Abstract:
The access method comprises the following steps:
       i) receiving a notification indicating the presence of at least one digital document available on the network, said notification comprising at least one executable command adapted to detect whether the recipient client device comprises a local application capable of processing the digital document,   ii) executing the command or commands in order to detect the local application, and   iii) in case of positive detection, accessing the digital document from a local server whereas in case of negative detection, accessing the document from the address of a remote server.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to accessing and/or sharing a digital document available in a communication network linking client devices together, said method utilizing a notification indicating the presence of a digital document available on the network, the notification being suitable for adaptation and for exploiting the presence or not of a local application able to process the digital document. 
     It has general application in the processing of digital documents available in a communication network, in particular communication networks of peer-to-peer type, designated hereinafter by the acronym P2P. 
     P2P communication systems have emerged in recent years constituting a revolution in file sharing in comparison with the conventional client-server model. In P2P systems, each machine (also termed node or peer) constituting the communication network acts as a client device as well as a server device. Thus, in a P2P network, the apparatuses put resources in common according to a philosophy of sharing as coequals, each machine of a P2P network acting both as client and as server. Such networks are thus distinguished from conventional client-server networks in which the resources are archived in a central server device. 
     Currently, the distribution of data relies increasingly on P2P networks due to their low-cost installation, the presence of very numerous computers connected to the networks, and due to the development of broadband connections. 
     However, P2P networks are unstable. This is because client devices (and consequently server devices) connect and disconnect periodically to the network, thus rendering the presence of data highly unpredictable. Furthermore, the addresses of client and/or server devices are unpredictable and liable to be different at each connection. 
     Due to their specificity, P2P systems generally imply the utilization of a local, dedicated client application, also termed a P2P local application. Such a P2P local application ensures the sharing of digital content, as well as searching and accessing the digital content available on P2P networks. 
     For example, the P2P local application may provide a notification mechanism based on the exchange of messages according to a proprietary protocol in order to enable a client device to notify one or more persons that it has just shared new digital contents on the network. 
     The P2P local application may also utilize electronic mail as a main mechanism for notification or as a supplement to the proprietary notification system. In this case, the electronic mail may possibly contain one or more specific files as attachments which may be interpreted by the P2P local application at the recipient or recipients. 
     P2P systems are also known which enable users not having any P2P local application to access the content on the network with the aid of Internet access tools that are more conventional and widespread such as browsers or Internet navigators. 
     In such systems, certain specific server devices or client devices in the network act as server devices playing the role of gateway between the Internet access tool (browser, explorer, navigator) and the P2P network. These machines may be viewed as proxy devices which take on the task of retrieving the resource sought on the P2P network for the Internet tool. In these systems, email is utilized conventionally as a notification mechanism. The email may then contain a page in markup language or a link (also termed a URL from “Uniform Ressource Locator”) to a page enabling the recipient user to access the resources. 
     Thus, in a P2P system, a user may utilize a P2P local application to share digital content over the network, and to browse and access the content available on the P2P network. 
     The user not having the P2P local application or the user not wishing to utilize the interface provided may also utilize tools capable of viewing pages in markup language to access the digital content (Web explorer, email reader, or any other application capable of displaying pages in markup language). 
     For example, the user may share collections of digital content with a group of persons, it being possible for those persons to have the P2P local application or not. 
     The Applicant set itself the problem of providing a method enabling recipient client devices to be notified in a uniform manner without having to know a priori whether said recipients posses a P2P local application dedicated to the processing of digital documents. 
     SUMMARY OF THE INVENTION 
     A solution to this problem is precisely what the present invention provides. 
     It relates to a method of accessing at least one digital document available on a communication network linking client devices together, said accessing method being implemented on a recipient client device. 
     According to a general definition of the invention, the method comprises the following steps: 
     i) receiving a notification indicating the presence of at least one digital document available on the network, said notification comprising at least one executable command adapted to detect whether the recipient client device comprises a local application capable of processing the digital document; 
     ii) executing the command or commands in order to detect the presence and activation of the local application; and 
     iii) in case a local application is present and active, accessing the digital document from a local server whereas in case of absence or inactivity of the local application, accessing the document from a remote server. 
     Thus, the method uniformly notifies the users of a network who posses or do not posses the local application. More particularly, the method optimizes the utilization of the network via the notification by seeking to enable the utilization of the local application to view digital documents as soon as that application is available with a user while remaining compatible with those who do not posses that local application. 
     Thus, provision is made to modify the information contained in the notification at the time of its viewing depending on the presence or not of the local application with the recipient. 
     In practice, the notification further comprises a page in markup language containing at least one identifier designating the digital document, and a remote address designating a remote server. 
     According to one embodiment, the method further comprises, at the issue of step ii) and prior to step iii), the step iia) in which, in case a local application is present and inactive, provision is made to proceed with the activation of the local application further to an authorization by the user of the recipient client device granted in response to a chosen executable command. 
     As a variant, at the issue of step ii) and prior to step iii), the method further comprises the step iib) in which, in case a local application is present and inactive, provision is made to proceed automatically with the activation of the local application in accordance with a chosen executable command. 
     According to another embodiment, the method further comprises, after step iii), the step iv) in which, in case a local application is present and active, provision is made to verify the presence of the document on a local server, and in case of negative verification to search for said document on the network, to download it in case of positive search, and to save it locally before serving it in response to the request for access. 
     According to another embodiment, in case a local application is present and active, provision is made to locally adapt the page in markup language so as to access the document from the address of a local server. In practice, the adaptation of the page comprises the setting of a linking variable in markup language to the address of a local server. 
     According to still another embodiment, in case a local application is absent or inactive, provision is made to locally adapt the page in markup language so as to access the document from the address of a remote server. In practice, the adaptation of the page comprises the setting of a linking variable in markup language to the address of a remote server. 
     In practice, the communication network is of peer-to-peer type, centralized, decentralized, or hybrid. 
     For example the page may be written in markup language of HTML type or similar, or the commands included in the page in markup language calling on a local program of activeX type or similar, adapted to determine the presence and activation of a local server, as well as to retrieve the configuration parameters of said local server. 
     For example, the executable command or commands may be of Script program type such as Java Script or VB Script, the said command or commands being embedded in the page thus notified. 
     For example, the local address designating a local server may be determined by the Script program adapted to retrieve the configuration parameters of said local server. 
     The command further comprises a function adapted to link a local or remote address enabling the document to be accessed. 
     In practice, the page is notified as an attachment with an email. 
     According to a variant form, the page is downloaded onto a chosen remote server and a reference to that page is sent to any recipient to be notified, the reference of the page being, for example, of URL type, included in an email. 
     The present invention also relates to a method of sharing a digital document in a communication network linking client devices together, said method being implemented on a sending client device. 
     According to another aspect of the invention, the method comprises the following step:
         sending to at least one recipient client device a notification indicating the presence of at least one digital document available on the network, said notification comprising at least one executable command adapted to detect whether the recipient client device comprises a local application capable of processing the digital document, and in case a local application is present and active, to access the document from the address of a local server otherwise to access the document from the address of a remote server.       

     The present invention also relates to a device for accessing at least one digital document adapted to implement the accessing method according to the invention. 
     Similarly, the present invention also relates to a device for sharing a digital document adapted to implement the method of sharing mentioned above. 
     The present invention also relates to an information carrier readable by a computer system, possibly wholly or partly removable, in particular a CD-ROM or magnetic medium, such as a hard disk or a diskette, or a transmissible medium, such as an electrical or optical signal, characterized in that it comprises instructions of a computer program enabling the implementation of the method according to the invention, when the program is loaded and run by a computer system. 
     Finally, the present invention also relates to a computer program stored on an information carrier, said program comprising instructions enabling the implementation of a processing method in accordance with the invention, when that program is loaded and run by a computer system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will appear in the light of the following detailed description and drawings in which: 
         FIG. 1  is a diagram of the essential elements of a recipient client device adapted to implement the accessing method according to the invention; 
         FIG. 2  is a diagram of a communication network linking client devices together according to the invention; 
         FIG. 3  is a flowchart illustrating the steps relative to the viewing of a page in markup language according to the invention; 
         FIG. 4  is a flowchart illustrating the steps relative to the verification of the activation of the local application according to the invention; and 
         FIG. 5  is a flowchart illustrating the behavior of a local server according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , an apparatus implementing the invention is for example a microcomputer  10  or a workstation connected to different peripherals such as a digital moving image camera  11  (or a scanner, or any other means of acquiring or storing digital documents such as images) connected to an input/output card (not shown) and supplying multimedia data to the apparatus. 
     The apparatus  10  comprises a communication bus  101  to which there are connected several elements such as:
         a central processing unit  102  (microprocessor, denoted CPU in  FIG. 1 );   a read only memory  103  able to contain programs according to the invention;   a random access memory  104 , which, after powering up, contains the executable code of the method according to the invention as well as registers adapted to record variables and parameters necessary for the implementation of the invention;   a screen  105  for displaying the data and/or serving as a graphical interface with the user, who will be able to interact with the programs according to the invention, using a keyboard  106  or any other means such as a pointing device, for example a mouse  107  or an optical stylus (not shown);   a hard disk  108  able to contain the programs according to the invention as well as data utilized or produced when the invention is implemented;   a disk drive  109  adapted to receive a diskette  12  and to read or write thereon data processed or to be processed according to the invention; and   a communication interface  110  connected to a communication network  13 , the interface being adapted to transmit and receive data.       

     In the case of audio data, the apparatus  10  may further comprise an input/output card (not shown) connected to a microphone  14 . 
     The communication bus  101  affords communication and interoperability between the different elements included in the apparatus  10  or connected to it. The representation of the bus is non-limiting and, in particular, the central processing is capable of communicating instructions to any element of the apparatus  10  directly or by the intermediary of another element of the apparatus  10 . 
     The diskettes  12  can be replaced by any information carrier such as a compact disc (CD-ROM) rewritable or not, a ZIP disk or a memory card. 
     Generally, an information storage means, which can be read by a micro-computer or microprocessor, integrated or not into the device, and which may possibly be removable, is adapted to store one or more programs whose execution permits the implementation of the method according to the invention 
     The executable code enabling the apparatus to implement the invention, may equally well be stored in read only memory  103 , on the hard disk  108  or on a removable digital medium such as a diskette  12  as described earlier. 
     According to a variant, the executable code of the programs may be received by the intermediary of the communication network  13 , via the interface  110 , to be stored in one of the storage means of the apparatus  10  before being run (such as the hard disk  108 ). 
     The central processing unit  102  controls and directs the execution of the instructions or portions of software code of the program or programs according to the invention, those instructions being stored in one of the aforementioned storage means. 
     On powering up, the program or programs which are stored in a non-volatile memory, for example the hard disk  108  or the read-only memory  103 , are transferred into the random-access memory  104  (RAM), which then contains the executable code of the program or programs according to the invention, as well as registers for storing the variables and parameters necessary for implementation of the invention. 
     It should be noted that the apparatus comprising the device according to the invention can also be a programmed apparatus. This apparatus then contains the code of the computer program or programs for example fixed in an application specific integrated circuit (ASIC). 
     With reference to  FIG. 2 , a communication network  13  connects together several client devices or terminals, individualized as client 1   21 , client 2   22 , and client 3   23 . Each client device may be connected to the network  13  by different communication means such as broadband or narrow band communication means (xDSL modem, PSTN or cable). The network  13  may be constituted equally well on top of the Internet network as on top of a Local Area Network (LAN) or by a combination of both. 
     The terminals of the client devices fall into two distinct categories. There are either terminals provided with the dedicated “peer-to-peer” P2P application (client 2  and client 1 ) or terminals not provided with that dedicated “peer-to-peer” P2P application (client 3 ). 
     The terminals provided with the dedicated “peer-to-peer” P2P application form between them a communication network of “peer-to-peer” P2P type through the communication network  13  and according to one of the topologies known to the person skilled in the art (centralized, decentralized with or without central server “superpeers” or else hybrid). 
     The “peer-to-peer” P2P application comprises at least one server module bearing the reference  218  in the client device  21  or the reference  228  in the client device  22 . The P2P application further comprises a storage means or cache  217 ,  226 . 
     The server module  218  or  228  is given the task of responding to the requests for access to the “peer-to-peer” resources. The requests may equally well come from remote applications as applications present on the same machine as the server. 
     The requests may equally well be received according to a proprietary protocol of the “peer-to-peer” application as according to the HTTP (the HyperText Transfer Protocol) commonly utilized on the Internet 
     The storage means  217 ,  226  contains digital content shared on the “peer-to-peer” network with the aid of the server module  218 ,  228 . The “peer-to-peer” application may also be supplemented by a P2P dedicated local client local application ( 219 ,  229 ) providing a interface with the user enabling him to search, access, view and share digital content on the “peer-to-peer” network. 
     All the terminals, whether provided or not with the dedicated “peer-to-peer” application, may also utilize tools ( 227 ,  237 ) capable of viewing pages in HTML type markup language to access digital content with the help of the HTTP communication protocol. 
     One or more specific proxy/gateway servers  24  may also be connected to the network  13 , these servers offering an entry point to the “peer-to-peer” network for clients not having dedicated “peer-to-peer” clients and utilizing the HTTP communication protocol. 
     When they receive a request for a resource of the “peer-to-peer” network, the proxy servers  24  determine one or more machines of the “peer-to-peer” network liable to have the requested resource and take on the task either of redirecting the requester to one of those machines, or of retrieving the resource from one of those machines on behalf of the requester to then serve it to the requester as a proxy type server. 
     It should be noted that this role of proxy/gateway server may also be fulfilled by the client devices themselves if they have a dedicated “peer-to-peer” application, such as the client devices  1  and  2  respectively numbered  21  and  22 . 
     According to the invention, if the user connected to machine  21  wishes to share a new collection of digital content composed of images individualized as image 1 , image 2  and image 3  present on its disk  217  with clients  22  and  23 , he utilizes the P2P local application  219  to create and share a new collection composed of those three images. 
     During sharing, the P2P local application  219  associates a unique identifier Image 1  ID, Image 2  ID, Image 3  ID with each image. Tools well known to the person skilled in the art make it possible to generate identifiers with an infinitesimal probability of duplication. 
     After the actual sharing operation that is specific to the “peer-to-peer” application, the P2P local application  219  generates a page  25  in HTML markup language describing the new collection in order to notify clients  22  and  23  that a new collection of digital content is available on the network. This HTML page contains at least some scripts  252  such as javaScripts and a reference for each of the identifiers of newly shared digital content  253 . 
     Once the HTML page  25  has been generated, the user may send that page to all the persons which he wishes to notify of the existence of new shared digital content (on our example client 2  and client 3 ). 
     In the preferred embodiment, the user sends the HTML page  25  by making it an attachment to an email. 
     In another embodiment, the user downloads the HTML page  25  onto a server such as server  24 . Furthermore, the user sends a reference designating that HTML page on said server to all the persons he wishes to notify, for example in the form of a URL included in an email. The recipients download the HTML page  25  from the server  24  using the reference (the said URL) received as notification. 
     The user may equally well use any other means making it possible to transmit the HTML page to recipients (for example using a “peer-to-peer” file exchange system, by physically mailing a diskette containing the HTML, etc.). 
     When the HTML page  25  is received and displayed by the recipients using applications  227  and  237 , that is to say an Internet navigator, an email reader or any other application capable of interpreting and displaying an HTML page, the content of the page is interpreted and the executable codes (scripts) contained in the page are executed. 
     A first code is given the task of determining whether the dedicated “peer-to-peer” P2P local application is installed. 
     If the dedicated application is installed, the first code retrieves, using a second code external to the HTML page (e.g. activeX), configuration information on the “peer-to-peer” application such as the numbers associated with network ports utilized by the application. Next, the first code initializes variables which are utilized by a third code embedded in the HTML page  25  and given the task of generating the URL addresses to utilize for accessing the digital contents. 
     The third code is invoked on interpretation of the HTML page for each of the references to the shared digital contents. If the “peer-to-peer” local server  228  has been detected by the first code as being installed and active, the third code returns HTML code of which the URLs are directed to the “peer-to-peer” local server (case C 1  for client  2  in  FIG. 2 ). The URLs may be of the form http://localhost:80/RUID where RUID represents the unique identifier of the shared resource. 
     If the “peer-to-peer” local server  228  is not present on machine  22  or is not active, the third code sends back HTML code of which the URLs are directed to a predefined remote server providing a gateway between http web requests and the “peer-to-peer” network such as the “peer-to-peer” proxy/gateway web/server  24  (case of client  3  and case C 2  for client  2  in  FIG. 2 ). 
     The URLs sent back may be of the form http://www.server.com/RUID where www.server.com represents the web address of server  24  and RUID represents the unique identifier of the shared resource. 
     The invention thus make it possible to adapt the content of the notification (HTML page  25 ) depending on whether the recipient has the “peer-to-peer” application or not. 
     In our example, device client 3   23  does not have the “peer-to-peer” application. In its case, all the accesses to the shared digital contents are thus directed to the proxy server  24 . 
     On the other hand, for device client 2   22  the accesses to digital contents are directed to its “peer-to-peer” server  228  if it is active (case Cl) and to the proxy server  24  if it is inactive (case C 2 ). 
     The advantages of utilizing the “peer-to-peer” server as soon as it is available are in particular the fact of not accessing the network if the data are already present in the cache of the “peer-to-peer” server. In addition, if the digital contents are accessed through the “peer-to-peer” local server, said contents are then present in the cache of the server and thus may be served to remote machines in return. The number of machines in the “peer-to-peer” network able to serve a given digital content is thereby increased. As the machines may be disconnected at any moment, the probability of finding a given digital content on the network at any instant is thereby increased. 
     With reference to  FIG. 3 , a flowchart has been represented illustrating the behavior of the script given the task of determining whether a “peer-to-peer” local server is present and active on the machine. 
     This script is integrated into the HTML page  25 , either in the form of a script  252  bounded by HTML tags &lt;SCRIPT LANGUAGE=###&gt; and &lt;/SCRIPT&gt; where ### indicates the language utilized, or in the form of a reference to an external file. 
     The script is interpreted and executed at each display of the HTML page. 
     At step S 302 , the script commences by verifying whether the “peer-to-peer” application is installed or not on the machine. For this, it seeks to detect the presence of an activeX program or of an extension module (plug-in) forming part of the “peer-to-peer” application. 
     For example, if the program to detect is an activeX, it may invoke the function defined by the following VBscript program: 
     
       
         
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 &lt;SCRIPT LANGUAGE=“VBscript”&gt; 
               
               
                   
                 &lt;!-- 
               
               
                   
                 Function detectActiveXControl(activeXControlName) 
               
               
                   
                   on error resume next 
               
               
                   
                   detectActiveXControl = False 
               
               
                   
                   detectActiveXControl = 
               
               
                   
                   IsObject(CreateObject(activeXControlName)) 
               
               
                   
                 End Function 
               
               
                   
                 rem --&gt; 
               
               
                   
                 &lt;/SCRIPT&gt; 
               
               
                   
                   
               
             
          
         
       
     
     This function detectActiveXControl takes as parameter the name of the activeX and gives True if the activeX is present on the machine and False otherwise. 
     At step S 303 , if the application has been detected as not present on the machine, the algorithm goes to step S 308  and sets a variable indicating that in the following processing of the HTML page use must be made of the URLs directed to the remote server  24 . 
     If, on the contrary, the P2P application has been detected, the script determines at step S 304  whether the “peer-to-peer” local server  228  is currently active (that is to say in course of execution) or not. For this, it utilizes the activeX program detected at the preceding step to retrieve the current configuration of the “peer-to-peer” server  228  by consulting either the registers or a configuration file. 
     For example, the activeX program retrieves the number of the network port on which the server  228  is listening. If the latter is inactive, the port has the value zero. If the value is different from zero, at step S 309 , it sets a variable containing the port number on which the server  228  is listening. 
     At step S 310 , the script sets a variable indicating that in the following processing of the HTML page  25  use must be made of the URL addresses directed to the local server  228  to access the digital contents. 
     For example if GetRegValue is a function of the activeX MpActiveXVB enabling the register to be accessed, the following program may be utilized to determine whether the local server is active or not and retrieve its port number (step S 304  and S 309 ). 
     
       
         
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 &lt;SCRIPT LANGUAGE=“JavaScript”&gt; 
               
               
                   
                 &lt;!-- 
               
               
                   
                 var IsLocalServerActive = false; 
               
               
                   
                 var LocalServerPort = 80; 
               
               
                   
                 function CheckLocalServer( ) 
               
               
                   
                 { 
               
               
                   
                  LocalServerPort = 
               
               
                   
                 MpActiveXVB.GetRegValue(“SOFTWARE\\LocalServer\\Config\\ 
               
               
                   
                 ListenPort}”); 
               
               
                   
                  if(LocalServerPort != 0) 
               
               
                   
                  { 
               
               
                   
                   return true; 
               
               
                   
                  } 
               
               
                   
                  return false; 
               
               
                   
                 } 
               
               
                   
                 IsLocalServerActive = CheckLocalServer( ); 
               
               
                   
                 // --&gt; 
               
               
                   
                 &lt;/SCRIPT&gt; 
               
               
                   
                   
               
             
          
         
       
     
     If server  228  is detected as inactive at step S 304 , the program may invite the user to launch the “peer-to-peer” local server  228  by opening a dialog box using a function of the activeX. 
     If the user accepts the proposal, a function of the activeX is invoked to launch the local server at step S 307 . 
     At step S 311  continuation of the interpretation of the HTML page  25  is proceeded with. 
     With reference to  FIG. 4 , each time the HTML page  25  is analyzed by an application such as an Internet navigator or an email reader ( 227 ,  237 ), a JavaScript function embedded in the page is invoked for each reference to a digital content in order to give the URL address to use to access said digital content. 
     The invocation of that function in the HTML page may take the following form:
 
&lt;SCRIPT LANGUAGE=“JavaScript”&gt;GetRessourceAddress(‘abcde23404-3143492ef-23232’, ‘blue_mountain.jpg’); &lt;/SCRIPT&gt;
 
     The tag &lt;SCRIPT LANGUAGE=###&gt; marks the beginning of a code to execute in the HTML page, where the value ### mentions the nature of the language utilized (JavaScript or VBScript for example). The tag &lt;/SCRIPT&gt; indicates the end of the code to execute. 
     GetRessourceAddress here corresponds to the name of the JavaScript function to invoke. This function must be defined beforehand, either in an external file the name of which terminates with the extension “.js” itself referenced in the HTML page, or directly at the beginning of the HTML page (that is to say in the header bounded by the tags &lt;HEAD&gt; and &lt;/HEAD&gt; in a section of JavaScript code bounded by the tags &lt;SCRIPT LANGUAGE=“JavaScript”&gt; and &lt;/SCRIPT&gt;). 
     In the first case, if the name of the server hosting the script is “www.server.com” and the file containing the definition of the function is called “mp.js” and is found in the “script” folder on the server, the command including the “mp.js” file in the HTML page is:
 
&lt;SCRIPT LANGUAGE=“JavaScript”src=“http://www.server.com/script/mp.js”&gt;&lt;/SCRIPT&gt;
 
       FIG. 4  describes the behavior of the JavaScript function GetRessourceAddress given the task of giving the URL address. 
     The corresponding code in JavaScript may be the following: 
     
       
         
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 function GetRessourceAddress(resID, title) 
               
               
                   
                  { 
               
               
                   
                  if(isLocalServerActif == false) 
               
               
                   
                  { 
               
               
                   
                   document.write(“&lt;A HREF=http://www.server.com/”); 
               
               
                   
                   document.write(resID); 
               
               
                   
                  } 
               
               
                   
                  else 
               
               
                   
                  { 
               
               
                   
                   document.write(“&lt;A HREF=http://localhost:”); 
               
               
                   
                   document.write(localServerHTTPPort); 
               
               
                   
                   document.write(“/”); 
               
               
                   
                   document.write(resID); 
               
               
                   
                  } 
               
               
                   
                  document.write(“&gt;”); 
               
               
                   
                  document.write(title); 
               
               
                   
                  document.write(“&lt;/A&gt;”); 
               
               
                   
                 } 
               
               
                   
                   
               
             
          
         
       
     
     The keyword function indicates the creation of a new function the name of which is GetRessourceAddress here and which has two variables as parameters, resID and title. JavaScript has a command named document.write(#) making it possible to display information by passing that information denoted here by hash to the program in course of interpreting the HTML page. The information passed must thus be in HTML format to be comprehensible by the interpreter. 
     The words isLocalServerActif and localServerHTTPPort represent JavaScript variables initialized beforehand ( FIG. 3 ). The first variable indicates a “peer-to-peer” local server is currently installed and active on the machine and the second variable indicates the port number on which the “peer-to-peer” local server awaits. 
     According to the invention the algorithm is thus the following: 
     The JavaScript function here denoted GetRessourceAddress having as parameters at least the unique identifier of the resource denoted resID is invoked (step S 401 ) for each of the references to the resources in the HTML page  25 . 
     At step S 402 , the function verifies whether a “peer-to-peer” local server has been detected by the algorithm of  FIG. 3  by verifying the value of a variable denoted here by isLocalServerActif. 
     At step S 403 , if the variable indicates that there is no “peer-to-peer” local server currently active (the value of the variable is false), then at step S 404  the function gives a URL enabling the resource to be accessed via a predefined address corresponding to a server  24  of proxy/gateway type of which the name would for example be www.server.com. 
     On the basis of the code of the JavaScript function and the example of invocation described earlier, the HTML code given by the function is the following:
 
&lt;A HREF=http://www.server.com/abcde23404-3143492ef-23232&gt;‘blue_mountain.jpg’&lt;/A&gt;
 
     This code represents a hypertext link having the name blue_mountain.jpg and linking to the address http://www.server.com/abcde23404-3143492ef-23232. 
     At step S 403 , if the variable indicates that there is a “peer-to-peer” local server active on the machine (the value of the variable is true), then at step S 405  the function gives a URL enabling the resource to be accessed via the local server which here has the role of proxy ( FIG. 5 ). The HTML code given by the function would then be:
 
&lt;A HREF=http://localhost:90/abcde23404-3143492ef-23232&gt;‘blue_mountain.jpg’&lt;/A&gt;
 
assuming the variable localServerHTTPPort has the value 90.
 
     In another variant, rather than invoking the JavaScript function GetRessourceAddress for each of the references to a digital content, these references may be written in the form of a relative URL. An example of HTML code for a reference may then have the following form:
 
&lt;A HREF=abcde23404-3143492ef-23232&gt;‘blue_mountain.jpg’&lt;/A&gt;
 
     Repeated invocation of the JavaScript function GetRessourceAddress for each of the references to a digital content is then advantageously replaced by a single invocation to a JavaScript routine given the task of defining a tag &lt;BASE&gt; in the header of the HTML page  25 . This tag defines an absolute URL utilized as basic URL to resolve the relative URLs. 
     The JavaScript function gives a tag &lt;BASE&gt; linking to a server  24  of proxy/gateway type if there is no “peer-to-peer” local server active on the machine (the variable isLocalServerActif has the value false). The HTML code given by the function is then:
 
&lt;BASE HREF=http://www.server.com/&gt;
 
     The JavaScript function gives a tag &lt;BASE&gt; linking to a local server  228  if there is an active “peer-to-peer” local server on the machine (the variable isLocalServerActif has the value true). The HTML code given by the function is then:
 
&lt;BASE HREF=http://localhost:90/&gt;
 
assuming the variable localServerHTTPPort has the value  90 .
 
     With reference to  FIG. 5 , the behavior of the local servers  228  and  218  has been described. 
     According to the invention when the “peer-to-peer” local server receives a request for a digital content R (S 511 ) it determines at step S 512  whether the request comes from a remote application (present on another machine of the communication network) or whether the request comes from a local application (running on the same machine as the server). It determines this information by examining the IP address of the requester and by comparing it to each of its own IP addresses. If two addresses are identical or if the address of the requester is 127.0.0.1 (loopback address), this means that the requester is local, otherwise it is a remote requester. 
     If the requester is local, the server goes to step S 513  and verifies whether the data R sought is not locally present on the disk. If the data is present locally, it is sent to the requester (step S 517 ). If the data is not present locally the server performs a search for the resource on the “peer-to-peer” network using techniques known to the person skilled in the art (step S 514 ). At step S 515 , if the data is found on the network then the server downloads the data R at step S 516 , saves it locally in its cache on the disk and sends it back to the requester at step S 517 . In the opposite case, the server sends back an error to the requester at step S 518  to indicate to him that the data is not available. 
     If the requester is remote, at step S 519  the server verifies whether the resource is available locally on its disk. 
     If the data is available, it is sent back to the requester at step S 520 . In the opposite case, at step S 521  it varifies whether the request is a WEB request coming for example from an Internet navigator (in the form of a URL http://y/x where [x] is the access path to the resource on the machine identified by [y], or else in the form of a particular header in the request) or whether it is a request according to a proprietary “peer-to-peer” protocol. 
     If it is a WEB request, the server then carries out a search for the data on the “peer-to-peer” network at step S 522 . The proxy/gateway behavior of machine  24  is again found here. 
     At step S 523 , if the resource is localized in the “peer-to-peer” network, the server does not download the resource but on the contrary at step S 524  re-directs the requester to the machine having the resource sought using a forwarding order of which a simple form with the HTTP protocol would be:
         HTTP/1.1 302 See other URI   Location: http://nnn/zzz       

     The first key word http/1.1 makes it possible to indicate the type and version of the protocol  302  is a particular error value indicating that the resource is temporarily not available on the server. A comment which may be displayed follows that error code. Location: is the second key word indicating to the Internet navigator to redirect itself to another URI. [nnn] is the address of the machine to contact to obtain the resource and [zzz] is the access path to the resource on the machine [nnn]. 
     At step S 523 , if the resource is not located on the “peer-to-peer” network, at step S 525  the server redirects the requester to a predetermined machine using a forwarding order similar to the preceding one. That predetermined machine is given the task of dealing with the case in which the requested resource is not available by sending back for example a predetermined response inviting the user to renew its request later for example. 
     If at step S 521  it is not a WEB request coming from an Internet navigator but a request coming from a dedicated “peer-to-peer” application the server sends back an error to the requester. 
     For example the HTML page may have the following content: 
     
       
         
               
             
           
               
                   
               
             
             
               
                 &lt;HTML&gt; 
               
               
                 &lt;HEAD&gt; 
               
               
                 &lt;SCRIPT LANGUAGE=“VBscript”&gt; 
               
               
                 &lt;!-- 
               
               
                 detectableWithVB = False 
               
               
                 If ScriptEngineMajorVersion &gt;= 2 then 
               
               
                      detectableWithVB = True 
               
               
                 End If 
               
               
                 Function detectActiveXControl(activeXControlName) 
               
               
                      on error resume next 
               
               
                      detectActiveXControl = False 
               
               
                      If detectableWithVB Then 
               
               
                       detectActiveXControl = 
               
               
                 IsObject(CreateObject(activeXControlName)) 
               
               
                      End If 
               
               
                 End Function 
               
               
                 rem --&gt; 
               
               
                 &lt;/SCRIPT&gt; 
               
               
                 &lt;SCRIPT LANGUAGE=“JavaScript”&gt; 
               
               
                 &lt;!-- 
               
               
                 var pluginFound = false; 
               
               
                 pluginFound = detectActiveXControl(‘MpActiveXVB.MpRegistry’); 
               
               
                 alert(‘MpActiveXVB found = ’ + pluginFound); 
               
               
                 if (pluginFound) 
               
               
                 { 
               
               
                     // Insert reference to activeX in HTML page 
               
               
                     document.write(“&lt;OBJECT ID=”); 
               
               
                     document.write(‘\“MpActiveXVB\”’); 
               
               
                     document.write(“CLASSID=”); 
               
               
                     document.write(‘\“CLSID:443E61FC-4AC1-49EC-A89A- 
               
               
                 F99EA5EE72A2\”&gt;’); 
               
               
                     document.writeIn(“&lt;/OBJECT&gt;”); 
               
               
                 } 
               
               
                 // --&gt; 
               
               
                 &lt;/SCRIPT&gt; 
               
               
                 &lt;/HEAD&gt; 
               
               
                 &lt;BODY&gt; 
               
               
                 &lt;SCRIPT LANGUAGE=“JavaScript”&gt; 
               
               
                 &lt;!-- 
               
               
                 var isLocalServerActif = false; 
               
               
                 var localServerHTTPPort = 80; 
               
               
                 function CheckServer( ) 
               
               
                 { 
               
               
                  if (pluginFound) 
               
               
                  { 
               
               
                   isLocalServerActif = 
               
               
                 MpActiveXVB.GetRegValue(“SOFTWARE\\Classes\\CLSID\\ 
               
               
                 {443E61FC-4AC1-49EC-A89A-F99EA5EE72A2}”); 
               
               
                   if(isLocalServerActif == false) 
               
               
                   { 
               
               
                    alert(‘Server Not Found’); 
               
               
                   } 
               
               
                   else 
               
               
                   { 
               
               
                    localServerHTTPPort = 
               
               
                 MpActiveXVB.GetRegValue(“SOFTWARE\\localserver\\config\\port”); 
               
               
                    alert(‘Server Port Value: ’ + localServerHTTPPort); 
               
               
                   } 
               
               
                  } 
               
               
                 } 
               
               
                 function GetRessourceAddress (imageID, title) 
               
               
                 { 
               
               
                  document.writeIn(“”); 
               
               
                  document.writeIn(“Process the image ID...”); 
               
               
                  if(isLocalServerActif == false) 
               
               
                  { 
               
               
                   document.write(“&lt;A HREF=http://www.server.com/”); 
               
               
                  } 
               
               
                  else 
               
               
                  { 
               
               
                   document.write(“&lt;A HREF=http://localhost:”); 
               
               
                   document.write(localServerHTTPPort); 
               
               
                   document.write(“/”); 
               
               
                  } 
               
               
                  document.write(imageID); 
               
               
                  document.write(“&gt;&lt;IMG SRC=”) ; 
               
               
                  document.write(title); 
               
               
                  document.write(“BORDER=0 ALT=”); 
               
               
                  document.write(title); 
               
               
                  document.writeIn(“&gt;&lt;/A&gt;”); 
               
               
                 } 
               
               
                 CheckServer ( ); 
               
               
                 // --&gt; 
               
               
                 &lt;/SCRIPT&gt; 
               
               
                 &lt;NOSCRIPT&gt; 
               
               
                 &lt;H1&gt;No JavaScript&lt;/H1&gt; 
               
               
                 You see this text if JavaScript is disabled or unimplemented. 
               
               
                 &lt;/NOSCRIPT&gt; 
               
               
                 &lt;SCRIPT LANGUAGE=“JavaScript”&gt; 
               
               
                 GetRessourceAddress (‘abcde23404-3143492ef-23232’, ‘blue —   
               
               
                 mountain.jpg’); 
               
               
                 GetRessourceAddress (‘fffffeeeaa-bbe478999-aaaaa’, ‘red —   
               
               
                 mountain.jpg’); 
               
               
                 &lt;/SCRIPT&gt; 
               
               
                 &lt;/BODY&gt; 
               
               
                 &lt;/HTML&gt; 
               
               
                   
               
             
          
         
       
     
     Among the numerous advantages conferred by the present invention, it is possible to highlight that it is not necessary to adapt the content of the notification according to the capabilities of the recipients, that is to say according to whether they possess the dedicated P2P local application or not. Furthermore, the local or remote access is totally transparent for the user. Similarly, it is not necessary to modify the Internet configuration of the user (in this case the addresses of the proxy server or proxy. Finally, the client devices possessing the P2P application are not obliged to keep their local server active to be able to display the content of a notification received by email, the display of the notification adapting itself automatically depending on the presence/absence of a local server.