Abstract:
An information processing apparatus includes an output unit for outputting information. A first recording unit records first information for causing the output unit to output predetermined information. An analysis unit analyzes the first information. A determination unit determines whether to obtain second information, which is referenced by the first information, in accordance with the analysis result. An obtaining unit obtains the second information in accordance with the determination result. A second recording unit records the second information. A generation unit generates third information, which is output from the output unit, in accordance with the analysis result. The first information includes fourth information indicating a condition for obtaining the second information. The determination unit determines whether the condition is satisfied on the basis of the fourth information. The obtaining unit obtains the second information when the condition is satisfied.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to information processing apparatuses, information processing methods, recording media, and programs, and more particularly relates to an information processing apparatus, an information processing method, a recording medium, and a program suitable for use in reading electronic books (hereinafter referred to as e-books).  
           [0003]    2. Description of the Related Art  
           [0004]    Hitherto, publishing has been done using paper as a primary medium, such as books, newspaper, and magazines. Recently, publishing using media other than paper, namely, electronic publishing (hereinafter referred to as e-publishing), has become widespread as computers have advanced, the use thereof has been expanded, and the network infrastructure has been developed.  
           [0005]    In electronic publications (hereinafter referred to as e-publications) or in e-books, books that used to be printed on paper and published are digitized. Digital data includes text, images, audio data, and video data. A user can download an e-book from a predetermined web server through the Internet and store the downloaded e-book in a predetermined storage medium, a personal computer, or a predetermined player. Alternatively, the user can purchase, for example, a CD-ROM (Compact Disk Read Only Memory) that has recorded therein beforehand an e-book, thus allowing the user to read the e-book. The user can use a PC or a predetermined player in which e-book data is recorded or a recording medium having e-book data recorded therein is loaded to play the e-book.  
           [0006]    In e-books, a link is placed at a predetermined word. When the user selects the link, the display screen jumps to a related portion of the same file, or alternatively, another file for another related book is opened and displayed on the display screen.  
           [0007]    In e-books downloaded through the Internet or distributed using recording media, when a revised version is put on sale, the entire data for the revised version needs to be downloaded or a recording medium having the revised version recorded therein needs to be purchased.  
           [0008]    Although technology has been developed to display predetermined data for another file when a link included in a file is selected, thus allowing a user to reference a plurality of related books, no technology has been developed to simultaneously display all pieces of related information on one page.  
           [0009]    In other words, technology related to e-publication is based on replacing the paper medium by the electronic medium, in which searching and linking technology is used. Therefore, although e-publication uses digital data, the advantages of digital data are not fully utilized.  
         SUMMARY OF THE INVENTION  
         [0010]    In view of the foregoing circumstances, it is an object of the present invention to provide an e-book which effectively utilizes the characteristics of digital data.  
           [0011]    An information processing apparatus of the present invention includes an output unit for outputting information; a first recording unit for recording first information for causing the output unit to output predetermined information; an analysis unit for analyzing the first information, which is recorded by the first recording unit; a determination unit for determining whether or not to obtain second information, which is referenced by the first information, in accordance with the analysis result by the analysis unit; an obtaining unit for obtaining the second information in accordance with the determination result by the determination unit; a second recording unit for recording the second information, which is obtained by the obtaining unit; and a generation unit for generating third information, which is output from the output unit, in accordance with the analysis result by the analysis unit. The first information includes fourth information indicating a condition for obtaining the second information by the obtaining unit. The determination unit determines whether or not the condition for obtaining the second information is satisfied on the basis of the fourth information. The obtaining unit obtains the second information when it is determined by the determination unit that the condition for obtaining the second information is satisfied.  
           [0012]    The fourth information may include any one of conditions relating to date, period, and position.  
           [0013]    The first information may further include fifth information relating to obtaining the second information. When the fifth information includes a storage location of the second information and when the storage location stores a plurality of pieces of second information, the generation unit may generate the third information to include the plurality of pieces of second information, which are switched and output at predetermined intervals.  
           [0014]    The second recording unit may set a unique filename for each one of the plurality of pieces of second information and may record the second information.  
           [0015]    An information processing method of the present invention includes an output control step of controlling outputting information; a first recording control step of controlling recording first information for controlling outputting predetermined information in the output control step; an analysis step of analyzing the first information, the recording thereof being controlled in the first recording control step; a determination step of determining whether or not to obtain second information, which is referenced by the first information, in accordance with the analysis result obtained in the analysis step; an obtaining step of obtaining the second information in accordance with the determination result obtained in the determination step; a second recording control step of controlling recording the second information, which is obtained in the obtaining step; and a generation step of generating third information, the outputting thereof being controlled in the output control step, in accordance with the analysis result obtained in the analysis step. The first information includes fourth information indicating a condition for obtaining the second information in the obtaining step. It is determined in the determination step whether or not the condition for obtaining the second information is satisfied on the basis of the fourth information. When it is determined in the determination step that the condition for obtaining the second information is satisfied, the second information is obtained in the obtaining step.  
           [0016]    A program recorded in a recording medium of the present invention includes an output control step of controlling outputting information; a first recording control step of controlling recording first information for controlling outputting predetermined information in the output control step; an analysis step of analyzing the first information, the recording thereof being controlled in the first recording control step; a determination step of determining whether or not to obtain second information, which is referenced by the first information, in accordance with the analysis result obtained in the analysis step; an obtaining step of obtaining the second information in accordance with the determination result obtained in the determination step; a second recording control step of controlling recording the second information, which is obtained in the obtaining step; and a generation step of generating third information, the outputting thereof being controlled in the output control step, in accordance with the analysis result obtained in the analysis step. The first information includes fourth information indicating a condition for obtaining the second information in the obtaining step. It is determined in the determination step whether or not the condition for obtaining the second information is satisfied on the basis of the fourth information. When it is determined in the determination step that the condition for obtaining the second information is satisfied, the second information is obtained in the obtaining step.  
           [0017]    A program of the present invention includes an output control step of controlling outputting information; a first recording control step of controlling recording first information for controlling outputting predetermined information in the output control step; an analysis step of analyzing the first information, the recording thereof being controlled in the first recording control step; a determination step of determining whether or not to obtain second information, which is referenced by the first information, in accordance with the analysis result obtained in the analysis step; an obtaining step of obtaining the second information in accordance with the determination result obtained in the determination step; a second recording control step of controlling recording the second information, which is obtained in the obtaining step; and a generation step of generating third information, the outputting thereof being controlled in the output control step, in accordance with the analysis result obtained in the analysis step. The first information includes fourth information indicating a condition for obtaining the second information in the obtaining step. It is determined in the determination step whether or not the condition for obtaining the second information is satisfied on the basis of the fourth information. When it is determined in the determination step that the condition for obtaining the second information is satisfied, the second information is obtained in the obtaining step.  
           [0018]    According to an information processing apparatus, an information processing method, and a program of the present invention, first information for outputting predetermined information is recorded. The recorded first information is analyzed. It is determined whether or not to obtain second information, which is referenced by the first information, in accordance with the analysis result. The second information is obtained in accordance with the determination result. The obtained second information is recorded. Third information to be output is generated in accordance with the analysis result. The first information includes fourth information indicating a condition for obtaining the second information. It is determined whether or not the condition for obtaining the second information is satisfied on the basis of the fourth information. The second information is obtained when it is determined that the condition for obtaining the second information is satisfied. Accordingly, a condition for obtaining information can be set in detail, and an e-book of high added value can be provided. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 illustrates an e-book providing system to which the present invention is applied;  
         [0020]    [0020]FIG. 2 is a block diagram showing the configuration of a personal computer shown in FIG. 1;  
         [0021]    [0021]FIG. 3 is a block diagram showing the configuration of an e-book player shown in FIG. 1;  
         [0022]    [0022]FIG. 4 is a block diagram showing the configuration of a personal digital assistant (PDA);  
         [0023]    [0023]FIG. 5 is a functional block diagram for performing processing to display a content file;  
         [0024]    [0024]FIG. 6 is a flowchart showing a content-file displaying process;  
         [0025]    [0025]FIG. 7 is an illustration of tags;  
         [0026]    [0026]FIG. 8 is another illustration of tags;  
         [0027]    [0027]FIG. 9 is another illustration of tags;  
         [0028]    [0028]FIG. 10 is a flowchart showing a resource-file accessing process:  
         [0029]    [0029]FIG. 11 is an illustration of a guidebook provided as an e-book to which the present invention is applied;  
         [0030]    [0030]FIG. 12 is an illustration of a source included in a content file;  
         [0031]    [0031]FIG. 13 is another illustration of a source included in a content file;  
         [0032]    [0032]FIG. 14 is another illustration of a source included in a content file;  
         [0033]    [0033]FIG. 15 illustrates a case in which a plurality of pieces of image data is referenced;  
         [0034]    [0034]FIG. 16 is a flowchart showing a specified-file reference process;  
         [0035]    [0035]FIG. 17 is an illustration of a source included in a content file;  
         [0036]    [0036]FIG. 18 is another illustration of a source included in a content file;  
         [0037]    [0037]FIG. 19 illustrates an e-book display screen displaying a reference portion;  
         [0038]    [0038]FIG. 20 is an illustration of a source included in a content file;  
         [0039]    [0039]FIG. 21 illustrates the e-book display screen displaying an icon;  
         [0040]    [0040]FIG. 22 illustrates the e-book display screen when there is no content to be referenced;  
         [0041]    [0041]FIG. 23 is a flowchart showing a jumping process of jumping to the top page;  
         [0042]    [0042]FIG. 24 illustrates a specific example of the jumping process of jumping to the top page;  
         [0043]    [0043]FIG. 25 is a flowchart showing a process of displaying a specified reference portion;  
         [0044]    [0044]FIG. 26 illustrates the e-book display screen in which another window displays a reference portion;  
         [0045]    [0045]FIG. 27 illustrates a reference book and a glossary to which the present invention is applied;  
         [0046]    [0046]FIG. 28 illustrates the reference book and the glossary to which the present invention is applied; and  
         [0047]    [0047]FIG. 29 illustrates a workbook and a reference book to which the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0048]    With reference to the accompanying drawings, the present invention will become clear from the following description of embodiments of the present invention.  
         [0049]    Referring to FIG. 1, an e-book providing system to which the present invention is applied will now be described.  
         [0050]    A content database  11  records content data for displaying an e-book and object data relating to content in a predetermined file format.  
         [0051]    Content data is written in a markup language, such as XML (extensible Markup Language), and includes information to be played or displayed as the e-book, commands for playing or displaying the e-book, and, if necessary, statements for referencing other content data or object data. The XML is a markup language capable of defining not only a fixed markup method, such as HTML (HyperText Markup Language), but also a unique markup method and can describe the document structure in a simple format. Since XML can uniquely define tags, data can be written using a structure understandable to human beings. Also, data can be constructed flexibly.  
         [0052]    Object data is data that does not include a statement, for example, plain text data, image data, audio data, and video data. The object data is played or displayed when being referenced by the content data.  
         [0053]    A personal computer  12  reads content data or object data, which is written in XML, from the content database  11  and outputs the content data or the object data forming the e-book to various recording media, such as a magnetic disk  14 , an optical disk  15 , a magneto-optical disk  16 , or a semiconductor memory  17  (including a memory stick (registered trademark)) or an internal memory of an e-book player  18 , which is a dedicated player, and hence the content data or the object data can be recorded.  
         [0054]    The personal computer  12  downloads content data or object data to a user&#39;s PDA  21  or a personal computer  22  through the Internet  20 .  
         [0055]    Although one personal computer  12  is displayed, a plurality of personal computers  12  can be provided. When there is a plurality of publishers of e-publications, personal computers under management of the corresponding publishers are connected to the Internet  20 .  
         [0056]    Various recording media, such as the magnetic disk  15 , the optical disk  15 , the magneto-optical disk  16 , or the semiconductor memory  17 , can be installed in the PDA  21 , the personal computer  22 , or the e-book player  18  owned by an individual user.  
         [0057]    The PDA  21  or the personal computer  22  displays, on a display unit such as a display or a touchpanel, an e-book formed by content data or object data which is downloaded from the personal computer  12  through the Internet  20  and which is recorded in an internal memory or an e-book formed by object data or content data which is recorded in an installed recording medium (e.g., the magnetic disk  14 , the optical disk  15 , the magneto-optical disk  16 , or the semiconductor memory  17 ).  
         [0058]    The e-book player  18  displays, on a display panel, an e-book formed by content data or object data which is recorded therein beforehand or which is recorded therein by user processing or an e-book which is formed by content data or object data recorded in an installed recording medium. Also, the e-book player  18  can download content data or object data from the personal computer  12  through the Internet  20 .  
         [0059]    [0059]FIG. 2 shows the configuration of the personal computer  12  shown in FIG. 1.  
         [0060]    A CPU (Central Processing Unit)  31  receives signals corresponding to various commands input by a user using an input unit  34  through an input/output (I/O) interface  32  and an internal bus  33 , receives a control signal transmitted from another personal computer (e.g., the personal computer  22 ) through a network interface  40 , and performs various processes based on the input signals. A ROM (Read Only Memory)  35  stores a program used by the CPU  31  and basically-fixed data of parameters for arithmetic processing. A RAM (Random Access Memory)  36  stores a program executed by the CPU  31  and variable parameters that appropriately change in accordance with the execution of the program. The CPU  31 , the ROM  35 , and the RAM  36  are interconnected through the internal bus  33 .  
         [0061]    The internal bus  33  is also connected to the I/O interface  32 . The input unit  34  is formed by, for example, a keyboard, a touchpad, a jog dial, or a mouse and is operated when the user wants to input various commands to the CPU  31 . A display unit  37  is formed by, for example, a CRT (Cathode Ray Tube) or an LCD (Liquid Crystal Display) and displays various information using text or images.  
         [0062]    An HDD (Hard Disk Drive)  38  drives a hard disk and causes the hard disk to record or play a program executed by the CPU  31  or information. If necessary, the magnetic disk  14 , the optical disk  15 , the magneto-optical disk  16 , or the semiconductor memory  17  is installed in a drive  39 , and hence data can be exchanged.  
         [0063]    The network interface  40  is connected to the e-book player  18  through a predetermined cable and exchanges information with the e-book player  18 . Also the network interface  40  accesses the content database  11 , searches the content database  11  for necessary information, and reads the necessary information. Also the network interface  40  registers new data or updates registered data.  
         [0064]    The components from the input unit  34  to the network interface  40  are connected to the CPU  31  through the I/O interface  32  and the internal bus  33 .  
         [0065]    Since the configuration of the personal computer  22  owned by the user, which is connected to the personal computer  12  through the Internet  20 , is basically the same as that of the personal computer  12  described by referring to FIG. 2, a description thereof is omitted.  
         [0066]    [0066]FIG. 3 shows the configuration of the e-book player  18  shown in FIG. 1.  
         [0067]    A CPU  51  performs various processes based on signals corresponding to various commands input by the user using a key operation unit  52  and a control signal input through a communication unit  58 . A ROM  53  stores a program used by the CPU  51  and basically-fixed data of parameters for arithmetic processing. A RAM  54  stores a program executed by the CPU  51  and variable parameters which appropriately change in accordance with the execution of the program.  
         [0068]    An e-book ROM  55  records content data or object data which is input from the personal computer  12  or which is downloaded from the personal computer  12  through the Internet  20  and the communication unit  58 .  
         [0069]    A display controller  56  displays, under the control of the CPU  51 , various information using text or images on a display panel  57 . The display panel  57  is formed by, for example, a CRT or an LCD. Under the control of the display controller  56 , the display panel  57  displays various information using text or images.  
         [0070]    A drive  60  and the semiconductor memory  17  are connected to an interface  59 , thereby exchanging data. If necessary, the magnetic disk  14 , the optical disk  15 , or the magneto-optical disk  16  is installed in the drive  60 , and hence data can be exchanged.  
         [0071]    The communication unit  58  is connected to the personal computer  12 . To exchange information, the communication unit  58  accesses the personal computer  12  through the Internet  20 , searches the personal computer  12  for necessary information, and downloads the necessary information.  
         [0072]    Referring to FIG. 4, the internal configuration of the PDA  21  will now be described.  
         [0073]    A CPU  71  performs an operating system or various programs, such as a developed application program, which are stored in a flash ROM  73  or an EDO DRAM (Extended Data Out Dynamic Random Access Memory)  74  in synchronization with a clock signal supplied from an oscillator  72 .  
         [0074]    The flash ROM  73  is formed by a flash memory, which is one type of EEPROM (Electrically Erasable Programmable Read Only Memory). In general, the flash ROM  73  stores a program used by the CPU  71  and basically-fixed data of parameters for arithmetic processing. The EDO DRAM  74  stores a program executed by the CPU  71  and variable parameters which appropriately change in accordance with the execution of the program.  
         [0075]    A memory stick interface  75  reads data from a memory stick  91  installed in the PDA  21  and writes data supplied from the CPU  71  to the memory stick  91 .  
         [0076]    In synchronization with a clock signal supplied from the oscillator  77 , an USB (Universal Serial Bus) interface  76  receives data or a program from a drive  83 , which is a connected USB device, and supplies data supplied from the CPU  71  to the drive  83 . In synchronization with a clock signal supplied from the oscillator  77 , the USB interface  76  receives data or a program from a cradle  84 , which is a connected USB device, and supplies data supplied from the CPU  71  to the cradle  84 .  
         [0077]    The cradle  84  is a docking station for performing data synchronization by connecting, by wire, the PDA  21  and a personal computer and by performing so-called “hot sync” processing.  
         [0078]    The drive  83  is also connected to the USB interface  76 . The drive  83  reads data or a program recorded in the installed magnetic disk  14 , the optical disk  15 , the magneto-optical disk  16 , or the semiconductor memory  17  and supplies the data or the program through the USB interface  76  to the CPU  71  or the EDO DRAM  74  connected thereto. Also the drive  83  records data or a program supplied from the CPU  71  in the installed magnetic disk  14 , the optical disk  15 , the magneto-optical disk  16 , or the semiconductor memory  17 .  
         [0079]    The PDA  21  can establish a connection with a cellular phone or a PHS (Personal Handyphone System), thus allowing the PDA  21  to access the personal computer  12  through the Internet  20 .  
         [0080]    The flash ROM  73 , the EDO DRAM  74 , the memory stick interface  75 , and the USB interface  76  are connected to the CPU  71  through an address bus and a data bus.  
         [0081]    A display unit  90  receives data from the CPU  71  through an LCD bus and displays an image or a character corresponding to the received data. When a touchpad provided in the upper portion of the display unit  90  is operated, a touchpad controller  78  receives data corresponding to the operation (e.g., data indicating the coordinates of a touched position) from the display unit  90  and supplies a signal corresponding to the received data to the CPU  71  through a serial bus.  
         [0082]    An electroluminescence (EL) driver  79  activates an EL device provided at the back of the LCD of the display unit  90  and controls the brightness of the display unit  90 .  
         [0083]    An infrared communication unit  80  transmits data received from the CPU  71  through the medium of infrared radiation to another apparatus (not shown) through a universal asynchronous receiver-transmitter (UART). The infrared communication unit  80  also receives data through the medium of infrared radiation transmitted from another apparatus and supplies the received data to the CPU  71 . In other words, the PDA  21  can communicate with another apparatus through the UART.  
         [0084]    An audio playing unit  82  is formed by a speaker and a demodulator circuit for demodulating audio data. The audio playing unit  82  demodulates pre-stored audio data or audio data received through the Internet  20 , plays the audio data, and outputs sound. For example, the audio playing unit  82  plays audio data supplied from the CPU  71  through a buffer  81  and outputs sound corresponding to the data.  
         [0085]    A key  88  is formed by, for example, an input key. The key  88  is operated by the user when the user wants to input various commands to the CPU  71 .  
         [0086]    A jog dial  89  supplies to the CPU  71  data corresponding to an operation in which the jog dial  89  is rotated or pressed against a main body.  
         [0087]    A power supply circuit  87  transduces a power supply voltage supplied from a battery  85  attached thereto or an AC (Alternating Current) adapter  86  connected thereto and supplies power to the components from the CPU  71  to the audio playing unit  82 .  
         [0088]    Referring to FIG. 5, functional blocks in a case in which an e-book is played by, for example, the e-book player  18 , the PDA  21 , or the personal computer  22  will now be discussed.  
         [0089]    A tag information decoder  111  selectively reads a content file desired by a user from among content files  121 - 1  to  121 -n recorded in a file recording unit  113  or content files  123 - 1  to  123 -p recorded in an external recording unit  114  in accordance with information corresponding to user operation input from an operation input unit  112  and decodes tag information. The tag information decoder  111  also controls the recording of a new content file or a new resource file into the file recording unit  113 , which is input through a file input controller  117 .  
         [0090]    A resource file is a file referenced by a content file and basically corresponds to the foregoing object file. Tags can be included in the resource file. A tag for referencing another content file may be included in the content file.  
         [0091]    Specifically, the tag information decoder  111  analyzes tags in the selectively read content file of the content files  121 - 1  to  121 -n or  123 - 1  to  123 -p. If necessary, the tag information decoder  111  reads resource files  122 - 1  to  122 -m or  124 - 1  to  124 -q or a content file other than the first-selected content file, generates display data for the e-book, and outputs the display data to a display controller  115 .  
         [0092]    The display controller  115  receives the e-book display data and controls a display unit  116  to display the input e-book display data.  
         [0093]    The file recording unit  113  records, for example, data downloaded through the Internet  20  or data copied from various recording media. The file recording unit  113  records the content files  121 - 1  to  121 -n and the resource files  122 - 1  to  122 -m. The external recording unit  114  corresponds to various recording media, such as the above-described magnetic disk  14 , the optical disk  15 , the magneto-optical disk  16 , or the semiconductor memory  17 , or any apparatus capable of recording information. The external recording unit  114  records the content files  123 - 1  to  123 -p and the resource files  124 - 1  to  124 -q.  
         [0094]    Hereinafter the content files  121 - 1  to  121 -n are collectively referred to as content files  121  when it is unnecessary to distinguish between the individual content files  121 - 1  to  121 -n. The resource files  122 - 1  to  122 -m are collectively referred to as resource files  122  when it is unnecessary to distinguish between the individual resource files  122 - 1  to  122 -m. The content files  123 - 1  to  123 -p are collectively referred to as content files  123  when it is unnecessary to distinguish between the individual content files  123 - 1  to  123 -p. The resource files  124 - 1  to  124 -q are collectively referred to as resource files  124  when it is unnecessary to distinguish between the individual resource files  124 - 1  to  124 -q.  
         [0095]    A content displaying process will now be described by referring to the flowchart shown in FIG. 6.  
         [0096]    In step S 1 , the tag information decoder  111  determines whether or not a content (data corresponding to an e-book) display command from the operation input unit  112  is received, that is, whether or not an e-book read command input by a predetermined operation is received. If it is determined in step S 1  that no content display command is received, the processing in step S 1  is repeated until it is determined that a content display command is received.  
         [0097]    If it is determined in step S 1  that a content display command is received, in step S 2 , the tag information decoder  111  reads the specified content file  121  or  123  from the file recording unit  113  or the external recording unit  114 , respectively.  
         [0098]    In step S 3 , the tag information decoder  111  analyzes a tag in the content file  121  or  123  read in step S 2 . FIGS.  7  to  9  show examples of tags included in the content file  121  or  123 .  
         [0099]    Referring to FIG. 7, examples of command tags will now be described. GetInfo tag is a command for obtaining and displaying a file in accordance with a subsequent condition command or with a tag specifying a source for obtaining information. ContentRef tag is a command for obtaining and displaying information displayed in a predetermined portion of the content file  121  or  123  in accordance with the content file  121  or  123  specified by subsequent Bookid and in accordance with reference position information.  
         [0100]    CondT tag is a condition command for determining whether or not a condition included in the subsequent attribute is true. CondF is a condition command for determining whether or not a condition included in the subsequent attribute is false. CondT tag and CondF tag also determine the number of significant digits of the subsequent attribute data. For example, an absolute date discussed below can be written as YYYY/MM/DD when the absolute date including the day is specified. When only YYYY is included, whether or not the condition is satisfied can be determined only by year information. When the absolute date is written as MM/DD, attribute information thereof is determined as month/day, and whether or not the condition is satisfied is determined accordingly. GetFile tag specifies a source for obtaining information (for example, a URL or an absolute path or a relative path in a personal computer) and the filename of a saved file for saving the obtained information.  
         [0101]    Referring to FIG. 8, examples of tags for expressing attribute values will now be described. A Type attribute is included subsequent to condT or condF, which is a condition command. The Type attribute is a tag specifying the type of condition, such as time, date, or position. When position is used as a condition, the current position of the user is determined using GPS (Global Positioning System). An On attribute is included subsequent to the Type attribute. When the On attribute corresponds to (matches) the subsequent “date” information, it is determined that the condition is true (or false).  
         [0102]    A Passed attribute is included subsequent to the Type attribute. If the subsequent “period” has elapsed, it is determined that the condition is true (or false). When a predetermined period, such as one month, has passed since information was downloaded (copied) to a corresponding portion, the Passed attribute is used to download a new file or to prevent the downloaded file from being displayed. Accordingly, information subsequent to the Passed attribute is information indicating “period”, not “date”.  
         [0103]    A From attribute is included subsequent to the Type attribute. When the current date is subsequent to “date” information included subsequent to the From attribute, it is determined that the condition is true (false). A To attribute is included subsequent to the Type attribute. When the current date is prior to “date” information included subsequent to the To attribute, it is determined that the condition is true (false).  
         [0104]    An href attribute is included subsequent to the GetFile tag. The href attribute specifies the URL of a file obtaining source or an absolute path or a relative path in a personal computer. A FileName attribute is included subsequent to the href attribute. The FileName attribute specifies the filename of an obtained file. A RefbookID attribute is included subsequent to the ContentRef tag. The RefbookID attribute specifies the ID of the content file  121  or  123  to be referenced and, if necessary, a reference destination in the content file. A Replace attribute is included subsequent to the RefbookID attribute. The Replace attribute specifies data to be displayed instead when there is no content file  121  or  123  having the specified ID.  
         [0105]    An action attribute is included subsequent to the RefbookID attribute. The action attribute describes the type of operation input received to display the content file  121  or  123  having the specified ID. An icon attribute is included subsequent to the action attribute. The icon attribute specifies an icon to be displayed for receiving an operation input specified by the action attribute.  
         [0106]    Referring to FIG. 9, examples of modes of expressions for expressing dates subsequent to On, From, and To, which indicate attributes of a tag, will now be described. An absolute date is specified as YYYY/MM/DD. For example, when the absolute date is specified as 2001/01/01, it indicates Jan. 1, 2001. An absolute time is expressed as HH:MM(:SS). For example, when the absolute time is specified as 13:15, it indicates 13:15 (1:15 PM). In order to express month information indicating an arbitrary month every year, it is specified as MMm. For example, when the month information is specified as 05m, it indicates every May. In order to express day information indicating an arbitrary day every month, it is specified as DDd. For example, when the day information is specified as  10   d , it indicates every 10th day. Days of the week are described as “SUN”, “MON”, “TUE”, “WED”, “THU”, “FRY”, and “SAT”, which indicate Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday, respectively.  
         [0107]    In step S 4 , the tag information decoder  111  determines whether or not a tag included in the content file  121  or  123   
         [0108]    If it is determined in step S 4  that the tag included in the content file  121  or  123  is a GetInfo command, in step S 5 , a resource-file accessing process described below with reference to a flowchart shown in FIG. 10 is performed.  
         [0109]    If it is determined in step S 4  that the tag included in the content file  121  or  123  is not a GetInfo command, in step S 6 , the tag information decoder  111  determines whether or not the tag included in the content file  121  or  123  is a ContentRef command.  
         [0110]    If it is determined in step S 6  that the tag included in the content file  121  or  123  is a ContentRef command, in step S 7 , a specified-file reference process, which will be described with reference to a flowchart shown in FIG. 16, is performed.  
         [0111]    If it is determined in step S 6  that the tag included in the content file  121  or  123  is not a ContentRef command, in step S 8 , the tag information decoder  111  executes a displayable tag.  
         [0112]    After the processing in steps S 5 , S 7 , or S 8  is terminated, in step S 9 , the tag information decoder  111  can determine whether or not all the tags in the content file  121  or  123  have been executed.  
         [0113]    If it is determined in step S 9  that not all the tags in the content file  121  or  123  have been executed, the process returns to step S 3 , and the processing from step S 3  onward is repeated. If it is determined in step S 9  that all the tags in the content file  121  or  123  have been executed, the process is terminated.  
         [0114]    Accordingly, the tag information decoder  111  can display the e-book by reading the content file  121  or  123  specified by the user and by analyzing and executing tags in the content file  121  or  123 . In accordance with tag commands, if necessary, another content file  121  or  123  or the resource file  122  or  124  is read from a specified location and is displayed as part of the e-book. Hereinafter a method for reading and displaying the primary content file  121  or  123  and the reference destination, i.e., the content file  121  or  123  or the resource file  122  or  124 , will now be described in detail.  
         [0115]    The resource-file accessing process, which is performed in step S 5  in FIG. 6, will now be described by referring to  
         [0116]    In step S 21 , the tag information decoder  111  determines whether or not a tag for performing the process is a GetFile command.  
         [0117]    If it is determined in step S 21  that the tag is not a GetFile command, in step S 22 , the tag information decoder  111  determines whether or not the tag for performing the process is a condition command, such as condT or condF illustrated in FIG. 7, and whether or not a condition specified by an attribute value illustrated in FIG. 8 is satisfied. If it is determined in step S 22  that the tag for performing the process is a condition command, such as condT or condF, and that the condition specified by the attribute value, which is illustrated in FIG. 8, is satisfied, the process returns to step S 21 , and the processing from step S 21  onward is repeated.  
         [0118]    If it is determined in step S 22  that the tag for performing the process is not a condition command but is, for example, unanalyzable information, or if the tag for performing the process is a condition command though the condition is not satisfied, in step S 23 , the tag information decoder  111  generates data corresponding to a display screen for displaying, if necessary, pre-recorded object data or an error message and outputs the generated data to the display controller  115 . The display controller  115  controls the display unit  116  and causes the display unit  116  to display the display screen corresponding to the data supplied from the tag information decoder  111 . The process then returns to step S 9  in FIG. 6.  
         [0119]    If it is determined in step S 21  that the tag for performing the process is a GetFile command, in step S 24 , the tag information decoder  111  obtains a connection destination and the filename of a saved file for recording a file, which are used for downloading a file to be referenced through the file input controller  117  or for copying a file to be referenced from the external recording unit  114 , on the basis of information included in the tag, and for recording the file in the file recording unit  113 .  
         [0120]    For example, when it is specified that object data be downloaded from a predetermined WWW server, a URL of the corresponding WWW server is included in the GetFile tag. When object data recorded in an externally-connected device or in an internal recording unit is to be referenced, a path to the object data (a suitable path for referencing the object data is selected from an absolute path and a relative path) is specified.  
         [0121]    In step S 25 , the tag information decoder  111  connects to the connection destination specified by the information obtained in step S 24 , obtains the object data specified by the GetFile tag, and records the object data in the file recording unit  113 .  
         [0122]    In step S 26 , the tag information decoder  111  generates display data for displaying a display screen corresponding to content data including the obtained object data (that is, the resource file  122 ) and outputs the display data to the display controller  115 . The display controller  115  controls the display unit  116  to cause the display unit  116  to display a display screen corresponding to the data supplied from the tag information decoder  111 . The process then returns to step S 9  in FIG. 6.  
         [0123]    [0123]FIG. 11 shows one page of a guidebook (tourist information) provided as an e-book to which the present invention is applied. Preferably the guidebook always describes up-to-date information. On the other hand, the guidebook includes many pieces of substantially unvarying information, such as a description of the history of a corresponding region. If it is attempted to describe in the guidebook every piece of event information relating to festivals and regional events irrespective of time, the total amount of information would increase. In order to reduce the total amount of information, the description of each event needs to be reduced. To prevent such problems, whether or not information is directly described in the content file  121  or  123  or obtained from a specified location is determined depending on whether or not the information needs to be changed according to time.  
         [0124]    The page of the guidebook shown in FIG. 11 includes display areas  141  to  144 , the display of which is under the control of the resource-file accessing process. Portions other than the display areas  141  to  144  display the same data at any time, which means that text is included in the content data  121  or  123 .  
         [0125]    Referring to FIGS.  12  to  15 , a process of displaying the content file  121  or  123 , including tags for displaying the page of the guidebook shown in FIG. 11, will now be described.  
         [0126]    For example, when a townscape image relating to the content data  121  is to be displayed in the display area  141 , the image is updated from time to time. Accordingly, the e-book can have added value.  
         [0127]    In such a case, as shown in FIG. 12, a GetFile command following a GetInfo command specifies, subsequent to href, the location of a site storing image data, i.e., http://www.aaa.com/files. Subsequent to FileName=, the filename town.jpg to be given to the downloaded image is specified.  
         [0128]    In the tag shown in FIG. 12, only the URL of the site storing the image data is included; no filename of the image data to be downloaded is specified. For example, when a specified connection destination has a plurality of files recorded therein, all the files are downloaded. When a plurality of files is downloaded, filenames are determined so that the individual files can be distinguished by automatically assigning a number to each file, such as Town1.jpg, Town2.jpg, Town3.jpg, etc.  
         [0129]    In order to display a weekly weather forecast relating to the content data  121  in the display area  142  and a monthly weather forecast relating to the content data  121  in the display area  143 , for example, as shown in FIG. 13, a condition command condT is included between a GetInfo command and a GetFile command. Data specified by the subsequent GetFile command is obtained only if a condition indicated by the condition command condT is satisfied.  
         [0130]    More specifically, it is assumed that &lt;condT Type=“day” On=“WED”/&gt; is included. When it is Wednesday, a file specified by the URL and filename (http://ww.aaa.com/weth/xxx.txt), which is specified subsequent to href, is downloaded in accordance with the GetFile tag. The downloaded file is stored under the filename WeekWeather.text as the resource file  122  in the file recording unit  113  and is displayed in the display area  142 . When it is assumed that &lt;condT Type=“day” On=“Old/&gt;is specified, a file specified by the URL and filename (http://www.aaa.com/weath/yyy.text), which is specified subsequent to href, is downloaded on the first day every month. The downloaded file is stored under the filename MonthWeather.text as the resource file  122  in the file recording unit  113  and is displayed in the display area  143 .  
         [0131]    The GetFile commands shown in FIG. 13 specify the filenames of files to be downloaded. For example, as shown in FIG. 13, a predetermined URL stores a plurality of pieces of data. When the user wants to selectively display desired data from among these pieces of data, the filenames need to be defined in the GetFile commands.  
         [0132]    When predetermined data, such as a time-limited coupon, is to be displayed in the display area  144  only for a specified period, as shown in FIG. 14, a condition command condT is included between a GetInfo command and a GetFile command. As a condition, the period start date and end date are specified.  
         [0133]    More specifically, it is assumed that &lt;condT Type=“day” From=“2001/05/19” To=“2001/11/19”/&gt; is specified. During the period from May 19, 2001 to Nov. 19, 2001, a file specified by the URL and filename (http://www.aaa.com/happy/present.txt), which is specified subsequent to href, is downloaded in accordance with the GetFile tag. The downloaded file is stored under the filename present.txt as the resource file  122  in the file recording unit  113  and is displayed in the display area  144 .  
         [0134]    Accordingly, an e-book having a mixture of information that needs to be updated frequently, information that does not need to be updated for a relatively long period, and information that does not need to be updated at all can be provided to the user. Also, information can be updated automatically (i.e., so-called background processing) without the user consciously performing a special operation, such as accessing a predetermined WWW server through the Internet and downloading information.  
         [0135]    When no filename is specified subsequent to href and when a specified file obtaining source has a plurality of files, all the files recorded in the file obtaining source are downloaded, and the downloaded files are automatically numbered and stored as the resource files  122  in the file recording unit  113 . For example, all the files can be displayed in a list in a specified display area. Alternatively, the files can be displayed one at a time by switching the file type to be displayed at predetermined intervals, such as every 10 seconds or every 30 seconds.  
         [0136]    For example, when a source for obtaining the resource files  122  or  124  to be displayed in the display area  141  shown in FIG. 11 stores a plurality of landscape images, such as those shown in FIG. 15, the tag information decoder  111  can display the plurality of landscape images in the display area  141  by switching the image to be displayed at predetermined intervals. Thus, up-to-date information relating to content can be delivered to many users in limited space on a page. This can enhance user&#39;s enjoyment in viewing the page.  
         [0137]    The specified-file reference process performed in step S 7  of FIG. 6 will now be described by referring to the flowchart shown in FIG. 16.  
         [0138]    In step S 41 , the tag information decoder  111  reads a statement(s) subsequent to ContentRef in the corresponding content file  121  or  123 . In step S 142 , it is determined whether or not data specified as a reference destination included subsequent to RefbookID is stored in the file recording unit  113  or the external recording unit  114 .  
         [0139]    [0139]FIG. 17 shows a source of the content file  121  or  123  describing a recipe as an example of the content file  121  or  123  of an e-book to which the present invention is applied.  
         [0140]    In the content file  121  or  123 , processing in accordance with tags included therein is performed. For example, the text “Egg Sunny-Side Up” is displayed as a main title, and image data specified by the filename “eggsunnysideupserving.Bmp” is displayed. Since there is a ContentRef tag at the head of an other-content reference portion  151 , the specified-file reference process shown in FIG. 16 is performed. Since “00000002#2” is specified as a RefbookID attribute, it is determined in step S 42  whether or not the content file  121  or  123  having the BookID 00000002 is recorded in the file recording unit  113  or the external recording unit  114 , respectively.  
         [0141]    The BookID tag is a unique number assigned to the content file  121  or  123 . Not all content files need to have BookID, although BookID needs to be assigned at least to a content file to be referenced by the specified-file reference process.  
         [0142]    If it is determined in step S 42  that there is data specified as the reference destination included subsequent to the RefbookID attribute, the tag information decoder  111  determines in step S 43  whether or not an action attribute is specified subsequent to the RefbookID attribute.  
         [0143]    If it is determined in step S 43  that no action attribute is specified, in step S 44 , the tag information decoder  111  reads the data specified as the reference destination from the file recording unit  113  or the external recording unit  114 . The tag information decoder  111  generates display image data for displaying, at a predetermined position, reference-destination data in a size specified by a width attribute and a height attribute in the other-content reference portion  151  in the content file  121  or  123  (wherein in this case the width is 70% and the height is 30% relative to the basic content screen size) and outputs the generated data to the display controller  115 . The display controller  115  controls the display unit  116  to display a display image corresponding to the supplied display image data.  
         [0144]    [0144]FIG. 18 shows an example of data specified as a reference destination included subsequent to the RefbookID attribute. In the content file  121  or  123  edited for performing the specified-file reference process, a BookID tag is included at the top thereof. The BookID is included between &lt;BookID&gt; and &lt;/BookID&gt;. The BookID a unique number assigned to each e-book. The content file  121  or  123  having the BookID tag is provided with a reference area  161  enclosed by &lt;Float&gt; and &lt;/Float&gt;. One content file  121  or  123  may have a plurality of reference areas  161 . Float tags may be defined for all pieces of data in the content file  121  or  123 .  
         [0145]    Since a display screen displayed by the content file  121  or  123  shown in FIG. 17 includes information in the reference area  161  shown in FIG. 18, a display screen shown in FIG. 19 is displayed. The information in the display area  161  shown in FIG. 18 is displayed in a display area  171 .  
         [0146]    If it is determined in step S 43  that an action attribute is specified, the tag information decoder  111  displays, in step S 45 , a predetermined icon specified by a subsequent icon attribute.  
         [0147]    [0147]FIG. 20 shows an example of a source of the content file  121  or  123  in which an action attribute is specified.  
         [0148]    Referring to FIG. 20, a tag  181  includes attributes subsequent to ContentRef. Subsequent to a RefbookID attribute, the tag  181  includes an action attribute, an icon attribute, and a reference-data display method to be performed when a specified operation is performed on an icon.  
         [0149]    [0149]FIG. 21 shows a display image corresponding to the content file  121  or  123  shown in FIG. 20. As shown in FIG. 21, an icon  191  is displayed at a corresponding position in the content file  121  or  123 . When it is determined by a process described below that the operation indicated by the action attribute is performed, the reference data is displayed in accordance with the attributes included in the tag  181 .  
         [0150]    In step S 46 , the tag information decoder  111  determines whether or not the operation specified by the action attribute is input (received) on the basis of a signal input from the operation input unit  112 . If it is determined in step S 46  that the specified operation is not input (received), the processing in step S 46  is repeated until the specified operation is input.  
         [0151]    If it is determined in step S 46  that the specified operation is input (received), in step S 47 , the tag information decoder  111  determines whether or not “#” is included in a sequence subsequent to “RefbookID=”.  
         [0152]    If it is determined in step S 47  that “#” is included in the sequence subsequent to “RefbookID=”, in step S 48 , the tag information decoder  111  stores a sequence prior to “#” in the sequence subsequent to “RefbookID=” as a book title ID. In step S 49 , the tag information decoder  111  stores a sequence subsequent to “#” in the sequence subsequent to “RefbookID=” as a reference destination ID.  
         [0153]    If it is determined in step S 47  that no “#” is included in the sequence subsequent to “RefbookID=”, in step S 50 , the tag information decoder  111  stores the sequence subsequent to “RefbookID=” as a book title ID and a predetermined symbol (e.g., a predetermined character string) indicating the “top” as a reference destination ID.  
         [0154]    After the processing in step S 49  is terminated or after the processing in step S 50  is terminated, in step S 51 , the tag information decoder  111  searches the file recording unit  113  and the external recording unit  114  for an e-book (corresponding to the content file  121  or  123 ) specified as the reference destination.  
         [0155]    In step S 52 , the tag information decoder  111  determines whether or not the reference destination ID stored in step S 49  or in step S 50  is a predetermined symbol indicating the “top”.  
         [0156]    If it is determined in step S 52  that the reference destination ID is a predetermined symbol indicating the “top”, in step S 53 , a jumping process of jumping to the top page, which will be described below using a flowchart shown in FIG. 23, is performed. The process then returns to step S 9  in FIG. 6.  
         [0157]    If it is determined in step S 52  that the reference destination ID is not a predetermined symbol indicating the “top”, in step S 54 , a process of displaying a specified reference portion, which will be described using a flowchart shown in FIG. 25, is performed. The process then returns to step S 9  in FIG. 6.  
         [0158]    If it is determined in step S 42  that no data specified as the reference destination included subsequent to the RefbookID attribute is detected, the tag information decoder  111  determines in step S 55  whether or not an action attribute is specified.  
         [0159]    If it is determined in step S 55  that no action attribute is specified, the tag information decoder  111  generates in step S 56  display data for displaying data subsequent to “replace=” and outputs the generated display data to the display controller  115 . The display controller  115  controls the display unit  116  to display a display screen corresponding to the data supplied from the tag information decoder  111 . The process then returns to step S 9  in FIG. 6.  
         [0160]    More specifically, if there is no data specified as the reference destination included subsequent to the RefbookID attribute in the content file  121  or  123  illustrated in FIG. 17, that is, if there is no content file  121  or  123  illustrated in FIG. 18, as shown in FIG. 22, a display area  201  displays, in place of the specified data, information included subsequent to “replace=”.  
         [0161]    If it is determined in step S 55  that an action attribute is specified in step S 56 , the tag information decoder  111  generates display data for displaying nothing at a specified position and outputs the generated display data to the display controller  115 . The display controller  115  controls the display unit  116  to display a display screen corresponding to the data supplied from the tag information decoder  111 . The process then returns to step S 9  in FIG. 6.  
         [0162]    Accordingly, information can be shared among a plurality of e-books. Information can be displayed as if it were described in an e-book being read. Also the user can be informed of whether or not there is data to be referenced. A message prompting the user to purchase an e-book required to display detailed information can be displayed.  
         [0163]    The jumping process of jumping to the top page, which is performed in step S 53  in FIG. 16, will now be described by referring to the flowchart shown in FIG. 23.  
         [0164]    In step S 71 , the tag information decoder  111  reads the detected reference-destination content file from the file recording unit  113  or the external recording unit  114 .  
         [0165]    In step S 72 , the tag information decoder  111  generates display data for opening and displaying the top portion of the content file read in step S 71  and outputs the generated display data to the display controller  115 . The display controller  115  controls the display unit  116  to display a display screen corresponding to the data supplied from the tag information decoder  111 . The process then returns to step S 9  in FIG. 6.  
         [0166]    The jumping process of jumping to the top page, which is illustrated with reference to the flowchart shown in FIG. 23, is performed in a case shown in FIG. 24. Specifically, a novel or a cartoon is in a plurality of volumes. In order to display from the last part of one volume of an e-book to the first part of the subsequent volume of the e-book, the jumping process is performed.  
         [0167]    In this case, an icon subjected to an action is displayed as, for example, in FIG. 24, an icon  211  displayed at the last part of the first volume. When the icon  211  is subjected to a specified action, such as when the icon  211  is clicked, the top page of the second volume is opened. When there is no content file  121  or  123  corresponding to the second volume in the file recording unit  113  or the external recording unit  114 , the icon  211  is not displayed (due to the processing in step S 57  in the specified-file reference process illustrated using FIG. 16).  
         [0168]    The process of displaying a specified reference portion, which is performed in step S 54  in FIG. 16, will now be described by referring to the flowchart shown in FIG. 25.  
         [0169]    In step S 91 , the tag information decoder  111  reads the detected content file at the reference destination from the file recording unit  113  or the external recording unit  114 .  
         [0170]    In step S 92 , the tag information decoder  111  searches the read content file for a reference portion indicated by the reference destination ID included in the &lt;Float&gt; tag.  
         [0171]    In step S 93 , the tag information decoder  111  determines whether or not the reference portion indicated by the reference destination ID is detected.  
         [0172]    If it is determined in step S 93  that no reference portion indicated by the reference destination ID is detected, in step S 94 , the tag information decoder  111  determines whether or not the content file is searched to the end. If it is determined in step S 94  that the content file is not searched to the end, the process returns to step S 92 , and the processing from step S 92  onward is repeated.  
         [0173]    If it is determined in step S 93  that the reference portion indicated by the reference destination ID is detected, the tag information decoder  111  reads in step S 95  a display method specified by a tag subsequent to the tag indicating the reference destination. The display method includes, for example, a method of opening another window and causing this window to display reference-portion information and a method of opening a popup window and causing the popup window to display reference-portion information.  
         [0174]    In step S 96 , the tag information decoder  111  reads and analyzes a corresponding style sheet on the basis of the display method read in step S 95 . A style sheet is a display image template prepared in advance for each display format. For example, when the display method uses windows, a window containing no information is read as a template for displaying windows. When the display method uses popup windows, a popup window containing no information is read as a template for displaying popup windows.  
         [0175]    In step S 97 , the tag information decoder  111  determines the display size with reference to the amount of information included therein, generates a display window, and reads data for the detected reference portion.  
         [0176]    In step S 98 , the tag information decoder  111  generates display data by inserting text data or image data for the reference portion, which is read in step S 97 , into the window or the popup window, which is generated in step S 97 .  
         [0177]    In step S 99 , the tag information decoder  111  outputs the display data, which is generated in step S 98 , to the display controller  115 . The display controller  115  controls the display unit  116  to display a display window or a popup window corresponding to the supplied display data. The process then returns to step S 9  in FIG. 6.  
         [0178]    If it is determined in step S 94  that the file is searched to the end, the tag information decoder  111  generates in step S 100  data corresponding to a display screen for displaying an error message and outputs the generated data to the display controller  115 . The display controller  115  controls the display unit  116  to display an error message corresponding to the supplied display data. The process then returns to step S 9  in FIG. 6.  
         [0179]    [0179]FIG. 26 shows a display screen when the icon  191 , which is described using FIG. 21, is clicked. In this case, a display screen  221  showing the reference portion is displayed at a position specified by a tag. Since the tag  181 , which is described using FIG. 20 corresponding to the display screen shown in FIG. 21, specifies popuppos=“upper”, the display window  221  is displayed so as to overlap a first-displayed page.  
         [0180]    Referring to FIGS.  27  to  29 , examples of the utilization of the above-described process of displaying a specified reference portion in different cases will now be described.  
         [0181]    For example, as shown in FIG. 27, an e-book corresponding to a reference book has the content file  121  or  123 . In the content file  121  or  123 , a ContentRef tag is included in a text portion enclosed by &lt;P&gt; and &lt;/P&gt;, and a specified BookID tag value is 00000001. A book corresponding to this tag value is a glossary having the content file  121  or  123 . In such a case, based on the ContentRef tag and on tags and information included subsequent to the ContentRef tag, as shown in FIG. 28, an icon  231  is displayed between corresponding text portions (between “In XML” and “ISO/IEC 10646”) of a corresponding page of the reference book. When the icon  231  is clicked, a corresponding reference portion  233  of the glossary is displayed on a popup window  232 .  
         [0182]    The icon  231  can be displayed at any position on a display screen of an e-book, such as between text portions. With such a utilization method, a user who wants to utilize an e-book for studying can improve learning efficiency. When there is no content file  121  or  123  to be referenced, the unnecessary icon  231  is not displayed. The larger the number of related e-books the user purchases, the larger the number of icons to be displayed to indicate related information becomes. Accordingly, a series of products can have greater added value.  
         [0183]    Similar advantages can be achieved by related e-books, namely, a workbook and a reference book. For example, as shown in FIG. 29, a user has both a predetermined workbook and a reference book. In the user&#39;s workbook, an icon  241  and an icon  242  for displaying explanation of corresponding portions of the reference book are displayed. When the icon  241  is clicked or when the mouse is placed over the icon  241  (that is, when a predetermined operation is performed on the icon  241 ), a corresponding explanation portion  243  of the reference book is displayed. When the icon  242  is clicked or when the mouse is placed over the icon  242  (that is, when a predetermined operation is performed on the icon  242 ), a corresponding explanation portion  244  of the reference book is displayed. Accordingly, the user&#39;s learning efficiency can be improved, and a series of products can have greater added value.  
         [0184]    At an e-book publisher side, according to the present invention, e-book information can be shared among a plurality of e-books. When it is necessary to include the same data in a plurality of e-books, including all pieces of data in each e-book may make it difficult to include all necessary information since each recording medium has a limited recording capacity. According to the present invention, e-books can be edited so that information can be read from another e-book or another information source depending on the degree of importance of information.  
         [0185]    In the foregoing processes, e-books mainly containing image data or text data have been described. However, similar processes can be performed when e-books include audio data or video data.  
         [0186]    The above-described series of processes can be performed by software. Software can be installed by installing, from a recording medium, a program forming the software into a computer included in dedicated hardware or into a general personal computer capable of performing various functions by installing various programs.  
         [0187]    The recording medium includes, as shown in FIGS.  1  to  4 , package media having a program recorded therein, which is to be distributed, aside from a computer, to provide users with the program. The package media includes the magnetic disk  14  (including flexible disk), the optical disk  15  (including CD-ROM and DVD (Digital Versatile disk)), the magnetooptical disk  16  (including MD (Mini-Disk)), or the semiconductor memory  17 .  
         [0188]    In the description, steps for writing the program recorded in the recording medium include not only processing performed in time series in accordance with the written order but also parallel or discrete processing performed not necessarily in time series.  
         [0189]    In the present description, the system represents an overall apparatus formed by a plurality of apparatuses.