Patent Publication Number: US-11023097-B2

Title: Mobile terminal and message-based conversation operation method for grouping messages

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation application of prior application Ser. No. 13/729,723, filed on Dec. 28, 2012, and was based on and claimed priority under 35 U.S.C. § 119(a) of a Korean patent application filed on Jan. 5, 2012 in the Korean Intellectual Property Office and assigned Serial No. 10-2012-0001354, the entire disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a conversation operation in a mobile terminal. More particularly, the present invention relates to an apparatus and method for a message-based conversation operation that collects messages from conversations made during utilization of messaging services and groups the collected messages for easy management. 
     2. Description of the Related Art 
     A mobile terminal is a terminal that supports call related functions while providing mobility for the user. Recently, mobile terminals have entered into widespread use because of their convenience and portability thereof. Mobile terminals may provide various input schemes to support user functions. For example, when a mobile terminal has a touchscreen composed of a touch panel and a display part, the user may select a specific image displayed on the display part through the touch panel. In other words, the mobile terminal may generate a touch event corresponding to a user action and execute an application program according to the touch event. 
     With recent advances in communication networks, the use of messaging services has rapidly increased. For example, users may conduct an instant conversation through dialog windows that display sent and received messages. 
     Although screen sizes of mobile terminals have increased, the size of the screen is inherently limited due to mobility requirements. Thus, users may still experience inconvenience in manipulating dialog windows containing sent and received messages. For example, when a user of a mobile terminal sends and receives many messages in real-time during a message-based conversation, the mobile terminal is only able to display the latest message because all the exchanged messages cannot be displayed in a single screen having size limitations. To refer to the previous messages, the user must scroll the dialog window. However, because a rapid scroll operation causes rapid message display, which may hinder the user&#39;s understanding of message contents, the user must slowly scroll the dialog window. This may cause a delay in finding a desired one of the previous messages, and disrupt the flow of conversation. 
     Therefore, a need exists for an apparatus and method for classifying messages sent and received during a conversation into groups and storing the messages such that the stored messages may be easily searched and utilized in various ways. 
     The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention are to address the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a mobile terminal and message-based conversation operation method for the same wherein messages sent and received during a conversation are classified into groups and stored so that the stored messages may be easily searched and utilized in various ways. 
     In accordance with an aspect of the present invention, a method for message-based conversation operation is provided. The method includes generating message groups by classifying one or more messages exchanged during a message-based conversation according to preset conditions, storing the generated message groups; and outputting display items corresponding to the stored message groups in a dialog window for the message-based conversation. 
     In accordance with another aspect of the present invention, a mobile terminal capable of supporting a message-based conversation function is provided. The mobile terminal includes a communication unit for sending and receiving messages for the message-based conversation function, a control unit for generating message groups by classifying one or more messages exchanged during a message-based conversation according to preset conditions, a storage unit for storing the generated message groups, and a display unit for outputting display items corresponding to the stored message groups in a dialog handling window for the message-based conversation. 
     Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of a mobile terminal according to an exemplary embodiment of the present invention; 
         FIG. 2  illustrates an exemplary configuration of a control unit of the mobile terminal in  FIG. 1 ; 
         FIG. 3  is a flowchart of a conversation operation method according to an exemplary embodiment of the present invention; 
         FIG. 4  illustrates screen representations of individual messages and message groups in conversations according to an exemplary embodiment of the present invention; 
         FIG. 5  illustrates screen representations for an ongoing conversation with manipulation of message groups according to an exemplary embodiment of the present invention; 
         FIG. 6  illustrates screen representations for splitting a message group according to an exemplary embodiment of the present invention; 
         FIG. 7  illustrates screen representations for merging message groups according to an exemplary embodiment of the present invention; 
         FIG. 8  illustrates screen representations for moving a message group according to an exemplary embodiment of the present invention; 
         FIG. 9  illustrates screen representations for sorting message groups according to an exemplary embodiment of the present invention; 
         FIG. 10  illustrates screen representations for searching or browsing message groups according to an exemplary embodiment of the present invention; 
         FIG. 11  illustrates a display item of icon type in a first form for depicting message group information according to an exemplary embodiment of the present invention; 
         FIG. 12  illustrates a display item of quick view type in a first form for depicting message group information according to an exemplary embodiment of the present invention; 
         FIG. 13  illustrates screen representations for searching display items of message groups according to an exemplary embodiment of the present invention; 
         FIG. 14  illustrates additional screen representations for searching display items of message groups according to an exemplary embodiment of the present invention; 
         FIG. 15  illustrates a display item of icon type in a second form for depicting message group information according to an exemplary embodiment of the present invention; and 
         FIG. 16  illustrates a display item of quick view type in a second form for depicting message group information according to an exemplary embodiment of the present invention. 
     
    
    
     Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
     The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
     It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
     Next, a description is given of the configuration and operation of the present invention. However, it is to be understood that the description is of exemplary embodiments only and that the present invention is not limited to or by the following description. That is, various changes and modifications are possible on the basis of the following description. 
       FIG. 1  is a block diagram of a mobile terminal according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , the mobile terminal  100  may include a communication unit  110 , an input unit  120 , an audio processing unit  130 , a display unit  140 , a storage unit  150 , and a control unit  160 . 
     The mobile terminal  100  having the above configuration collects messages during a conversation and classifies the collected messages according to preset conditions or user input conditions into message groups. The mobile terminal  100  arranges message groups in a preset form in a dialog window so that the user may easily find a desired message group. When a message group is selected, the mobile terminal  100  may provide a quick view screen for displaying some messages in the selected message group or a detailed view screen for displaying all messages in the selected message group in a full screen format, so that the user may identify message contents in outline or in detail. The mobile terminal  100  enables the user to start a new conversation on the basis of a selected message group. The mobile terminal  100  may output, for a message group, a display item indicating the importance of the message group, and permit the user to insert an information element describing the message group into the display item. As described above, during a message-based conversation, the mobile terminal  100  supports a message manipulation function for creation, display, management, and searching of message groups. 
     The communication unit  110  establishes a communication channel for voice, video and data communication under the control of the control unit  160 . That is, the communication unit  110  may establish a communication channel for a voice call, a data call and a video call to a mobile communication system. More particularly, the communication unit  110  may establish a communication channel to exchange messages for message-based conversation in a messaging service such as text messaging, multimedia messaging or instant messaging. Such a communication channel may include a transmission channel to send a message to a second terminal and a reception channel to receive a message from the second terminal. Here, the transmission channel and the reception channel may use different frequency bands or use the same frequency band. 
     The communication unit  110  supports message transmission and reception during a conversation, and may send and receive a message group to and from a corresponding terminal according to user selection. Here, to send and receive a message group, the communication unit  110  may use address information of the corresponding terminal indicated by the user. Address information may be saved in advance or newly saved as requested or confirmed by the user. 
     The input unit  120  includes a plurality of alphanumeric and function keys for inputting alphanumeric information and for setting various functions. The function keys may include direction, side, and shortcut keys associated with specific functions. The input unit  120  generates key signals for user settings and for controlling operations of the mobile terminal  100 , and forwards the key signals to the control unit  160 . More particularly, the input unit  120  may generate various input signals needed for the message-based conversation function. For example, the input unit  120  may generate an input signal for selecting and activating a conversation function application, an input signal for creating a message during a conversation, and an input signal for receiving a message during the conversation. The input unit  120  may generate input signals for classifying sent and received messages into message groups, for splitting a selected message group, for merging message groups, and for moving and arranging message groups according to user manipulation. The input unit  120  may also generate input signals for finding a desired message group, for selecting and reading a message group, for starting a new conversation with another user on the basis of a selected message group, and for browsing message groups using a quick view screen or a detailed view screen. 
     Some input signals may be touch events generated by a touch panel  143  of the display unit  140  (described later). Hence, the input means may include not only the input unit  120  containing key buttons but also the touch panel  143 . When the display unit  140  is a touchscreen, the input unit  120  may be realized using a QWERTY key map, a Dvorak key map, a 3*4 key map, a 4*3 key map, and the like, which are displayable on the display unit  140 . 
     The audio processing unit  130  includes a speaker (SPK) for outputting audio data during a call, outputting audio data contained in a message and outputting audio data stored in the storage unit  150 , and a microphone (MIC) for collecting an audio signal such as a voice signal during a call. More particularly, the audio processing unit  130  may output a sound effect indicating message reception during a conversation, output a sound effect indicating message selection, and generate sounds corresponding to message contents according to user settings. These functions may be turned off according to user settings. 
     The display unit  140  includes a display panel  141  and the touch panel  143 . In an exemplary implementation, the touch panel  143  may be placed on the front surface of the display panel  141 . 
     The display panel  141  displays various menus of the mobile terminal  100 , information input by the user, information to be provided to the user, and the like. For example, the display panel  141  may output various screens related to usage of the mobile terminal  100 , such as an idle screen, a message composition screen, a call handling screen, and the like. The display panel  141  may be realized using Liquid Crystal Display (LCD) devices, Organic Light Emitting Diodes (OLED), and the like. The display panel  141  may be placed above or below the touch panel  143 . 
     More particularly, the display panel  141  may output various screens or windows during a conversation. For example, the display panel  141  may output a screen for writing a message in a conversation, a screen for sending the written message, a screen for receiving a message, a screen for outputting one or more message groups as display items in specific forms, a screen for quickly viewing message groups, a screen for viewing message groups in detail, a screen for displaying display items associated with message groups, and the like. The display panel  141  may output a screen for splitting a message group, a screen for merging message groups, a screen for moving message groups, a screen for arranging message groups, and the like. 
     The touch panel  143  is placed above and/or below the display panel  141 , and may generate a touch event according to contact by an object like a finger and forward the generated touch event to the control unit  160 . Sensing elements constituting the touch panel  143  are arranged in a matrix form, and send information on the coordinates and type of a touch event occurring on the touch panel  143  to the control unit  160 . 
     More particularly, the touch panel  143  may configure various touch regions to generate touch events during a message-based conversation. For example, the touch panel  143  may allocate character regions at suitable portions of a message composer so that the user may write a message by touching the character regions. The touch panel  143  may generate various touch events for creating, managing, and searching message groups according to user actions and send the touch events to the control unit  160 . Touch events generated by the touch panel  143  for manipulating message groups are described in more detail later with reference to the drawings. 
     The storage unit  150  may store application programs realizing functions of the mobile terminal  100 , application programs realizing user functions, key maps and menu maps for proper operation of the display unit  140 , and the like. The key maps and menu maps may take various forms. More particularly, the storage unit  150  may include a conversation function application  151  for realizing message-based conversation and a conversation information database  153  for maintaining messages and message groups in conversations. 
     The conversation function application  151  supports creation, display, management and searching of message groups in conversations. The conversation function application  151  may be activated according to user selection or configuration settings and may generate a message and display a received message in a conversation after activation. The conversation function application  151  may classify multiple messages into message groups in response to an input signal such as a touch event, and output display items corresponding to the message groups to the display unit  140 . Here, the display items may be output to the current screen by default or output to the display unit  140  upon a request, such as scrolling, according to user settings. The conversation function application  151  may split a selected message group, merge message groups, move message groups, rearrange message groups, and the like according to input signals. The conversation function application  151  may output a quick view screen or a detailed view screen during a search of message groups. 
     The conversation information database  153  stores various messages and message groups generated in conversations. The conversation information database  153  stores information on display items associated with message groups, information on segmentation of a message group, information on merging of message groups, information on searching of message groups, and the like. Display items associated with message groups are described in more detail later with reference to the drawings. 
     The control unit  160  controls the supply of power to the components of the mobile terminal  100 . For example, the control unit  160  controls the supply of power for initialization of the mobile terminal  100 . The control unit  160  controls various signal flows between the components to support the message-based conversation function. 
       FIG. 2  illustrates an exemplary configuration of a control unit of the mobile terminal in  FIG. 1 . 
     Referring to  FIG. 2 , the control unit  160  may include a touch event collector  161 , a message group manager  163 , and a conversation function manager  165 . 
     The touch event collector  161  collects touch events generated by the touch panel  143  of the display unit  140 . For example, the touch event collector  161  collects a touch event generated by the touch panel  143  after activation of the message-based conversation function. When a touch event is collected, the touch event collector  161  may send information on the type and coordinates of the touch event to the message group manager  163 . In this process, the touch event collector  161  may configure touch regions on the touch panel  143 . For example, when a message group is created, a display item corresponding to the message group may be displayed on the display panel  141  and the touch event collector  161  may configure a touch region on the touch panel  143  so that the user may select the display item by touching the touch region. 
     The message group manager  163  supports creation, display, management, searching, and the like of message groups. Under control of the conversation function manager  165 , the message group manager  163  may classify enrolled messages according to a preset condition or user input to thereby generate message groups. The message group manager  163  may create display items corresponding to the message groups and output the display items to the display panel  141  according to user selection. Here, a display item may be of a fast view type or an icon type. A display item of the fast view type shows portions of messages present in the corresponding message group. A display item of the icon type shows information derived from messages present in the corresponding message group or information entered by the user. 
     The message group manager  163  may split a message group, merge message groups, and move or rearrange display items on the display panel  141  according to user input. When a display item is selected, the message group manager  163  may output a quick view screen or a detailed view screen, which shows a message group associated with the selected display item, to the display panel  141 . Manipulation of message groups by the message group manager  163  is described in more detail later with reference to the drawings. 
     The conversation function manager  165  invokes the conversation function application  151  stored in the storage unit  150  for execution in response to an input signal for activating a message-based conversation, retrieves requested information from the conversation information database  153 , and outputs the retrieved information to the display unit  140 . For example, when the conversation function is selected for activation, the conversation function manager  165  controls the display unit  140  to output a message composer. When a message is written, the conversation function manager  165  may send the written message to a mobile terminal of a selected counterpart. When a conversation counterpart is selected, the conversation function manager  165  may output messages, which are most recently sent to and most recently received from the selected counterpart, to the display unit  140 . When the most recently exchanged messages are grouped into a message group, the conversation function manager  165  may output a display item corresponding to the message group to the display unit  140 . 
     The conversation function manager  165  may display a message received from another mobile terminal on the display panel  141  and store the received message in the conversation information database  153 . The conversation function manager  165  manages transmission and reception of messages in a message-based conversation, and supports the message group manager  163  to classify sent and received messages into message groups and to display, search and manage the message groups. 
     The conversation function manager  165  may initiate a new message-based conversation on the basis of an already stored message group under the direction of the message group manager  163 . That is, the conversation function manager  165  sends a selected message group to a different mobile terminal of a specified counterpart so as to share the message group, displays newly sent and received messages after messages present in the shared message group, and stores the newly sent and received messages. Here, the conversation function manager  165  may send a message group to a counterpart mobile terminal only when the message group is not present in the counterpart mobile terminal. For example, the conversation function manager  165  may compare the user ID such as an address recorded in the message group with that of a user with whom a new conversation is to be initiated. When they are identical, the conversation function manager  165  determines whether the message group to be shared is present in the mobile terminal of the user with whom a new conversation is to be initiated. Here, a message group is assumed to have a unique identifier for identification. When a message group having an identifier identical to that of the message group to be shared is present in the mobile terminal of the user with whom a new conversation is to be initiated, the conversation function manager  165  may determine that the message group to be shared is present in the mobile terminal of the user with whom a new conversation is to be initiated, and skip transmission of the message group to be shared. When a terminal ID recorded in the message group to be shared is not identical to that of the counterpart user, or when the message group to be shared is not present in the mobile terminal of the counterpart user, the conversation function manager  165  may send the message group to be shared to the counterpart mobile terminal. The conversation function manager  165  may also send a message group to be shared to a mobile terminal of a user wishing to join the current conversation. In response to a request for a message group from a different mobile terminal, the conversation function manager  165  may send a requested message group to the different mobile terminal. To achieve this, the conversation function manager  165  may assign a unique identifier to a message group at the creation time. Unique identifiers of message groups may be shared between users participating in the same conversation. 
     As described above, the mobile terminal  100  supporting the message-based conversation function classifies many messages generated during a conversation into message groups according to preset conditions, enabling the user to search, manage and display the message groups with ease. In addition, the mobile terminal  100  may initiate a new conversation on the basis of already existing message groups. 
       FIG. 3  is a flowchart of a conversation operation method according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , the control unit  160  controls the supply of power to the components of the mobile terminal  100  at step  301 . With the supply of power, the mobile terminal  100  enters into a ready state. 
     The control unit  160  determines whether an input signal for the conversation function is generated at step  303 . When the generated input signal is not for the conversation function, the control unit  160  performs an operation indicated by the input signal at step  305 . For example, the control unit  160  may perform call handling, broadcast reception, file playback, file search, audio sound generation, game application execution, and the like. 
     When an input signal for the conversation function is generated, the control unit  160  determines whether a conversation record related to the input signal is present at step  307 . Here, the input signal for the conversation function may correspond to activation of the conversation function application  151  or to reception of a message related to a conversation. When messages are exchanged during a conversation, the control unit  160  may collect a counterpart user ID, conversation ID and terminal address from the messages as conversation records. Hence, when a counterpart user is given, the control unit  160  may determine whether a conversation record related to the counterpart user is present. To achieve this, the mobile terminal  100  stores messages exchanged during a conversation by default, and stores the counterpart user ID, conversation ID and terminal address as index information. In this case, the presence of a conversation record related to a counterpart user may be determined when the user selects a counterpart user ID, conversation ID or terminal address. 
     When a conversation record is present, the control unit  160  determines whether sharing of a previous message or message group is necessary at step  309 . When sharing of a previous message or message group is necessary, the control unit  160  sends a message or message group to be shared to a counterpart mobile terminal at step  311 . That is, as described before, when a message or message group to be shared is not present in a counterpart mobile terminal, the control unit  160  transmits the message or message group to be shared to the counterpart mobile terminal. 
     When sharing of a previous message or message group is not necessary, the control unit  160  uses an existing dialog window to display new messages at step  313 . That is, when the previous message or message group is already distributed among participants or is not needed, the control unit  160  displays a new message immediately after the previous message in an existing dialog window. 
     When a conversation record is not present (for example, conversation with a new counterpart or new conversation with an existing counterpart), the control unit  160  generates a new dialog window and conducts a conversation operation using the new dialog window at step  315 . That is, the control unit  160  displays a message received through the communication unit  110  on the display panel  141 , stores the received message in the storage unit  150 , and sends a written message to the counterpart mobile terminal. 
     The control unit  160  determines whether a message grouping condition is satisfied during the conversation at step  317 . Here, a message grouping condition may be satisfied, for example, when a preset time expires without message exchange in the current conversation or when a termination request for the current conversation is issued. Message grouping conditions may be automatically or manually triggered by various events. 
     Automatic message grouping conditions may correspond to expiration of a preset time without message exchange in a conversation, a change of the date during a conversation, generation of an input signal for terminating the conversation, expiration of a preset period or exchange of a preset number of messages during a conversation, and a preset number of appearances of words or phrases such as “bye”, “end”, “termination”, and the like in a conversation. Two or more of such message grouping conditions may be simultaneously triggered. In message grouping conditions, specific time duration, number, amount, date, phrase, or the like may be adjusted by the user. Manual message grouping conditions may correspond to an input signal for a message grouping request and an input signal for grouping a set of selected messages. 
     When a message grouping condition is satisfied, the control unit  160  classifies exchanged messages into message groups and sets display options at step  319 . Here, the message groups are stored in the conversation information database  153 . The control unit  160  may create display items corresponding to the message groups and display the display items on the display panel  141 . 
     Thereafter, the control unit  160  determines whether an input signal for ending the conversation is input at step  321 . When an input signal for ending the conversation is not input, the control unit  160  returns to step  315  or step  313  depending upon use of the new or existing dialog window. 
     As described above, the exemplary message-based conversation operation method may generate message groups on the basis of messages exchanged during a conversation. The method may initiate a new conversation using an existing message or message group. 
       FIG. 4  illustrates screen representations of individual messages and message groups in conversations according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , in response to an input signal for activating the conversation function application  151 , the mobile terminal  100  may display a conversation history screen as shown by screen  401 . To be more specific, when an input signal for selecting the conversation function application  151  is generated or a message for a conversation is received, the mobile terminal  100  activates the conversation function application  151 . Here, the mobile terminal  100  determines whether a conversation record is present on the basis of a terminal address of a counterpart user selected by the user or a terminal address contained in a received message. When a conversation record is present, the mobile terminal  100  displays a dialog window containing a conversation history on the display unit  140  as shown by screen  401 . Here, display items  41  (of quick view type) corresponding to message groups need not be displayed by default but may be displayed on the display unit  140  according to user selection (for example, scroll event). A display item  41  of quick view type may show portions of messages contained in the corresponding message group within a preset region. 
     As shown by screen  403 , a message group may be output as a display item  42  of icon type. A display item  42  of icon type does not show messages contained in the corresponding message group. A display item  42  of icon type may show the creation date of the corresponding message group or specific information such as tag information given to the corresponding message group. 
     An input signal may cause a transition between screen  403  and screen  401 . That is, when the user generates a specific event in a state where screen  401  is output, the control unit  160  may change display items  41  of quick view type into display items  42  of icon type. When the user generates a specific event in a state in which screen  403  is output, the control unit  160  may change display items  42  of icon type into display items  41  of quick view type. As described before, display items  40  need not be displayed by default, and may be displayed on the display unit  140  only when a specific event, such as scrolling, is generated. Among display items  40 , those display items  40  corresponding to recently created message groups may be displayed together with ungrouped messages. Here, messages  50  arranged below display items  40  corresponding to message groups may be ungrouped (or unclassified). That is, some messages may be ungrouped when a manual message grouping condition is configured, when an automatic message grouping condition is not satisfied, or when a special user request is issued. Display items  40  and messages  50  may be alternately placed when they are arranged in order of time. 
       FIG. 5  illustrates screen representations for an ongoing conversation with manipulation of message groups according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , in response to an input signal for the conversation function, the control unit  160  of the mobile terminal  100  executes the conversation function application  151  and displays a corresponding application screen as shown by screen  501 . Here, the control unit  160  determines whether a conversation record is present on the basis of a counterpart user selected by the user, conversation identifier or a counterpart terminal address. When a conversation record is present, the control unit  160  displays previous messages  50  on the display unit  140  as shown by screen  501 . When a pertinent conversation record is not present, the control unit  160  outputs a new dialog window and displays exchanged messages  50  in the new dialog window as shown by screen  501 . 
     When the user may generate a scroll event to find a message group related to the current counterpart user, the control unit  160  outputs display items  42  of icon type corresponding to hidden message groups on the display unit  140  as shown by screen  503 . Other gesture-related events may also be used to find a message group. For example, when the user makes a long press on a specific portion of screen  501 , display items  42  of icon type may be output on the current screen as shown by screen  503 . When all message groups related to a given counterpart mobile terminal are already output as display items  42  of icon type, the control unit  160  may ignore an additional scroll event by keeping display status constant. Here, the control unit  160  may output an alert phrase “no more message groups”. 
     In a state in which one or more display items  42  of icon type are output as shown by screen  503 , the user may select one display item  42  to identify contents of a message group corresponding to the selected display item  42 . For example, when the user generates an input signal for selecting one display item  42  of icon type as shown by screen  505 , the control unit  160  may output a display item  41  of quick view type as shown by screen  507 . A display item of quick view type may show portions of messages contained in the corresponding message group within a screen region. Through a display item of quick view type, the user may easily identify contents of the corresponding message group. 
     When the user generates an event for the conversation function in the display item  41  of quick view type as shown by screen  507 , the control unit  160  may open a new dialog window in a full screen format using messages in the message group corresponding to the display item  41  as shown by screen  509  or in a small screen format using only messages currently appearing in the display item  41  of quick view type. That is, the control unit  160  may open a new dialog window of a smaller size with messages appearing in the display item  41  of quick view type or open a new dialog window of a larger size with a larger number of messages belonging to the message group corresponding to the display item  41 . 
     In response to a user request, the control unit  160  may output a message composer  60  at a region of the display unit  140  as shown by screen  511 . The control unit  160  may display a message written using the message composer  60  and a message received from the counterpart mobile terminal immediately below messages of the previous conversation as shown by screen  513 . Hence, the mobile terminal  100  may initiate a new conversation in succession to the previous conversation. 
     In the case of receiving a message from another mobile terminal as a request for initiating a new conversation in succession to a previous conversation, the control unit  160  may output the received message immediately below messages in a message group of the previous conversation. To be more specific, when a request for initiating a new conversation and message group information are received from a counterpart mobile terminal, the control unit  160  determines whether a message group of a previous conversation indicated by the received message group information is stored. When an indicated message group is stored, the control unit  160  displays messages in the indicated message group on the display unit  140  and displays newly exchanged messages immediately after the messages in the indicated message group. 
     When an indicated message group is not stored, the control unit  160  may send a request for the indicated message group to the counterpart mobile terminal automatically or according to user selection. When the indicated message group is received from the counterpart mobile terminal, the control unit  160  may store the received message group, display messages in the received message group on the display unit  140 , and display newly exchanged messages immediately after the messages in the received message group. Hence, the mobile terminal  100  may initiate a new conversation using messages of the previous conversation. 
     In one conversation, message grouping conditions may be different between counterpart mobile terminals. However, automatic message grouping conditions based on date or time may produce the same message groups for counterpart mobile terminals. Hence, to initiate a new conversation using a message group of the previous conversation, it is necessary to determine whether the message group is shared between participants. When the message group to be shared is already present, the user may control the mobile terminal  100  to skip sending a message group request. 
       FIG. 6  illustrates screen representations for splitting a message group according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , in response to a user request, the control unit  160  of the mobile terminal  100  may output one or more display items  42  of icon type corresponding to message groups on the display unit  140 . When the user selects one of the display items  42  of icon type as a quick view request, the control unit  160  may change the selected display item  42  of icon type into a display item  41  of quick view type, which shows portions of messages contained in the corresponding message group, as shown by screen  601 . As described before, in response to a quick view request, the control unit  160  may show portions of messages contained in a corresponding message group within a screen region. The control unit  160  may provide a scroll function to the display item  41  of quick view type so that all messages contained in the corresponding message group can be viewed. In the present invention, the screen region allocated to a display item  41  of quick view type may be adjusted according to situations. For example, when a large number of messages are contained in the corresponding message group, the screen region allocated to a display item  41  of quick view type may be increased, or the message display size may be reduced, so that a larger number of messages can be displayed. When the screen region allocated to a display item  41  of quick view type is not sufficient to accommodate all messages contained in the corresponding message group, the control unit  160  may provide a scroll function to the display item  41  so that all the messages can be viewed. 
     The user may issue a request for splitting a message group. For example, as shown by screen  601 , the user may enter a first touch gesture at a portion of the display item  41  of quick view type and enter a second touch gesture at another portion thereof while maintaining the first touch gesture to split the message group corresponding to the display item  41 . The control unit  160  may divide the corresponding message group on the basis of the touch gestures. For example, as shown by screen  603 , when the second touch gesture is a drag action in a direction, the control unit  160  may divide the message group with respect to the drag action. Thereafter, the control unit  160  may output two display items  41  of quick view type corresponding to the two divided message groups as shown by screen  605 . Here, the control unit  160  may recognize simultaneous occurrence of two touch gestures at different portions of a display item  41  of quick view type as activation of a message group splitting function, and identify the demarcation line between the two split message groups on the basis of the movement of the second touch gesture. Thereafter, the control unit  160  may generate two display items  41  of quick view type and associate the display items  41  respectively with the two split message groups. 
     In the above description, a message group is divided by entering multiple touch gestures and dragging. However, splitting of a message group may be performed in other ways. For example, when touch gestures for selecting one or more of the messages contained in a message group and binding the selected messages are entered, the control unit  160  may create one split message group containing the selected messages and create another split message group containing the remaining messages. Hence, the user may create a new message group by selecting messages having specific properties among messages contained in a given message group. 
     The control unit  160  may delete a display item  41  of quick view type corresponding to a message group in a state indicated by screen  605 . That is, when the user selects a display item  40  and generates an input signal for deleting the selected display item  40 , the control unit  160  may remove both the display item  40  and a message group associated with the display item  40 . 
       FIG. 7  illustrates screen representations for merging message groups according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 7 , in response to a user request, the control unit  160  may output multiple display items  40  corresponding to message groups on the display unit  140 . For example, when multiple message groups are present for a given counterpart user, in response to a request for activating the conversation function, the control unit  160  may output multiple display items  40  corresponding to the message groups on the display unit  140  as shown by screen  701 . Here, the display item  40  may be a display item  41  of quick view type or a display item  42  of icon type. According to user settings, the control unit  160  may output display items  41  of quick view type only or output a display item  41  of quick view type and a display item  42  of icon type in combination. 
     The user enters a touch gesture for selecting a display item  41  corresponding to a first message group to be merged as shown by screen  701 . For example, when the user enters a long press gesture on the display unit  140  outputting display items  41  corresponding to message groups, the control unit  160  may recognize the gesture as a request for merging message groups. Here, the control unit  160  may highlight the selected message group or apply layering effects thereto so that the selected message group may be readily noticeable. 
     The user enters a touch gesture for selecting a display item  41  corresponding to a second message group to be merged as shown by screen  703 . Here, the user may maintain the touch gesture selecting the first message group to be merged. When two display items are selected as shown by screen  703  or the two touch gestures are drawn closer together, the control unit  160  may merge the two message groups associated with the selected display items. Here, the control unit  160  may create a merger message group containing messages of the selected message groups in sequence. Thereafter, the control unit  160  may output a display item  41  of quick view type corresponding to the merger message group on the display unit  140  as shown by screen  705 . 
     The user may merge more than two message groups. For example, the user may enter a long press gesture on a display item  41  associated with a first message group, and select display items  41  associated with message groups in sequence while maintaining the long press gesture. Then, the control unit  160  may merge the message groups by adding messages of the message groups selected in sequence to the first message group (the merger message group). Here, the messages in the merger message group may be arranged in order of selection of the merged message groups. 
     The user may restrict the size of a display item  41  associated with the merger message group on the display unit  140  to allow other display items  41  to be adequately output on the display unit  140 . This enables selection of a display item  41  not associated with the merger message group without a scroll action. The control unit  160  may resize characters and images of the merger message group so that message contents of the merger message group can be displayed as much as possible in a restricted region. 
     The display item that is selected first for merging message groups may be a display item  41  of quick view type or a display item  42  of icon type. That is, the display item corresponding to the merger message group may be a display item  41  of quick view type or a display item  42  of icon type. 
     When a display item  41  of quick view type and a display item  42  of icon type are selected for merge operation, the control unit  160  may merge the corresponding message groups and output a display item  41  of quick view type together with some portion of information carried by the display item  42  of icon type, or the control unit  160  may merge the corresponding message groups and output a new display item  42  of icon type on the display unit  140 . 
     When two display items  42  of icon type are selected for merge operation, the control unit  160  may merge the corresponding message groups, output a new display item  42  of icon type or leave only one of the two display items  42  of icon type, and output a display item  41  of quick view type after merging. That is, when two display items  42  of icon type are selected for merge operation, the control unit  160  may merge the corresponding message groups, remove the display items  42  of icon type from the display unit  140 , and output a display item  41  of quick view type corresponding to the merger message group. 
       FIG. 8  illustrates screen representations for moving a message group according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 8 , in response to a user request, the control unit  160  may output one or more display items  42  of icon type corresponding to message groups on the display unit  140  as shown by screen  801 . That is, in response to a user request after outputting a dialog window containing messages on the display unit  140 , the control unit  160  may output display items  42  of icon type corresponding to message groups on the display unit  140 . Here, the control unit  160  may also output a message  50  after the display items  42  according to availability of a display region. That is, the control unit  160  may place the display items  42  of icon type between existing messages  50  without allocating a separate page. To move a specific message group on the display unit  140 , the user may enter a long press touch gesture to select a display item  42  of icon type associated with the message group to be moved. 
     Then, the control unit  160  may provide a visual effect to the selected display item  42  of icon type to indicate a selection for movement. For example, the control unit  160  may highlight the boundary of the selected display item  42  or impart layering effects thereto. 
     The user moves the selected display item  42  of icon type to a desired position by dragging and releasing the touch gesture as shown by screen  803 . Then, the control unit  160  may change positions of display items  41  during movement of the selected display item  42  and place the selected display item  42  at a position where the touch gesture is released on the display unit  140 . Such movement of a message group may also be performed between individual messages  50 . For example, when a selected display item  42  of icon type is dragged below a message  50  on the display unit  140 , the control unit  160  may place the selected display item  42  of icon type below the message  50 . Here, the control unit  160  may move a second message  50 , which is placed at the position to which the selected display item  42  is moved, to a nearby or preset position. 
       FIG. 9  illustrates screen representations for sorting message groups according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 9 , in response to a user request, the control unit  160  may output one or more display items  42  of icon type on the display unit  140  as shown by screen  901 . That is, in response to a user request after outputting a dialog window containing messages on the display unit  140 , the control unit  160  may output display items  42  of icon type corresponding to message groups on the display unit  140 . More particularly, the control unit  160  may attach a priority indication to each display item  42  of icon type. To achieve this, the control unit  160  may provide a menu item for enabling the user to attach a priority indication to the corresponding display item  42  of icon type. For example, the control unit  160  may output a check option like an asterisk to each display item  42  of icon type as shown by screen  901 . Then, the user may set the check option of a display item  42  of icon type to thereby assign a priority indication to a message group corresponding to the display item  42 . 
     When the check option of a display item  42  of icon type is set, the control unit  160  may assign a priority indication to a message group corresponding to the display item  42  and update the message group information stored in the conversation information database  153 . In addition, the control unit  160  may move the display item  42  of icon type whose check option is set to a position close to the most recent message, so that the user can readily identify the message group corresponding to the display item  42  as shown by screen  903 . Hence, the user may view display items  42  of icon type corresponding to important message groups first by entering a scroll gesture on the current screen. 
     The control unit  160  may treat a newly created display item  42  of icon type as important by placing the newly created display item  42  at a position close to the most recent message  50 . However, a display item  42  of icon type whose check option is set may be placed at a position closer to the most recent message  50  than a newly created display item  42  of icon type. 
     In  FIGS. 8 and 9 , movement and sorting of display items are described using display items  42  of icon type. However, the same description may be applied to display items  41  of quick view type. That is, on the display unit  140 , a display item  41  of quick view type may be selected and moved to another position, or may be given a priority indication for sorting. For priority assignment, a check option may be attached to a portion of each display item  41  of quick view type. 
       FIG. 10  illustrates screen representations for searching or browsing message groups according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 10 , in response to a user request, the control unit  160  may output one or more display items  42  of icon type corresponding to message groups on the display unit  140  as shown by screen  1001 . That is, in response to a user request like a scroll event after outputting a dialog window containing messages  50  on the display unit  140 , the control unit  160  may output display items  42  of icon type on the display unit  140 . When the user enters a touch gesture on one of the display items  42  of icon type as shown by screen  1001 , the control unit  160  may change the touched display item  42  of icon type into a display item  41  of quick view type, which shows portions of messages contained in the corresponding message group within a preset region, as shown by screen  1003 . 
     For example, when a tap event occurs at a display item  42  of icon type in screen  1001 , the control unit  160  may change the tapped display item  42  of icon type into a display item  41  of quick view type as shown by screen  1003 . The display item  41  of quick view type shows portions of messages contained in the corresponding message group within a preset region. In this process, the control unit  160  may rearrange display items on the display unit  140  to allocate a wider display region to the display item  41  of quick view type. For example, the control unit  160  may shift the untapped display items  42  of icon type away from the tapped display item  42  of icon type to be changed on the display unit  140 . 
     When the user enters a touch gesture on the display item  41  of quick view type as shown by screen  1003 , the control unit  160  may enlarge the display item  41  of quick view type in a full screen format as shown by screen  1005 . That is, the control unit  160  displays messages  50  contained in a message group corresponding to the touched display item  41  of quick view type on the full screen of the display unit  140 . 
     In the above description, output of a display item of quick view type and full screen display of a message group are performed in sequence. However, the present invention is not limited thereto. For example, as shown by screen  1007  and screen  1009 , when a particular event occurs at a display item  42  of icon type, the control unit  160  may directly display messages contained in a message group corresponding to the display item  42  of icon type in a full screen format without outputting a display item  41  of quick view type. That is, when the user generates a preset event such as a pinch-zoom event on one of multiple display items  42  of icon type as shown by screen  1007 , the control unit  160  may output messages contained in a message group corresponding to the selected display item  42  of icon type in a full screen format as shown by screen  1009 . 
     In addition, the control unit  160  may return from the full screen (screen  1005  or screen  1009 ) to the original screen (screen  1001  or screen  1007 ) differently depending upon touch gestures. For example, when a touch event like tap for the previous screen occurs at screen  1005 , the control unit  160  may restore screen  1003 . When a touch event like pinch-zoom for the original screen occurs at screen  1009  (or screen  1005 ), the control unit  160  may directly restore screen  1007  (or screen  1001 ). 
       FIG. 11  illustrates a display item of icon type in a first form for depicting message group information according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 11 , a message group may be represented by a display item  42  of icon type with a given size, which can be output on the display unit  140 . The display item  42  of icon type may include a time region  401 , a priority region  402 , a subject region  403 , a tag region  404 , and a margin region  407 . 
     The time region  401  is used to record a time duration during which messages in the message group are exchanged. The control unit  160  examines date and time values of exchanged messages when a message group containing the messages is created as a result of message grouping, and records the identified time duration in the time region  401  of the corresponding display item  42  of icon type. 
     The priority region  402  is used to record a priority value assigned to the message group. The priority value recorded in the priority region  402  may be changed by the user. The control unit  160  may change the priority of the corresponding message group in response to a touch event occurring in the priority region  402 . Here, the priority of a message group may be given in two or more levels. The priority region  402  may be displayed differently in shape, image, icon, text, color or brightness according to priority level. 
     The subject region  403  is used to record information describing the messages in the message group. Such descriptive information should be readily understandable to the user. To describe the message, the control unit  160  may automatically extract a portion of the longest message in the message group and write the extracted message portion to the subject region  403 . Alternatively, the control unit  160  may automatically extract a portion of a message that contains the largest number of words frequently used in the messages of the message group and write the extracted message portion to the subject region  403 . Such an automatic approach may extract portions of messages in the message group according to preconfigured settings or synthesize a short sentence summarizing messages in the message group using a contextual analysis technique. Here, the mobile terminal  100  may store an algorithm and database supporting discourse analysis or connect to a server providing a discourse analysis service. Alternatively, the user may directly write desired information to the subject region  403 . To achieve this, when the message group is created, the control unit  160  may provide a window enabling the user to enter information to be written to the subject region  403 . Furthermore, the control unit  160  may insert a value indicating the number of messages in the message group into the subject region  403  for better understanding of the message group. 
     The tag region  404  is used to provide tag information composed of meaningful words frequently used in the messages of the message group. The control unit  160  may analyze messages of the message group to extract frequently occurring meaningful words, and record the extracted meaningful words in order of occurrences in the tag region  404 . Here, the most frequently used word is listed as a tag at the top portion of the tag region  404 . The control unit  160  may record only words whose number of occurrences exceeds a threshold value as tags in the tag region  404 . 
     The margin region  407  may be a region excluding the time region  401 , priority region  402 , subject region  403 , and tag region  404 . The margin region  407  may be divided into a background region  405  and a side region  406 . The background region  405  is used to represent various colors and textural properties according to importance of the message group or user settings. The color of the background region  405  may be changed according to the importance or priority of the message group in terms of the number of views or searches. The mapping between colors and importance levels may be configured by the designer in advance or by the user. 
     The side region  406  may have a thickness indicating the number of messages in the message group. The layers at the side region  406  may indicate the number of stacked message groups in a conversation. When messages in a conversation are classified by a message grouping condition into message groups, the message groups may have different sizes. Hence, when a message group contains a small number of messages, the side region  406  is thin. And, when a message group contains a large number of messages, the side region  406  is thick. That is, the thickness of the side region  406  may vary depending upon the number of messages in the corresponding message group. 
     Display items  42  of icon type may be individually displayed on the display unit  140 . However, when there are a large number of message groups in a conversation, the display region of the display unit  140  may be insufficient to individually present display items  42  of icon type. In this case, as shown in  FIG. 11 , multiple display items  42  of icon type may be stacked on the display unit  140 , and the side region  406  may indicate this. By entering a touch gesture like a flick on a display item  42  of icon type, the user may view another display item  42  of icon type placed below the touched display item  42 . 
     The margin region  407  may include an earmark region  408  at a corner. The earmark region  408  may indicate that another display item is present below the current display item  42  of icon type and the current display item  42  may be turned over. By entering a touch gesture on the earmark region  408 , the user may hide the current display item  42  of icon type from the screen and view another display item  42  of icon type. Here, the hidden display item  42  of icon type may be placed at the bottom of the stacked display items  42 . 
     The earmark region  408  formed at a corner may be used to browse messages contained in the message group corresponding to the current display item  42  of icon type. That is, when the user invokes a page turning function by entering a touch gesture on the earmark region  408 , the control unit  160  may output a quick view screen of a page containing a number of messages in the corresponding message group. To view the remaining messages of the message group, the user may enter a touch gesture on the earmark region  408  in succession. For example, it may be assumed that a message group is composed of the following messages. 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 Speaker 
                   
               
               
                 Sequence 
                 (sender) 
                 Message 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 A 
                 Hi 
               
               
                 2 
                 B 
                 Hi 
               
               
                 3 
                 A 
                 How are you? 
               
               
                 4 
                 B 
                 I&#39;m fine, thanks. 
               
               
                 5 
                 A 
                 I&#39;m getting married soon. 
               
               
                 6 
                 B 
                 Congratulations! 
               
               
                 7 
                 A 
                 Shall we meet for dinner before the wedding day? 
               
               
                 8 
                 B 
                 Ok. When? 
               
               
                 9 
                 A 
                 The day after tomorrow at 6:30 PM. 
               
               
                 10 
                 B 
                 All right. See you then. 
               
               
                   
               
            
           
         
       
     
     Whenever the user invokes a page turning function in the display item  42  of icon type, a quick view screen of a page containing, for example, the next three messages may be output on the display unit  140 . That is, four pages (first page containing the first to third messages, second page containing the fourth to sixth messages, third page containing the seventh to ninth messages, and fourth page containing the tenth message) may be displayed in sequence as a quick view screen. 
       FIG. 12  illustrates a display item of quick view type in a first form for depicting message group information according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 12 , in the mobile terminal  100 , a message group may be represented by a display item  41  of quick view type. The display item  41  of quick view type includes a view region  410  in which a number of messages  50  contained in the message group are output. The layers at the side region  406  may indicate the number of stacked message groups in a conversation. The size of the view region  410  may be set in advance, and may be adjusted by the user. For example, the user may increase the size of the view region  410  by entering a touch gesture for expansion at an edge of the view region  410 . When the size of the view region  410  is changed, the control unit  160  may adjust the number or display size of messages to be output. 
     Display items  42  of icon type ( FIG. 11 ) and display items  41  of quick view type ( FIG. 12 ) may be output together on the display unit  140 . That is, some message groups in a conversation may be presented as display items  42  of icon type, and other message groups may be presented as display items  41  of quick view type. A display item may toggle between quick view type and icon type according to user selection. The mobile terminal  100  may output either display items  42  of icon type or display items  41  of quick view type by default, and may change default settings according to user selection. 
     To present a large number of message groups, display items  41  of quick view type may be stacked on the display unit  140 . To view or browse stacked message groups, the display item  41  of quick view type may include an earmark region  408  at a corner. Use of the earmark region  408  for browsing stacked message groups is described later in connection with  FIGS. 13 and 14 . 
       FIG. 13  illustrates screen representations for searching or browsing display items of quick view type according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 13 , the control unit  160  may output a display item  41  of quick view type showing a number of messages contained in the message group. The display item  41  of quick view type may include a view region  410  and a side region  406 . The view region  410  is used to output a number of messages. The side region  406  is used to indicate the number of message groups, and the thickness thereof is varied according to the number of message groups. As shown by screen  1301 , to present multiple message groups, display items  41  of quick view type may be stacked on the display unit  140 . To enable the user to search or browse stacked display items  41  of quick view type corresponding to multiple message groups, each display item  41  of quick view includes an earmark region  408  at a corner. 
     When display items  41  of quick view type are stacked on the display unit  140  as shown by screen  1301 , the user may enter a touch gesture on a portion of the side region  406  to view another display item  41  of quick view type placed below the touched display item  41  of quick view type. That is, the user may enter a touch gesture like a drag or a flick on the earmark region  408  to turn over the topmost display item  411  of quick view type. 
     Then, the control unit  160  may turn over the topmost display item  411  of quick view type in a direction of the touch gesture, and output another display item  412  of quick view type placed below the topmost display item  411  of quick view type as shown by screen  1303 . Here, the turn-over speed of the topmost display item  411  of quick view type may be varied according to the movement speed and distance of the touch gesture. When the earmark region  408  of the topmost display item  411  of quick view type is moved more than a threshold distance, the control unit  160  may hide the topmost display item  411  of quick view type from the screen and output the next display item  412  of quick view type in full size. Here, the hidden display item  411  of quick view type may be placed at the bottom of the stacked display items  41 . 
     Similarly, when the user touches some layers of the side region  406  and moves the side region  406  in a direction, the control unit  160  may move a corresponding number of display items  41  of quick view type in the direction of the touch gesture while bending the same and gradually output a display item  412  of quick view type placed below the moved display items  41 . When the touch gesture is released, the control unit  160  may move the moved display items  41  of quick view type back to the original position on the display unit  140 . 
       FIG. 14  illustrates additional screen representations for searching or browsing display items of quick view type according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 14 , the control unit  160  may output a display item  41  of quick view type showing a number of messages contained in the message group as shown by screen  1401 . The display item  41  of quick view type may include a view region  410  and a side region  406 . The view region  410  is used to output a number of messages. The side region  406  is used to indicate a number of stacked message groups. The view region  410  includes an earmark region  408  at a corner. When the earmark region  408  is folded, this indicates the presence of another display item below the current display item. When the earmark region  408  is not folded, this indicates the absence of another display item below the current display item. 
     To rapidly browse the message groups, the user may enter a touch gesture at the side region  406  on the right as shown by screen  1401 . The control unit  160  may recognize this touch gesture as a touch event for rapid browsing of the message groups. 
     When the user enters a drag gesture while touching the side region  406 , the control unit  160  may move the side region  406  in a direction of the drag gesture while bending the touched display items  41  as shown by screen  1403 . Here, the number of bent or moved display items  41  of quick view type may correspond to the number of touched layers of the side region  406  or to the touched thickness thereof. When the side region  406  is moved more than a threshold distance (for example, one third of the view region length), the control unit  160  may turn one or more of the bent display items  41  back to the original position (similar to page turning effects) as shown by screen  1405 . Here, among the bent display items  41  of quick view type, the control unit  160  may turn over a display item  41  of quick view type that is released from the touch gesture (i.e., a display item having escaped from the area of the touch gesture) back to the original position. Hence, the user may slowly or rapidly browse the message groups by adjusting the speed of a touch and drag action on the display items  41  of quick view type. 
     In the above description, searching or browsing of message groups is performed using display items of quick view type. However, the present invention is not limited thereto. That is, searching or browsing of message groups may also be performed using display items of icon type. In other words, the description provided in relation to  FIGS. 13 and 14  is applicable to the case of  FIG. 11 . 
       FIG. 15  illustrates a display item of icon type in a second form for depicting message group information according to an exemplary embodiment of the present invention.  FIG. 16  illustrates a display item of quick view type in a second form for depicting message group information according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 15 , the display item  42  of icon type corresponding to a message group includes a background region  405  and rolled-up regions  409 . The background region  405  is the same as that shown in  FIG. 11 , and a description thereof is omitted. 
     The display item  42  of icon type may have an upper rolled-up region  409  at the upper boundary and a lower rolled-up region  409  at the lower boundary. Here, the upper rolled-up region  409  is rolled inwards, and the lower rolled-up region  409  is rolled outwards. The two rolled-up regions  409  may be rolled in the same direction. 
     The amount of rolling up of the rolled-up region  409  may indicate the number of messages in the corresponding message group. That is, when the corresponding message group contains a large number of messages, the rolled-up region  409  of the display item  42  of icon type may be rolled up many times or the display item  42  may become thick. Hence, the user may estimate the number of messages in the message group on the basis of the amount of rolling up of the rolled-up region  409 . 
     Referring to  FIG. 16 , the display item  41  of quick view type representing a message group may include a view region  410  and a rolled-up region  409  at the boundary. The view region  410  is used to output a number of messages. As described before in relation to  FIG. 15 , the amount of rolling up of the rolled-up region  409  or the thickness thereof may indicate the number of messages in the corresponding message group. 
     When a scroll event occurs in the view region  410  of the display item  41  of quick view type, the control unit  160  may scroll messages up or down and roll the rolled-up region  409  in a direction. For example, when the user enters a scroll-up gesture on the view region  410 , the control unit  160  may roll the rolled-up region  409  inwards and rearrange the messages accordingly. When a preset touch event occurs at the display item  41  of quick view type, the control unit  160  may display the display item  41  in a full screen format. In this case, the rolled-up region  409  may be hidden from the screen. 
     As described hereinabove, an exemplary message-based conversation operation method of the present invention enables the user to classify conversational messages into groups according to preset conditions and manipulate the message groups. Hence, the user can easily find a desired message and perform message management in a more convenient manner. 
     If necessary, the mobile terminal  100  may further include various components. That is, although not shown, the mobile terminal  100  may further include a short-range communication module for short-range communication, a data communication interface based on wired and wireless communication, an Internet communication module for Internet access, a digital broadcast receiving module for playing digital broadcasts, and the like. With the digital convergence trend, it should be apparent to those skilled in the art that the mobile terminal  100  may further include a unit comparable to the above-described units, and one unit of the mobile terminal  100  may be removed or replaced with another unit. 
     The exemplary mobile terminal  100  may be a device capable of providing a menu page and base pages at the same level, and may be any information and communication appliance or multimedia appliance, such as a mobile communication terminal based on communication protocols supporting various communication systems, a Portable Multimedia Player (PMP), a digital broadcast receiver, a Personal Digital Assistant (PDA), a music player like an MP3 player, a portable game console, a smartphone, a laptop computer, a handheld computer, and the like. 
     In an exemplary implementation, the message-based conversation operation method enables a mobile terminal to classify a large number of messages sent and received during conversations into groups automatically according to preset conditions or user selection. Hence, it is possible to easily find a desired one of the classified messages, and to use the found message to compose a new message or to initiate a new conversation. In addition, as the message groups are presented in an efficient and intuitive way, the user may easily perform message search and manipulation. 
     While the present has been described and shown in detail with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.