  have been cleared (i.e., there is no uncleared mission ID) (YES in step S 702 ), the listing unit  333  disables the exchange button  550  (step S 704 ). On the other hand, if the three missions which have been specified in step S 700  includes an uncleared mission (NO in step S 702 ), the listing unit  333  keeps the exchange button  550  disabled without executing step S 704 . 
     The listing unit  333  then causes the shared-mission specifying unit  336  to specify a shared mission to be presented on the mission list (step S 706 ). The listing unit  333  generates list display data for displaying a mission list including names of respective missions, images, acquirable items, data for indicating whether each of the missions has been cleared, and buttons for selecting respective missions (step S 708 ). The listing unit  333  returns the list display data to the control unit  331  (step S 710 ), and then terminates the processing. 
     In the operation flow illustrated in  FIG. 7A , the shared mission is specified in step S 706  each time list retrieval processing is performed. However, since the shared-mission specifying unit  336  specifies the mission which has most recently been cleared by each user as the shared mission, for example, even if step S 706  is executed, the shared mission presented on the mission list may not be changed. 
       FIG. 7B  illustrates an example of an operation flow of the mission exchanging unit  335 . 
     The mission exchanging unit  335  first causes the mission generating unit  332  to newly generate missions for the target user (step S 720 ). The mission exchanging unit  335  updates the presented mission IDs for the target user in the user table with IDs of the missions newly generated (step S 722 ). Further, the mission exchanging unit  335  adds the IDs of the missions newly generated to the uncleared mission IDs for the target user in the user table (step S 724 ). Then, the mission exchanging unit  335  terminates the processing. 
       FIG. 8  illustrates an example of an operation flow of the shared-mission specifying unit  336 . 
     The shared-mission specifying unit  336  first refers to the user table using the user ID of a target user as a key, and extracts users in a friend status with the target user (step S 800 ). The shared-mission specifying unit  336  selects one of the users in the friend status, who have been extracted in step S 800 , in accordance with a certain criterion, for example, the user whose previous finishing date and time is most recent or whose previous finishing date and time is the oldest (step S 802 ). The shared-mission specifying unit  336  refers to the user table using the user ID of the selected other user as a key, and specifies cleared missions for the selected user (step S 804 ). Further, the shared-mission specifying unit  336  selects, out of the cleared missions which have been specified in step S 804 , the mission that has most recently been cleared, and specifies the selected mission as a mission to be shared (step S 806 ). 
     When the number of users for which the shared missions are presented has not reached a certain upper limit yet (NO in step S 808 ), the processing returns to step S 802 . On the other hand, when the number of users for which the shared missions are presented has reached the upper limit (YES in step S 808 ), the shared-mission specifying unit  336  returns the missions specified thus far as shared missions to the listing unit  333  (step S 810 ), and terminates the processing. 
     As has been described above, in the game system  1 , the mission generating unit  332  generates separate missions and provides the generated missions to each of the users, and the mission exchanging unit  335  exchanges the missions on the mission list so that a chance for the user to select the missions increases, making it possible to maintain and increase the user&#39;s will to continue the game. 
     In the operation flow illustrated in  FIG. 7A , once the exchange button  550  is pressed, the exchange button  550  will not be disabled as long as the presented missions are all cleared. However, even after being pressed, the exchange button  550  may be pressed many times within a certain period (e.g., 24 hours). 
     A computer program for causing a computer to execute the respective functions of the device processing unit  25  and the server processing unit  33  may be provided in a form recorded on a computer readable recording medium such as a magnetic recording medium or an optical recording medium. 
     It should be understood that various changes, substitutions, and modifications can be made to the present invention by those skilled in the art without departing from the spirit and scope of the present invention. 
     The preceding description has been presented only to illustrate and describe exemplary embodiments of the present invention. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. The invention may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope.