Abstract:
The invention provides a method and system for sending relatively identical web pages, when requested by subsequent users, with substantial reduction of bandwidth. The server determines a “template web page” corresponding to the actual information on the web page, and having a set of insertion points, at which changed data can be inserted by the client. The server sends a JavaScript program corresponding to the template web page, which makes reference to the template web page and the changed data, along with sending the actual changed data itself. A first user requesting the web page receives the entire web page, while a second user requesting the web page (or the first user re-requesting the web page at a later time) receives the template information plus only the changed data. The server re-determines the template web page from time to time, such as when a ratio of changed data to template web page data exceeds a selected threshold. The server identifies the particular template web page to the client using a unique identifier (an “E-tag”) for the particular data sent in response to the request. Since the E-tag refers to the template, not the underlying web page, when the standard client makes its conditional request for the web page “if not changed”, the server responds that the web page is “not changed” even if it really is, but embeds the changed data in a cookie it sends to the client with the server response to the client request.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to differential caching. 
   2. Related Art 
   When users (at client devices) request information from a server (at a server device), it often occurs that those users request identical, or nearly identical, information from the server. When the requested information is identical, there are known techniques for providing identical information without incurring the same amount of resource burden on the server. For one example, a single proxy for multiple users can cache the identical information, and simply provide the identical information to each user (after the first) who requests that information. This method is known in the art as “proxy caching”. For a second example, the server can maintain its own cache, and similarly provide the identical information to each user (after the first) who requests that information. This method is known in the art as “reverse proxy caching”. 
   While these known methods generally achieve the goal of providing identical information to multiple users, they are unable to provide information that is not identical, even if that non-identical information is very similar. For example, information can be non-identical, even if very similar, for one or more of the following reasons:
         The web page requested by users includes a banner ad that is changed at relatively frequent intervals by the server or by a redirected server for the banner ad.   The web page requested by users includes a report of data from a database that is changed at relatively frequent intervals. One example of such a database includes a database of stock market prices or related data.   The web page requested by users includes personalization or other data specific to the user requesting the page. One example of such a web page includes a web page with local news or weather reports specific to the locale of the requesting user.       

   Known methods of sending such non-identical information include “delta encoding”, in which the server determines a set of changes between an earlier web page served to an earlier request, and a new web page served in response to a new request. While these methods of delta encoding can obtain significant compression of a new web page, it suffers from several drawbacks. First, these methods depend on the server being able to determine a version of the web page that the requesting user already has, so as to be able to send only changes from that base web page. Thus, if the requesting user does not have an earlier copy of the web page (or if the earlier copy of the web page is relatively stale), the degree of effective compression is substantially reduced. Second, these methods depend on the server and the user having a protocol by which the server can send only changes to the base web page. Thus, if the requesting user does not implement that protocol, there is no substantial advantage obtained. 
   Accordingly, it would be desirable to provide a technique for providing relatively identical (but still non-identical) web pages, when requested by subsequent users, with substantial reduction of bandwidth or other resource consumption, that is not subject to drawbacks of the known art. 
   SUMMARY OF THE INVENTION 
   The invention provides a method and system for sending relatively identical (but still non-identical) documents, when requested by subsequent users, with substantial reduction of bandwidth or other resource consumption by the server. In a preferred embodiment, the server determines at least one “template document” corresponding to the actual information on the document, and having a set of insertion points, at which changed (or personalized) data can be inserted by the client. In a preferred embodiment, the document includes a web page, but other types of document (such as for example bulletin boards or newsgroups, email or groupware messages, database entries, or other frequently requested information) would be within the scope and spirit of the invention. 
   The server sends a web page including a code fragment capable of being executed at the client without further knowledge by the client of the techniques used by the invention. In a preferred embodiment, the code fragment includes a JavaScript program, but other executable or interpretable instructions (such as for example email macros or scripts, XML extensions, or other program scripts) would be within the scope and spirit of the invention. 
   The program code fragment corresponds to a selected template web page; the code fragment makes reference to a template web page including a set of insertion points for changed data, along with sending the actual changed data itself. A first user requesting the web page receives the entire web page, while a later user requesting the web page (or the first user re-requesting the web page at a later time) receives the template information plus only the changed data. This later user might be (a) the very next user, (b) a later user after the web page has been sent several times, or (c) the first user might be sent the original page as a “template”, with the hope that later “changed” information will be zero length. Thus, the later client with access to the template web page can receive only the changed data, substantially reducing the amount of bandwidth or other resources used for the transfer. 
   In a preferred embodiment, the server re-determines the template web page from time to time, such as when a ratio of changed data to template web page data exceeds a selected threshold. Thus, the server can have multiple template web pages corresponding to a set of actual web page data. The server identifies the particular template web page to the client using a unique identifier (herein called an “E-tag”) for the particular data sent in response to the request (thus, the entire actual web page would have a different E-tag from the template web page). 
   When the client requests the web page, it makes a conditional request, indicating the E-tag for those versions of the template web page it has. (This does not require modification of the client, because most clients already make conditional requests for web pages, indicating those web pages they already have in their local cache.) The server examines the E-tag in the conditional request, and in response thereto, determines if the client has at least one non-stale version of at least one template web page, and if so, which one of those template web pages is preferred for minimizing time for sending the changed data for the newest version of the web page. Thus, if the client already has a non-stale template, the server can just send the changed data. Alternatively, the server can send a new template, plus the changed data for insertion, plus a new E-tag for the new template. Since the E-tag refers to the template, not the underlying web page, when the standard client makes its conditional request for the web page “if not changed”, the server responds that the web page is “not changed” even if it really is, but embeds the changed data in a cookie it sends to the client with the server response to the client request. 
   The invention has general applicability to compression and sending of information, not limited specifically to web pages, use of web protocols, or caching. For example, embodiments of the invention can include one or more of, or some combination of, the following applications:
         Compression or sending of real-time data, where that data varies substantially only for a small part of the data.   Compression or sending of messages, including email or groupware messages, bulletin board or newsgroup messages.   Compression or sending of database responses, including responses to common or frequently-used database queries.       

   Moreover, techniques used by a preferred embodiment of the invention for compression or sending of information can be used in contexts other than the specific applications disclosed herein. For example, techniques used by embodiments of the invention for compression and sending of information are all generally applicable to fields other than the specific applications disclosed herein. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a block diagram of a system for performing methods shown herein. 
       FIG. 2  shows a data flow diagram for methods shown herein. 
       FIG. 3  shows a process flow diagram of a method for compression and sending information. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The invention is described herein with regard to preferred steps and data structures. Those skilled in the art will recognize, after perusal of this application, that the described steps and data structures are not limited to any particular processing devices (whether general-purpose or special-purpose processing devices, or specific circuitry). Rather, those of ordinary skill in the art would be able to implement the described steps and data structures, and equivalents thereof, without undue experimentation or further invention. All such implementations are within the scope and spirit of the invention. 
   Lexicography 
   The following terms refer or relate to aspects of the invention as described below. The descriptions of general meanings of these terms are not intended to be limiting, only illustrative.
         client and server—As used herein, the phrases, “client” and “server” refer to a relationship between two devices, particularly to their relationship as client and server, not necessarily to any particular physical devices.   client device and server device—As used herein, the phrase “client device” includes any device taking on the role of a client in a client-server relationship (such as an HTTP web client and web server). There is no particular requirement that any client devices must be individual physical devices; they can each be a single device, a set of cooperating devices, a portion of a device, or some combination thereof. As used herein, the phrase “server device” includes any device taking on the role of a server in a client-server relationship. There is no particular requirement that server devices must be individual physical devices; they can each be a single device, a set of cooperating devices, a portion of a device, or some combination thereof.   Document—As used herein, the term “document” includes any collection of information sent to the recipient operator or user, and thus includes at least any of the following (a) multiple versions of the same web page, file, or other network object; or (b) data that is generated dynamically for presentation as a web page, file, or other network object, such as by a script that generates different versions of a document dynamically from a number of sources, such as by querying a database, generating a session ID, and the like.   logically remote—As used herein, the phrase “logically remote” refers to the relative logical placement or degree of connectivity between two or more computerized systems or two or more elements within a single system. Generally, elements that are relatively proximate to each other may be logically remote if there is a small probability that information will flow between them on a regular basis.   operator—As used herein, the term “operator” refers to any actor capable of performing the functions of an operator ad described herein. An “operator” might comprise an individual person, a set of persons having authority to act in particular way, a proxy for an individual person or set of persons, such as a human secretary or a computer program having the function of forwarding or aggregating or scheduling requests made by others, or even an AI (artificial intelligence) program such as an expert system or otherwise. There is no particular requirement that the operator must have a particular level of authority or intelligence, so long as the operator has the capability of issuing instructions attributed to the operator as described herein.   workstation—As used herein, the term “workstation” refers to any device capable of performing the functions of a workstation as described herein. A workstation might comprise an individual computing device, a set of multiple computing devices operating in concert or cooperation, a portion of a computing device used for a particular function (such as a software package used on an otherwise general-purpose device), or some combination or mixture thereof. There is no particular requirement that a “workstation” include any particular computing device: a “workstation” might include a personal computer, a software package on a server, a handheld computer cooperating with a personal computer or with a server (or both), or a telephone interface to a system such as an interactive voice response system. There is also no particular requirement that multiple workstations used by a single collaborator need be of the same type. For example, a single collaborator might have a single server for access to the hub, a set of personal computers each having separate access to the hub (or alternatively, separate access to a subset of functions of the hub), and a set of handheld computers used by personnel in the field for access to the hub.       

   As noted above, these descriptions of general meanings of these terms are not intended to be limiting, only illustrative. Other and further applications of the invention, including extensions of these terms and concepts, would be clear to those of ordinary skill in the art after perusing this application. These other and further applications are part of the scope and spirit of the invention, and would be clear to those of ordinary skill in the art, without further invention or undue experimentation. 
   System Elements 
     FIG. 1  shows a block diagram of a system for performing methods shown herein. 
   A system  100  includes one or more clients  110 , a server  120 , and a communication network  130 . 
   Client Devices 
   Each client  110  includes a client workstation  111  and a client operator  112 . 
   Also as noted above, there is no particular requirement that a “workstation” include any particular computing device: a “workstation” might include a personal computer, a software package on a server, a handheld computer cooperating with a personal computer or with a server (or both), or a telephone interface to a system such as an interactive voice response system. There is also no particular requirement that multiple workstations used by a single client need be of the same type. For example, a single client might have a single server for access to the hub, a set of personal computers each having separate access to the hub (or alternatively, separate access to a subset of functions of the hub), and a set of handheld computers used by personnel in the field for access to the hub. 
   As noted above, in general when an element is described as an “operator” it might comprise an individual person, a set of persons having authority to act in particular way, a proxy for an individual person or set of persons, such as a human secretary or a computer program having the function of forwarding or aggregating or scheduling requests made by others, or even an AI (artificial intelligence) program such as an expert system or otherwise. There is no particular requirements that the operator must have a particular level of authority or intelligence, so long as the operator has the capability of issuing instructions attributed to the operator as described herein. 
   Each client  110  includes a web browser  113 , such as the “Internet Explorer” product or the “Netscape Navigator” product. The web browser  113  is capable of using a message transfer protocol, such as HTTP (hypertext transfer protocol), or a variant thereof, to request documents (such as for example web pages) from the server  120  and to receive documents and other responses from the server  120 . In a preferred embodiment, the web browser  113  uses HTTP version 1.1, or at least some features thereof, as described herein. 
   Server Device 
   The server  120  includes a computer  121  and a database  122  of documents  123 . In a preferred embodiment, documents  123  can include (as further described herein) web pages, embedded objects for web pages, template web pages, changed data for insertion into template web pages, and code fragments. 
   The server  120  includes a processor, program and data memory, and operates under control of software to perform the tasks described herein. In particular, the server  120  is capable of using a message transfer protocol, such as HTTP or a variant thereof, to receive requests for documents (such as for example web pages) from clients  110  and to respond to those requests by sending those documents to clients  110 . In a preferred embodiment, the server  120  uses HTTP version 1.1, or at least some features thereof, as described herein. 
   Communication Network 
   The individual clients  110  and the server  120  are coupled using a communication network  130 . The communication system  140  is capable of transferring messages from a sender to a set of receivers, such as from a collaborator  110  to the hub  130 , from a supplier  120  the hub  130 , or from the hub  130  to either a set of collaborators  110  or from the hub  130  to a set of suppliers  120 . 
   In a preferred embodiment, the communication system  140  includes a computer communication network, such as the Internet. However, in alternative embodiments, the communication system  140  might include an intranet, extranet, VPN (virtual private network), ATM system, a portion of a private or public PSTN (public switched telephone network), a frame relay system, or any other communication technique capable of performing the functions described herein. 
   Reverse Proxy Cache 
   In a preferred embodiment, the server  120  is coupled to a reverse proxy cache  130 , as described below. The reverse proxy cache  130  includes a processor, program and data memory, and mass storage, and is capable of performing the tasks described herein. In particular, the reverse proxy cache  130  records documents in its mass storage in response to action by the server  120  in sending those documents to clients  110 . When the reverse proxy cache  130  receives requests for documents from a particular client  110 , it can respond to those requests by sending the document to that client  110 , or can forward the request to the server  120 . When the reverse proxy cache  130  notes a document sent by the server  120  to a client  110 , it can record that document in its mass storage, so as to later recognize requests for that document from clients  110  (either the same client  110  asking for the same document a second time, or a second client  110  asking for that document). 
   As described herein, although in a preferred embodiment the server  120  uses a reverse proxy cache  130 , and although in alternative embodiments the system  100  uses a proxy cache  140  or an ASP caching server  150 , there is no particular requirement for use of a cache. Rather, the server  120  can send the documents described herein directly to clients  110 , without loss of any functionality. 
   As described herein, the invention has additional value when used in combination with one or more caches (whether a reverse proxy cache  130 , a proxy cache  140 , an ASP caching server  150 , or another type of caching device). As described below, one or more caches in a communication path between a particular client  110  and the server  120  might have a template web page providing a good match with information that client  110  already has, and thus would be able to send to the client  110  only changed data for that template web page. If any of the caches in the communication path have a template web page providing a good match, a preferred embodiment is able to provide the advantages of compression, transparently without the client  110 , the server  120 , or any other intermediate cache having to act differently or even know about the form of compression described herein, so long as the parts of the compressed document (the code fragment and the cookie with changed data, as described below) can be forwarded from the originating cache to the client  110  without any changed action on the part of any intermediate cache. 
   Alternative Proxy Caches 
   In a first set of alternative embodiments, the client  110  may use a (client side) proxy cache  140 , which performs the task of caching at the “client side” of communication between the client  110  and the server  120 . 
   The proxy cache  140  may be located either (a) in the same device as the client  110 , such as a software proxy cache; (b) in a device logically near to the client  110 , such as coupled to a LAN (local area network) with the client  110 ; or (c) in a device more logically remote from the client  110 , such as coupled to a number of clients  110  and serving to provide proxy caching services to those clients  110 . Examples of a proxy cache  140  of type C include those proxy caches  140  used by ISPs (internet service providers) and the like. 
   In these first alternative embodiments, the proxy cache  140  performs the tasks otherwise attributed to the reverse proxy cache  130 . 
   In a second set of alternative embodiments, the system  100  may include an ASP caching server  150 , which performs the tasks otherwise attributed to the reverse proxy cache  130  or to the proxy cache  140 . 
   In a third set of alternative embodiments, the system  100  may include more than one such proxy cache, including such combinations of reverse proxy caches  130 , proxy caches  140  (of various types), and ASP caching servers  150 . There is no particular requirement in any embodiment that the server  120  or any type of cache is required to perform its tasks in a particular location. 
   Data Flow Diagram 
     FIG. 2  shows a data flow diagram of methods shown herein. 
   A data flow diagram  200  includes representations of a set of documents and related data, and processes for operation on those data. 
   The server  120  includes an original data document  210  (such as a web page), including a set of unchanged content  211  and a set of changed data  212 . 
   In a data flow process  220  identified as “templatization”, the server  120  examines the original data document  210  from time to time and constructs a template document  230  (such as a template web page), including a set of unchanged content  231  and a set of insertion points  232 . Each insertion point  232  represents a pointer to changed data  212 , recorded in a cookie  233  or other data structure. In a preferred embodiment, the server  120  constructs the template document  230  in response to the original data document  210  at least at the following times:
         when the original data document  210  is first made available for requests at the server  120 ;   after a selected period of time (such as for example, every hour);
 
or
   when the size of the changed data  212  is larger than a selected fraction of the size of the original data document  210  (such as for example, when the changed data  212  exceeds 10% of the original data document  210 .       

   In a data flow process  240  identified as “unification”, it might occur that there are different versions of the template document  220  at the client  110  and at the server  120 . The server  120  compares the template document  220  at the client  110  (identified by its E-tag, as described herein) with the template document  220  at the server  120 , so as to determine that the template documents  220  are the same, or at the least sufficiently similar so that changed data  212  can be inserted into the template document  220  at the client  110  using the cookie  233 . 
   In a data flow process  250  identified as “data insertion”, the client  110  inserts the changed data  212  from the cookie  233  into the template document  220 , to provide a copy of the original data document  210  in the form it was in at the server  120 . 
   Method of Operation 
     FIG. 3  shows a process flow diagram of a method for compression and sending information. 
   A method  300  includes a set of flow points and process steps as described herein. 
   Although by the nature of textual description, the flow points and process steps are described sequentially, there is no particular requirement that the flow points or process steps must be sequential. Rather, in various embodiments of the invention, the described flow points and process steps can be performed in a parallel or pipelined manner, either by one device performing multitasking or multithreading, or by a plurality of devices operating in a cooperative manner. Parallel and pipelined operations are known in the art of computer science. 
   At a flow point  310 , a client  110  is ready to make a request for a document (such as the original data document  210 ) from the server  120 . In a preferred embodiment, each individual document request is performed independently, even if a plurality of document requests are to be performed substantially simultaneously. 
   At a step  311 , the client  110  generates a request message  161  (shown in  FIG. 1 ) for the document. The request message  161  identifies the document and requests that the server  120  send the document to the client  110 . 
   In a preferred embodiment, the request message  161  includes an HTTP “last-modified/if-modified-since” protocol message or an HTTP “E-tag/if-none-match” protocol message. For example, if the client  110  has template versions #1, #2 and #3 for the web page “Fireclick.html” at its local cache, and the client operator  112  requests that web page, the client  110  generates the following HTTP request: 
   GET /A.html HTTP/1.1 
   Host: www.site.com 
   If-None-Match: 1,2,3 
   At a step  312 , the server  120  determines if it has a template document  230  for the requested original data document  210 . 
   If the server  120  does not have a template document  230 , the server  120  simply generates a response message  162  to the client  110 , and the method  300  continues with the flow point  320  (successful delivery of the original data document  210  to the client). As part of this step, in a preferred embodiment, the server  120  will then attempt to templatize the original data document  210 , to provide a template document  230  for the requested original data document  210  (for future requests). 
   If the server  120  does have a template document  230 , the method  300  proceeds with the next step. 
   At a step  313 , the server  120  identifies its best (such as for example most recent) template document  230  for the requested document. If the best template document  230  is one of the template documents  230  at the client  110 , the method  300  performs this step, and continues with the flow point  320 . If the best template document  230  is not one of the template documents  230  at the client  110 , the method  300  performs the next step  314 , and continues with the flow point  320 . 
   At part of this step, the server  120  generates a response message  162  sending the identified template document  230  to the client  110 , along with a cookie  233  including changed data to be inserted at insertion points  232  in the template document  230 . As described herein, at the insertion points  232 , the template document includes code fragments (such as for example JavaScript) capable of reading the changed data  212  in the cookie  233  and inserting that changed data  212  into the template document  230  at the client  110 . 
   In a preferred embodiment, the response message  162  includes an HTTP “ 304  content not-modified” protocol message, with an included HTTP “set-cookie” option. The associated cookie includes only the changed data  212 . As described below, the client  110  will receive the response message  162 , re-parse the HTML page, re-execute the JavaScript, which reads in the new cookie, and therefore renders the new original data document  210  from the same template document  230 . 
   Using the example above, presume the client  110  had template versions #1, #2 and #3 for the web page “Fireclick.html” at its local cache, and the client operator  112  requested that web page. When the server  120  receives that request, the server  120  generates (or retrieves) the original data document  210  for “Fireclick.html”. The server  120  compares the original data document  210  with the versions of the template document  230  present at the client  110  and picks one, such as for example #2. The server  120  determines the changed data  212  and encodes them into the cookie  233 . If for example, the changed data is the text string ‘patentapplication’, the server  120  will make the following HTTP response: 
     304  HTTP/1.1 Not-Modified 
   ETag: 2 
   Set-Cookie: delta=patentapplication 
   At a step  314  (the best template document  230  was not one of the template documents  230  at the client  110 ), the server  120  compares the original data document  210  with the new template document  230 , and generates a response message  162  including the new template document  230  and the changed data  212  in the cookie  233 . Using the example above, if the new template document  230  at the server  120  is #4, and the changed data is the text string ‘patent’, the server  120  will make the following HTTP response: 
     200  HTTP/1.1 OK 
   ETag: 4 
   Set-Cookie: delta=abcd 
   &lt;HTML contents of the template, including JavaScript&gt; 
   At a flow point  320 , the client  110  has received the response message  162 , and has one of the following:
         the original data document  210 ;   an E-tag for a template document  230  already at the client  110 , plus changed data  212  in a cookie  233 ;
 
or
   a new template document  230 , plus changed data  212  in a cookie  233 .       

   At a step  321 , the client  110  parses the received document, performs any code fragments (JavaScript at insertion points  232 ), and inserts any changed data  212 , so as to render a copy of the original data document  210  at the server  120 . 
   At a flow point  330 , the method  300  has completed delivery of a copy of the original data document  210  from the server  120  to the client, and is ready to process a new request. 
   Generality of the Invention 
   The invention has general applicability to compression and sending of information, not limited specifically to web pages, use of web protocols, or caching. For example, embodiments of the invention can include one or more of, or some combination of, the following applications:
         Compression or sending of real-time data, where that data varies substantially only for a small part of the data.   Compression or sending of messages, including email or groupware messages, bulletin board or newsgroup messages.   Compression or sending of database responses, including responses to common or frequently-used database queries.       

   Moreover, techniques used by a preferred embodiment of the invention for compression or sending of information can be used in contexts other than the specific applications disclosed herein. For example, techniques used by embodiments of the invention for compression and sending of information are all generally applicable to fields other than the specific applications disclosed herein. 
   Other and further applications of the invention in its most general form would be clear to those skilled in the art after perusal of this application. The invention would be usable for such other and further applications without undue experimentation or further invention. 
   Although preferred embodiments are disclosed herein, many variations are possible which remain within the concept, scope and spirit of the invention; these variations would be clear to those skilled in the art after perusal of this application.