Abstract:
A web-crawling robot retrieves information from a web server that tailors information content to the capability of an accessing device. A link deriving unit in a proxy server for relaying data exchanged between the robot and the site analyzes a response from the site to the robot, and acquires information on a user agent corresponding to a particular kind of content of a link destination. On the basis of the information, a user agent information editing unit in the proxy server adds user agent information to the content retrieval request from the web-crawling robot to the site so as to disguise it as a content retrieval request issued from a given user agent, thereby acquiring a response corresponding to capabilities of the user agent.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a search engine used for searching information on the Internet, and more particularly to a web-crawling robot for automatically collecting such information.  
         BACKGROUND  
         [0002]    Today, various services are provided via networks, especially by the Internet. Various types of client devices that can be connected to the network range from high performance computers such as a personal computers and work stations to simple terminals such as mobile phones and personal digital assistants (PDAs) that are suitable mainly for receiving, displaying, and performing simplified processes. Therefore, many web sites (web servers) dynamically create different kinds of content to provide services according to the capabilities of connected client devices or user agents.  
           [0003]    A web server that returns web content according to the type of the client device can identify the type of the client device by referring to a User-Agent HTTP header in the HTTP (Hypertext Transfer Protocol) request from the client device. Using this mechanism, the server can create and return web content that is tailored according to the capability of the client.  
           [0004]    Tailoring the content according to the capability of the client device means that, for example, the content is segmented according to the client&#39;s memory capacity (i.e., the size of data that can be read at one time) and downloaded in multiple segments, or the content of text is altered to exclude images for client devices without the capability to display images.  
           [0005]    It is now commonplace to use a search engine or search site to select and acquire desired content from the enormous storehouse of information provided by the world wide web. The search site acquires in advance and holds information about gaining access to the content of the web and returns the information to the client upon request. One of the principal search sites today uses a robot for automatically gaining access to a site on the network while following a hyperlink (hereinafter referred to as a link) to the content, collecting the information for accessing the content at the site, and responding to the search request from the client device. For example, such systems are described in Japanese Published Unexamined Patent Applications No. 2002-215642 and No. 2002-259432.  
           [0006]    [0006]FIG. 17 is a block diagram showing the configuration of a robot type search site. As shown in FIG. 17, the robot type search site  1710  comprises a web-crawling robot  1711  for automatically gaining access to a site  1720  on a network to acquire information for accessing the content at the site, a database  1712  for registering and accumulating the information acquired from the web-crawling robot  1711 , and a search engine  1713  for searching the database  1712  by accepting a search request from a client device  1730  and returning the search result.  
           [0007]    As described above, at the robot type search site, the web-crawling robot gains access to the site on the network, and acquires the information (e.g., URL (uniform resource locators)) for accessing the content. However, when the web-crawling robot gains access to a site that dynamically creates content according to the capability of the client, the site recognizes the access as being from the web-crawling robot, and responds accordingly. Unfortunately, this means that the web-crawling robot cannot acquire all of the different adaptations of the information potentially provided by the site according to the clients&#39; capabilities. Also, some sites may invoke an error processing routine for the unknown type of access, or just assume an appropriate type. These actions may degrade the reliability of the search site.  
           [0008]    Assume, for example, that a site S 1  has content C 1  of size 5 KB, which may be sent in two ways. The first way is to send the 5 KB as a single block to a client device A that has a maximum readable data capacity of, for example, 6 KB. The second way is to segment the content and send the segments sequentially as c 01 , c 02  and c 03 , of 2 KB, 2 KB, and 1 KB, respectively, to a client B that has a maximum readable data capacity of 2 KB.  
           [0009]    At the time of the search by the web-crawling robot, the site S 1  determines that the web-crawling robot is the client device A. Thus, only the content C 1  having a size of 5 KB is registered in the database at the search site S 2 .  
           [0010]    Now suppose that the client device B retrieves the content associated with a predetermined search term at the search site S 2 , and hits the content C 1 . When the client device B sends an HTTP request to the site S 1  in accordance with this search result, the content c 01  that is one of three segments is returned from the site S 1 , as described above. At this time, if the hit search term exists in the content c 02  or c 03 , the client device B cannot obtain the desired information, even though it has made its access on the basis of the search results at the search site S 2 .  
           [0011]    The aforementioned Japanese Published Unexamined Patent Application No. 2002-259432 discloses a technique for analyzing the substance of the content to calculate and evaluate the degree to which the predetermined content is suitable for the client device, and choosing the search result that is most appropriate for the type of client device to the extent possible. However, the disclosed technique does not allow for the acquisition of content in consideration of the various types of client devices when the web-crawling robot collects the content.  
         SUMMARY  
         [0012]    Thus, an object of the present invention is to enable a site to acquire information on contents classified by type of corresponding terminal from sites that dynamically create the content, and to return an individual response according to the type of client device when a web-crawling robot collects information.  
           [0013]    In order to accomplish the above and other objects, the present invention includes a server that comprises a proxy function unit for relaying data exchanged between a site on a network and a web-crawling robot collecting contents by accessing the site, a link deriving unit for expanding a link concerned and acquiring information on a user agent corresponding to the content of a link destination concerned when the proxy function unit receives a response from the site to a content retrieval request issued from the web-crawling robot to the site and if the link destination of the link included in the response has content that individually returns different responses according to the type of user agent which is an access source, and a user agent information editing unit for converting user agent information included in the content retrieval request to the user agent information corresponding to the content of the link destination when the proxy function unit receives the content retrieval request from the web-crawling robot issued on the basis of the derived link.  
           [0014]    This server may further comprise a database for registering in association the location information (URL) of the content that individually returns different responses according to the type of user agent which is the access source and the user agent information corresponding to the content. In this case, the link deriving unit searches the database with the URL information of the link destination of the link included in the response as an argument to acquire the information of the user agent. Also, the user agent information editing unit converts the information of the content retrieval request, employing the user agent information obtained from the database.  
           [0015]    Also, the invention includes a server that comprises first transmitter-receiver means for exchanging data with a web-crawling robot, editing means for converting user agent information, which is included in a content retrieval request from the web-crawling robot to the site, received by the first transmitter-receiver means to specific user agent information for disguising it as a content retrieval request issued from a predetermined user agent, and second transmitter-receiver means for exchanging data with the site and sending the user agent information converted to the content retrieval request by the editing means to the destination site.  
           [0016]    This server may further comprise analysis means for analyzing the response from the site to the web-crawling robot, received by the second transmitter-receiver means. In this case, the editing means designates the predetermined user agent on the basis of the information analyzed by the analysis means and converts the user agent information of the content retrieval request to the user agent information of the designated user agent.  
           [0017]    Preferably, in this server, the analysis means replaces the link destination information of the link with the dummy information including identification information for identifying the user agent corresponding to the content of the link destination to cause the first transmitter-receiver means to send it to the web-crawling robot, if the link destination of the link included in the response has the content that individually returns responses according to a type of user agent which is an access source. Further, the editing means restores the dummy information to original link destination information, when the first transmitter-receiver means receives a content retrieval request issued from the web-crawling robot with the dummy information as a destination, and converts the user agent information included in the content retrieval request to the user agent information of the user agent designated by the identification information included in the dummy information.  
           [0018]    The invention also include a server that comprises a proxy function unit for relaying data exchanged between a web site on a network and a web-crawling robot collecting information by accessing the web site, a link deriving unit for replacing uniform resource locators (URL) to be a link destination of a link included in a response concerned with substitute URL individually corresponding to the user agent corresponding to a web content concerned when the proxy function unit receives a response from the web site to a content retrieval request issued from the web-crawling robot to the web site and if the link destination of the link included in the response has the web content that individually returns different responses according to a type of user agent which is an access source, a URL conversion unit for replacing the substitute URL with the original URL of the link destination when the proxy function unit receives a content retrieval request issued from the web-crawling robot to the substitute URL as a destination, and a user agent information editing unit for converting user agent information at a hypertext transfer protocol (HTTP) header of the content retrieval request to the user agent information corresponding to the substitute URL when the proxy function unit receives the content retrieval request issued from the web-crawling robot to the substitute URL as a destination.  
           [0019]    The above servers may be part of the server having the web-crawling robot, or part of the server having the web site. Moreover, apart from these servers, the server machine may be provided on the network.  
           [0020]    The invention also includes a method of collecting information from a site on a network as follows. That is, the information collecting method comprises a step of receiving a response from the site to a content retrieval request issued to the predetermined site and, if a link destination of a link included in the received response has content that individually returns different responses according to the type of user agent which is an access source, deriving the link and acquiring information on a user agent corresponding to the content of the link destination, a step of sending a content retrieval request having additional information for disguising it as a content retrieval request issued from the user agent to the link destination of the link included in the response on the basis of the user agent information, and a step of acquiring a response according to the type of user agent from the link destination.  
           [0021]    The invention also includes a method of collecting information, comprising a first step of receiving a response from the site to a content retrieval request issued from a predetermined web-crawling robot to the predetermined site and, if a link destination of a link included in the received response has a web content that individually returns different responses according to a type of user agent which is an access source, replacing URL which is the link destination of the link included in the response with substitute URL individually corresponding to the user agent corresponding to the web content and sending it to the web-crawling robot which is a destination of sending the response, a second step of receiving the content retrieval request issued from the web-crawling robot to the substitute URL as a destination, replacing the substitute URL with the original link destination URL, converting user agent information at an HTTP header of the content retrieval request to information on the user agent corresponding to the substitute URL, and sending it to the link destination, and a third step of receiving a response from the link destination to the content retrieval request whose user agent information was converted, adding identification information of the user agent to the response, and sending it to the web-crawling robot.  
           [0022]    Moreover, this invention also includes a program for implementing the functions of the server by controlling the computer, and a program for causing the computer to execute the steps of the information acquisition method. Programs may be distributed and stored in magnetic disks, optical disks, semiconductor memory, or other storage units, or distributed and provided via the network. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a diagram for explaining the concept of a robot search according to the present invention.  
         [0024]    [0024]FIG. 2 is a block diagram showing an exemplary configuration in which a transcoding proxy of the invention is provided with a web-crawling robot in a search server.  
         [0025]    [0025]FIG. 3 is a block diagram showing the configuration in which a transcoding proxy of the invention is provided in a predetermined proxy server on the network.  
         [0026]    [0026]FIG. 4 is a block diagram showing the configuration in which a transcoding proxy of the invention is provided with a site in a content server.  
         [0027]    [0027]FIG. 5 is a block diagram showing a typical example of the hardware configuration of a computer apparatus suitable for implementing a server with the transcoding proxy according to an embodiment of the invention.  
         [0028]    [0028]FIG. 6 is a block diagram showing an exemplary functional configuration of the transcoding proxy according to the invention.  
         [0029]    [0029]FIG. 7 is a table showing exemplary information registered in a diversity URL database.  
         [0030]    [0030]FIG. 8 is a flowchart for explaining the operation of a link deriving unit in accordance with the invention.  
         [0031]    [0031]FIG. 9 is a flowchart for explaining the details of an expansion process into a dummy link of FIG. 8.  
         [0032]    [0032]FIG. 10 is a flowchart for explaining the operation of a URL conversion unit and a user agent information editing unit according to the invention.  
         [0033]    [0033]FIG. 11 is a view showing a configuration example of the content collected.  
         [0034]    [0034]FIG. 12 is a diagram for explaining a process in which a web-crawling robot collects the content information as shown in FIG. 11.  
         [0035]    [0035]FIG. 13 is a diagram for explaining a process for making the link expansion to a response from the site to the web-crawling robot.  
         [0036]    [0036]FIG. 14 is a diagram for explaining a process with data flow for making a request from the web-crawling robot to the site.  
         [0037]    [0037]FIG. 15 is a block diagram schematically showing the configuration of a search server.  
         [0038]    [0038]FIG. 16 is a flowchart for explaining the operation of a search engine when accepting a search request from the client device.  
         [0039]    [0039]FIG. 17 is a block diagram showing the schematic configuration of a robot type search site. 
     
    
     DETAILED DESCRIPTION  
       [0040]    Preferred embodiments of this invention will be described below in detail with reference to the accompanying drawings.  
         [0041]    [0041]FIG. 1 is a diagram for explaining the concept of a robot search according to the present invention. As shown in FIG. 1, a transcoding proxy  10  for converting a request from the web-crawling robot  310  and a response from the site  210  is interposed between a web site  210  for providing the content and a web-crawling robot  310  for performing the robot search. Thereby, in collecting the information by robot search, it is possible to acquire information on content, classified by the type of client device, from a site that dynamically creates and tailors the content according to the type of client device.  
         [0042]    FIGS.  2  to  4  are diagrams that help explain aspects of exemplary embodiments of the invention.  
         [0043]    In the example of FIG. 2, the transcoding proxy  10 , together with the web-crawling robot  310 , is provided in a search server  300  (i.e., the server providing the functions at a search site). In this configuration, the web-crawling robot  310  accesses each site  210  on a network via the transcoding proxy  10 .  
         [0044]    In the example of FIG. 3, the transcoding proxy  10  is independently provided in a proxy server (intermediate site)  100  on the network. In this configuration, the web-crawling robot accesses the intermediate site and via the transcoding proxy  10  to each web site  210 .  
         [0045]    In the example of FIG. 4, the transcoding proxy  10 , together with the web server  212 , is provided in a web site  211 . In this configuration, each web-crawling robot  310  on the network gains access to the site  212  in the web site  211  via the transcoding proxy  10 .  
         [0046]    [0046]FIG. 5 is a block diagram showing a typical example of the hardware configuration of a computer apparatus suitable for implementing the servers (search server  300 , proxy server  100  and content server  200 ) with the transcoding proxy as shown in FIGS.  2  to  4 .  
         [0047]    The computer apparatus shown in FIG. 5 comprises a CPU (Central Processing Unit)  101  as operation means, a main memory  103  connected via an M/B (Mother Board) chip set  102  and a CPU bus to the CPU  101 , and a video card  104  connected via the M/B chip set  102  and an AGP (Accelerated Graphics Port) to the CPU  101 , a hard disk  105 , a network interface  106  and a USB port  107  connected via a PCI (Peripheral Component Interconnect) bus to the M/B chip set  102 , and a floppy disk drive  109  and a keyboard/mouse  110  connected via the PCI bus, a bridge circuit  108  and a low speed bus such as an ISA (Industry Standard Architecture) bus to the M/B chip set  102 .  
         [0048]    [0048]FIG. 5 is illustrative rather than limiting of the hardware configuration of the computer apparatus for realizing the invention. Various other configurations may be suitable as well. For example, instead of the video card  104 , a video memory may be included to process the image data in the CPU  101 , or a CD-ROM (Compact Disc Read Only Memory) or DVD-ROM (Digital Versatile Disc Read Only Memory) drive may be provided via the interface such as ATA (AT Attachment).  
         [0049]    In the following embodiment, the world wide web and Internet will be used to illustrate aspects of the invention. That is, at the site  210  of FIG. 1, various kinds of web content (e.g., a Web page or its object) are held. The web-crawling robot  310  sends an HTTP request to the site  210 , and receives an HTTP response therefrom. In this embodiment, the site  210  may be an ordinary web site, and the web-crawling robot  310  may be the ordinary web-crawling robot that is conventionally employed for web search.  
         [0050]    [0050]FIG. 6 is a block diagram showing an exemplary functional configuration of the transcoding proxy  10 . As shown in FIG. 6, the transcoding proxy  10  comprises a proxy function unit  11  for intermediating a request (HTTP request) from the web-crawling robot  310  to the site  210  and a response (HTTP response) from the site  210  to the web-crawling robot  310 , a diversity URL database (DB)  12  for registering and holding the information of the site  210  for dynamically creating the content according to the type of client device or URL of content dynamically created (hereinafter referred to as a diversity URL), a link deriving unit  13  as analysis means for deriving a link of the content included in the response sent from the site  210 , a URL conversion unit  14  as editing means for converting a destination URL for a request sent from the web-crawling robot  310 , and a user agent information editing unit  15  for editing the information of user agent in the request.  
         [0051]    The link deriving unit  13 , the URL conversion unit  14 , and the user agent information editing unit  15  may be a virtual software block that is implemented by controlling the CPU  101  with a program expanded in the main memory  103  as shown in FIG. 5. The program for implementing these functions by controlling the CPU  101  may be provided by way of a magnetic disk, an optical disk, a semiconductor memory, or any other storage medium, or distributed via the network. In this embodiment, the program is input via the network interface  106  or the floppy disk drive  109  as shown in FIG. 5, or the CD-ROM drive, not shown, and stored on the hard disk  105 . The program stored on the hard disk  105  is read into the main memory  103 , expanded and executed by the CPU  101  to implement these functions.  
         [0052]    The diversity URL database  12  may be implemented by the main memory, the hard disk  105 , and the CPU  101  controlled by the program, as shown in FIG. 5. Also, the proxy function unit  11  may be implemented by the network interface  106  and the CPU  101  controlled by the program, as shown in FIG. 5.  
         [0053]    In the above configuration, the proxy function unit  11  accepts a request from the web-crawling robot  310 , processes it in the URL conversion unit  14  and the user agent information editing unit  15 , and then sends the processed request to the site  210 . Also, the proxy function unit  11  accepts a response from the site  210 , processes it in the link deriving unit  13 , and sends the processed response to the web-crawling robot  310 .  
         [0054]    The diversity URL database  12  registers the diversity URL that is the URL information of content, as well as the user agent information designating the type of client device to be identified in terms of this diversity URL, namely, corresponding to the content (or site) designated by the diversity URL, and substitute URL individually corresponding to the client device designated by this user agent information.  
         [0055]    The data format of the diversity URL may be a variable length character string. The data format of the user agent information may be a variable length character string, and may have a value (User-Agent value) described in a User-Agent HTTP header of the HTTP request. The data format of the substitute URL may be a variable length character string, and may have the URL of the content (or site) individually corresponding to the client device designated by the user agent information.  
         [0056]    [0056]FIG. 7 is a table showing exemplary information (registered values) registered in the diversity URL database  12 . As shown in FIG. 7, the diversity URL “www.cp_X.com/page — 1.html” corresponds to two client devices, device A and device B, with two substitute URLs “www.cp_X.com/page — 1.html.for.device_A” and “www.cp_X.com/page — 1.html.for.device_B” registered corresponding to the user agent information.  
         [0057]    The above information is acquired in advance from the site  210  or its administrator, and registered. If the diversity URL is newly set up, the information regarding the diversity URL is supplied from the site  210  or its administrator and additionally registered. Also, when the types of corresponding client devices are increased or changed at the site  210  of the diversity URL, the new user agent information is supplied and the registration content is updated.  
         [0058]    Further, control means of the diversity URL database  12  has a link expansion list acquiring function, a URL conversion function, and a user agent information acquiring function as the access functions used by the link deriving unit  13 , the URL conversion unit  14  and the user agent information editing unit  15 , respectively.  
         [0059]    The link expansion list acquiring function is employed for reference by the link deriving unit  13 . If the original URL is passed as the argument, a record with a matched column value is selected from the table as shown in FIG. 7, and the list of corresponding user agent information and substitute URL is returned.  
         [0060]    The URL conversion function is employed for reference by the URL conversion unit  14 . If a substitute URL is passed as the argument, a record with a matched column value is selected from the table as shown in FIG. 7, and the corresponding original URL (diversity URL) is returned.  
         [0061]    The user agent information acquiring function is employed for reference by the user agent information editing unit  15 . If a substitute URL is passed as the argument, a record with a matched column value is selected from the table as shown in FIG. 7, and the corresponding user agent information is returned.  
         [0062]    The link deriving unit  13  analyzes a response sent from the site  210 , detects the diversity URL from the link included in the response, and expands the link into the link (hereinafter referred to as a dummy link) for each corresponding user agent (client device). For example, consider an instance where there is the link to the dynamic content corresponding to two client devices of device A and device B in the web page sent as a response from the site  210 . In this instance, the diversity URL database  12  is retrieved using the link expansion list acquiring function, with the URL that is the link destination of the link as the argument. When the URL of the link is present (or hit) in the diversity URL, the user agent information of device A and device B registered in the diversity URL database  12  and the substitute URL is read out to replace the URL in the link. Thereby, the link is replaced with the dummy link.  
         [0063]    [0063]FIG. 8 is a flowchart for explaining the operation of the link deriving unit  13 . As shown in FIG. 8, if the proxy function unit  11  receives a response from the site  210 , the link deriving unit  13  reads the header part and the body part of the response, and stores them in a work area of the main memory  103  (step  801 ). A determination is made as to whether or not the data type of the body part is text, on the basis of the Content-Type of the read header information (step  802 ).  
         [0064]    If the data type of the body part in the response is text, the link deriving unit  13  checks whether or not the link (hyperlink) is in the body part (web page) (step  803 ). The presence or absence of the link is checked by detecting a tag such as an anchor tag “&lt;a&gt;” or a form tag “&lt;form&gt;” bearing the link. If the link exists, an expansion process for deriving the link into dummy links with substitute URLs is performed (step  804 ). The details of this link expansion process will be described later, with reference to FIG. 9.  
         [0065]    After the deriving process is completed for all the links present in the body part, the link deriving unit  13  rewrites the response received from the site  210  on the basis of the edit result from the expansion process (steps  805  and  806 ). The proxy function unit  11  sends the rewritten response to the web-crawling robot  310 .  
         [0066]    If the data type of the body part in the response is not text, as determined at step  802 , and no link is found in the body part at step  803 , the proxy function unit  11  directly sends the response received by the proxy function unit  11  to the web-crawling robot  310 .  
         [0067]    [0067]FIG. 9 is a flowchart for explaining in detail the deriving process into dummy links at step  804  in FIG. 8. For each link detected at step  803 , the process of FIG. 9 is performed. First, the link deriving unit  13  removes the URL of link destination from the tag such as the anchor tag “&lt;a&gt;” and form tag “&lt;form&gt;” bearing the link, and stores it in a work area of the main memory  103  as shown in FIG. 5 (step  901 ). A determination is made as to whether or not the removed URL is registered in the diversity URL database  12  (step  902 ). For this process, the link expansion list acquiring function is employed.  
         [0068]    When the URL removed from the link is registered in the diversity URL database  12 , the link deriving unit  13  acquires the list of the user agent information of each user agent corresponding to the URL and the substitute URL (step  903 ). The dummy URL is generated on the basis of the substitute URL (step  904 ). The dummy URL is the substitute URL of the corresponding user agent registered in the diversity URL database  12 , with the user agent proper information (screen display size, color tone, and so on) added. Accordingly, since the dummy URL includes the substitute URL, the substitute URL is dealt with as the dummy URL in the following description, unless specifically required.  
         [0069]    The additional information added to the substitute URL may be described by defining an HTTP extension header in the content individually corresponding to the user agent, and acquired by reading it from the extension header. If the substitute URL with user agent proper information included is defined and registered in the diversity URL database  12 , the substitute URL read from the diversity URL database  12  is directly the dummy URL, without need of generating the dummy URL in the link deriving unit  13 .  
         [0070]    After the dummy URLs regarding all the user agents corresponding to the URL (hereinafter referred to as original URL) removed from the link are generated, the link deriving unit  13  replaces the original URL stored in the work area of the main memory  103  with a group of dummy URLs generated, whereby the expansion process into dummy links is ended (steps  905  and  906 ). At this time, the operation returns to the main process (FIG. 8) with the return code set at a return value of “normal end.” The link destination URL described in the response will then be replaced with a group of dummy URLS, as described above (see step  806 ).  
         [0071]    On the other hand, if the URL removed from the link is not registered in the diversity URL database  12  as a result of the processing at step  902 , the operation is directly ended, because it is unnecessary to expand the link. At this time, the operation returns to the main process (FIG. 8) with the return code set at a return value of “unnecessary processing.” 
         [0072]    In the above manner, if the response from the site  210  includes the link to the diversity URL dependent on the type of user agent, this link is expanded into dummy links of corresponding individual user agents (i.e., the original URL (diversity URL) of link destination is replaced with the group of dummy URLs). The response with the expanded links included is sent to the web-crawling robot  310 .  
         [0073]    If the request sent from the web-crawling robot  310  is issued on the basis of the dummy link replaced by the link deriving unit  13 , the URL conversion unit  14  restores the destination of this request (link destination of dummy link) to the original destination. More specifically, the diversity URL database  12  is retrieved by the URL conversion function, with the substitute URL in the dummy URL that is the destination of the request as the argument. The original URL corresponding to the substitute URL and registered in the diversity URL database  12  is read out to replace the destination of the request with the read URL.  
         [0074]    If the request sent from the web-crawling robot  310  is issued on the basis of the dummy link replaced by the link deriving unit  13 , the user agent information editing unit  15  replaces the user agent information described in the header of this request with the user agent information of the user agent corresponding to the dummy link. More specifically, the diversity URL database  12  is retrieved by the user agent information acquiring function, with the substitute URL in the dummy URL that is the destination of the request as the argument. The user agent information corresponding to the substitute URL and registered in the diversity URL database  12  is read out and written into the User-Agent HTTP header.  
         [0075]    [0075]FIG. 10 is a flowchart that illustrates the operation of the URL conversion unit  14  and the user agent information editing unit  15 . As shown in FIG. 10, if the proxy function unit  11  receives a request from the web-crawling robot  310 , the URL conversion unit  14  reads the header part and the body part of the request, and stores them in the work area of the main memory  103  as shown in FIG. 5 (step  1001 ). At this time, the header part of the request is removed, and stored in the work area of the main memory  1003 . A determination is made as to whether or not the URL that is the destination in the header part is registered in the diversity URL database  12  by the URL conversion function (step  1002 ).  
         [0076]    If the URL is the dummy URL expanded by the link deriving unit  13 , the corresponding original URL is returned, because the URL is registered in the diversity URL database  12 . Thus, the URL conversion unit  14  replaces the URL that is the destination in the header part removed from the request stored in the work area of the main memory  103  with the original URL acquired from the diversity URL database  12  (steps  1003  and  1004 ). The process transfers to the user agent information editing unit  15 .  
         [0077]    The user agent information editing unit  15  acquires the user agent information corresponding to the dummy URL (substitute URL) using the user agent information acquiring function. The user agent information (indicating that the web-crawling robot  310  is the user agent) included in the header removed from the request stored in the work area of the main memory  103  is replaced with the user agent information acquired from the diversity URL database  12 , and the operation returns to the URL conversion unit  14  (step  1005 ).  
         [0078]    The URL conversion unit  14  rewrites the header information (destination and user agent information) of the request received from the web-crawling robot  310  and stored in the work area of the main memory  103  on the basis of the result of the URL conversion process and the editing process of user agent information by the user agent information editing unit  15  (step  1006 ). The proxy function unit  11  sends the rewritten request to the site  210 .  
         [0079]    In the above manner, the request from the web-crawling robot  310  disguised as the request from each user agent corresponding to the diversity URL is sent to the site  210 . A response individually corresponding to each user agent is returned from the site  210  and accumulated in the search server  300 . When the response corresponding to the user agent is received from the site  210  and sent to the web-crawling robot  310 , the transcoding proxy  10  embeds the user agent information of the user agent corresponding to the response into the response, employing a meta tag “&lt;meta&gt;”, such as “&lt;meta name=“keywords” content=“devinfo=device_A”&gt;” and “&lt;meta name=“keywords” content=“devinfo=device_B”&gt;”. Thereby, at the search server  300 , the user agent and the response are stored in association. When there is no difference according to the type of user agent (without diversity), the information “&lt;meta name=“keywords” content=“devinfo=ANY”&gt;” is embedded.  
         [0080]    The operation of the transcoding proxy  10  according to this embodiment is now described below by way of a specific example.  
         [0081]    [0081]FIG. 11 shows an exemplary configuration of the contents collected in this embodiment. Suppose the content is composed of two web pages (HTML file), page — 1.html and page — 2.html, as shown in FIG. 11. In this case, page — 1.html has a link to page — 2.html, and page — 2.html is a web page dynamically created corresponding to two types of user agents of device A and device B.  
         [0082]    [0082]FIG. 12 is an exemplary diagram for explaining the process in which the web-crawling robot  310  collects the content information as shown in FIG. 11. Suppose that the web-crawling robot  310  first issues an acquisition request (request 1) for page — 1.html to the site  210 , as shown in FIG. 12. Request 1 is sent via the transcoding proxy  10  to the site  210 , and the site  210  returns a response 1 to the request 1. The substance of response 1 is page — 1.html.  
         [0083]    The transcoding proxy  10  processes page — 1.html, and because there is a link to page — 2.html and because the content of page — 2.html depends on the type of user agent (i.e., the URL for page — 2.html is the diversity URL), the link deriving unit  13  performs the link expansion process. Thereby, response 1 is converted into response 1′ containing the web page having the link to page — 2.html corresponding to device A (page — 2_for_A.html) and the link to page — 2.html corresponding to device B (page — 2_for_B.html), and sent to the web-crawling robot  310 .  
         [0084]    The web-crawling robot  310  issues an acquisition request for page — 2_for_A.html and page — 2_for_B.html in succession, because the web page that is the substance of the received response 1′ has two links to page — 2_for_A.html and page — 2_for_B.html.  
         [0085]    Suppose now that an acquisition request (request 2) for page — 2_for_A.html is issued. The transcoding proxy  10  restores the URL that is the destination of request 2 to the original URL, using the URL conversion unit  14  and the user agent information editing unit  15 , and converts the user agent value of the HTTP header to the user agent value indicating device A. Thereby, the request 2 is sent  210  by disguising it as the request issued from device A (request 2′). The site  210  returns a response 2′ containing the content page — 2.html for device A upon this request 2′.  
         [0086]    In the example of FIG. 11, the link expansion process for the response 2′ is not performed in the transcoding proxy  10 , because page — 2.html includes no link to the diversity URL, whereby the response 2′ with user agent information for indicating the response corresponding to device A added in meta tag is sent to the web-crawling robot  310 .  
         [0087]    Then, the web-crawling robot  310  issues an acquisition request for page — 2_for_B.html (request 3), and through the same process, a response 3′ corresponding to device B is returned to the web-crawling robot  310 .  
         [0088]    [0088]FIG. 13 is an exemplary diagram regarding a process for making the link expansion to a response from the site  210  to the web-crawling robot  310 . As shown in FIG. 13, the proxy function unit  11  of the transcoding proxy  10  receives a response sent from the site  210  ( 1 ), then sends a receiving notice to the link deriving unit  13  ( 2 ), and acquires the response from the link deriving unit  13  ( 3 ). The link in the body part of the response is retrieved ( 4 ). The obtained link is held in the work area of the main memory  103  as shown in FIG. 5.  
         [0089]    The link deriving unit  13  searches the diversity URL database  12  with the URL (original URL) at the link destination of the link present in the body part of the response to acquire the substitute URL for each user agent corresponding to the original URL ( 5 ). The link expansion process is performed for generating the dummy URL including the acquired substitute URL and replacing the original URL held in the work area of the main memory  103  with the substitute URL ( 6 ). At this time, when there is no link to the content returning the response individually corresponding to the type of user agent (there is only the link to the content returning the uniform response irrespective of the type of user agent), the substitute URL is not acquired, and the link expansion process is not performed, because the corresponding URL is not registered in the diversity URL database  12 .  
         [0090]    Finally, the link deriving unit  13  rewrites the URL (original URL) described in the body part of the response into the group of dummy links replaced in the work area of the main memory  103  ( 7 ), and returns the edited response to the proxy function unit  11  ( 8 ). The proxy function unit  11  sends the edited response to the web-crawling robot  310 .  
         [0091]    [0091]FIG. 14 is a diagram regarding a process for making a request from the web-crawling robot  310  to the site  210 . As shown in FIG. 14, the proxy function unit  11  of the transcoding proxy  10  receives a response sent from the web-crawling robot  310  ( 1 ), then sends a receiving notice to the URL conversion unit  14  ( 2 ), and acquires a request from the URL conversion unit  14  ( 3 ). The diversity URL database  12  is retrieved with the URL at the destination of the request as the argument ( 4 ). If the URL at the destination is the dummy URL generated in the previous link expansion process, the corresponding original URL is returned, because the substitute URL is registered in the diversity URL database  12 .  
         [0092]    If the original URL is returned from the diversity URL database  12 , the URL at the destination is converted into the original URL in the work area of the main memory  103  ( 5 ). The operation transfers to the user agent information editing unit  15  ( 6 ).  
         [0093]    The user agent information editing unit  15  retrieves the diversity URL database  12  with the URL at the destination of the request as the argument ( 7 ). An editing process is performed for acquiring the user agent information of the corresponding user agent and converting the user agent information included in the header information of the request into the acquired user agent information on the work area of the main memory  103  ( 8 ).  
         [0094]    Thereafter, the URL conversion unit  14  reflects the conversion of the URL and the conversion of the user agent information in the work area of the main memory  103  to the header part of the request received from the web-crawling robot  310  ( 9 ), and returns the processed request to the proxy function unit  11  ( 10 ). This processed request is sent from the proxy function unit  11  to the site  210 .  
         [0095]    Through the above operation, the web-crawling robot  310  acquires the response according to the type of each corresponding user agent from the site  210 , which site responds with different substance according to the type of user agent. The search server (search site)  300  having the web-crawling robot  310  creates the index information used for searching from the content collected in this manner and registers it in the database. The index information includes the information indicating the type of user agent corresponding to the location information of content and the information of text in the content.  
         [0096]    [0096]FIG. 15 is an exemplary block diagram schematically showing a suitable configuration of the search server  300 . As shown in FIG. 15, the search server  300  comprises the web-crawling robot  310 , the database  320  for storing the index information for searching information, and the search engine  330  for retrieving the database  320 . Transmitter-receiver means for accepting a search request from the client device (user agent) via the network and returning the search result through the search engine  330  is provided, although not explicitly shown in the figure. The database  320  stores the index information created from the contents collected by the web-crawling robot  310 , as described above. In this embodiment, the transcoding proxy  10  embeds the user agent information in the response from the site  210 , employing meta tag “&lt;meta&gt;”, whereby the index information may include the information indicating the association of the index information with the user agent.  
         [0097]    [0097]FIG. 16 is a flowchart for explaining the operation of the search engine  330  when accepting a search request from the predetermined client device (user agent). The predetermined client device sends a search request to the search server  300 . The HTTP header or extension header of this search request stores the search term (keyword) and the user agent information.  
         [0098]    As shown in FIG. 16, the search request from the client device is received and read (step  1601 ). Then, the search engine  330  removes the search term (keyword) in the input search request and the user agent information (step  1602 ). The database  320  is searched by extracting the content under the constraint conditions of this information (step  1603 ). That is, the database  320  is retrieved in the search term by extracting the content with character string “devinfo=user agent information” or “devinfo=ANY” included in the keywords information of the meta tag.  
         [0099]    Then, the search engine  330  creates a response page describing the search result in a predetermined format (step  1604 ), and returns the response page to the client device making the search request (step  1605 ).  
         [0100]    In the above manner, the client device obtains the search result suitable for itself from the search server  300 . This search result is obtained by extracting the content from among the contents retrievable by the search server  300 , and therefore includes the information of content created appropriately for each device. Thus, as described above, the invention enables a site to acquire information on contents classified by type of corresponding terminal if the site dynamically creates the content and returns an individual response according to the type of client device, when a web-crawling robot collects information.