Patent Publication Number: US-7593943-B2

Title: Method and system for synchronizing multiple user revisions to a shared object

Description:
BACKGROUND OF THE INVENTION 
   File sharing applications allow several different users to collectively share information. Many users may access the same file simultaneously. All of the users may view the file but only the first user to access the file has editing privileges. Subsequent users to access the file are blocked from editing the file. Supplying a read-only version of a file to all but one user is inconvenient for large shared files. This is particularly exacerbated if users want to work on a shared file offline. For example, other users may be locked out of the file for a long period of time if the first user to access the shared file is away on a business trip. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a method and system for synchronizing multiple user revisions to a shared object. The object may be any entity capable of being shared such as a file. Many different users may access, revise and update the same shared object simultaneously through several different transports. The users are not blocked from accessing and revising a shared object when another user has access to the shared object. Any authorized users may simultaneously revise the shared object. Users are not required to be connected to the shared object while making revisions. The revisions may be made offline to a local cached version of the object. The revisions are then synchronized with other user revisions when the shared object is available. Revisions to the shared object are automatically synchronized such that all users can view the revisions to the shared object. Different users may revise the shared object at different times such that multiple versions of the shared object may coexist. The latest version of the shared object is the version that includes the most recent synchronized revisions that are available to other authorized users. 
   A conflict may occur when two users revise the same portion of the shared object. The revised portion cannot be synchronized with the shared object if it conflicts with another user&#39;s revision to the same portion. The portion of the shared object having the conflicting revision is displayed on a conflict page. The conflict page resembles a corresponding master page of the latest version of the shared file except that the portion of the shared object having the conflicting revision is highlighted and displayed in place of the synchronized revision. A conflict indicator is displayed on the master page of the shared object. The conflict page is displayed alongside the master page when the conflict indicator is selected. The user is presented with both the synchronized state of the master page and the corresponding conflict page. The user may reconcile and merge the conflicting revisions into the master page. Conflicting revisions that are identified as irrelevant may be purged. 
   In one aspect of the invention, a revision to a shared object is received. A determination is made whether the revision conflicts with a synchronized revision on a master page of the shared object. The revision is synchronized with the shared object when the revision is determined to be associated with a current version of the shared object and when the revision is determined to be not conflicting with a synchronized revision. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a computing device that may be used according to an example embodiment of the present invention. 
       FIG. 2  illustrates a block diagram of a system for synchronizing multiple user revisions to a shared object, in accordance with the present invention. 
       FIG. 3  illustrates a hierarchical graph of linked nodes that indicate different portions of a shared object, in accordance with the present invention. 
       FIG. 4  illustrates a master page of a shared object and an associated conflict page, in accordance with the present invention. 
       FIG. 5  illustrates a block diagram of a system for synchronizing multiple user revisions to a shared object, in accordance with the present invention. 
       FIG. 6  illustrates an operational flow diagram illustrating a process synchronizing multiple user revisions to a shared object, in accordance with the present invention. 
       FIG. 7  illustrates an operational flow diagram illustrating a process for reconciling and merging conflicting revisions from multiple users in a shared object, in accordance with the present invention. 
       FIG. 8  illustrates an operational flow diagram illustrating a process for synchronizing multiple user revisions to a shared object, in accordance with the present invention. 
       FIG. 9  illustrates an operational flow diagram illustrating a process for seamlessly transitioning from asynchronous to synchronous communication modes, in accordance with the present invention. 
       FIG. 10  illustrates an operational flow diagram illustrating a process for seamlessly transitioning from synchronous to asynchronous communication modes, in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention is directed to a method and system for synchronizing multiple user revisions to a shared object. The object may be entity capable of being shared such as a file. Many different users may access, revise and update the same shared object simultaneously through several different transports. The users are not blocked from accessing and revising a shared object when another user has access to the shared object. Any authorized users may simultaneously revise the shared object. Users are not required to be connected to the shared object while making revisions. The revisions may be made offline to a local cached version of the object. The revisions are then synchronized with other user revisions when the shared object is available. Revisions to the shared file are automatically synchronized such that all users can view the revisions to the shared object. Different users may revise the shared object at different times such that multiple versions of the shared object may coexist. The latest version of the shared object is the version that includes the most recent synchronized revisions that are available to other authorized users. 
   A conflict may occur when two users revise the same portion of the shared object. The revised portion cannot be synchronized with the shared object if it conflicts with another user&#39;s revision to the same portion. The portion of the shared object having the conflicting revision is displayed on a conflict page. The conflict page resembles a corresponding master page of the latest version of the shared object except that the portion of the object having the conflicting revision is highlighted and displayed in place of the synchronized revision. A conflict indicator is displayed on the master page of the shared file. The conflict page is displayed alongside the master page when the conflict indicator is selected. The user is presented with both the synchronized state of the master page and the corresponding conflict page. The user may reconcile and merge the conflicting revisions into the master page. Conflicting revisions that are identified as irrelevant may be purged. 
   Illustrative Operating Environment 
   With reference to  FIG. 1 , one example system for implementing the invention includes a computing device, such as computing device  100 . Computing device  100  may be configured as a client, a server, a mobile device, or any other computing device that interacts with data in a network based collaboration system. In a very basic configuration, computing device  100  typically includes at least one processing unit  102  and system memory  104 . Depending on the exact configuration and type of computing device, system memory  104  may be volatile (such as RAM), non-volatile (such as ROM, flash memory, etc.) or some combination of the two. System memory  104  typically includes an operating system  105 , one or more applications  106 , and may include program data  107 . A revision synchronization module  108 , which is described in detail below, is implemented within applications  106 . 
   Computing device  100  may have additional features or functionality. For example, computing device  100  may also include additional data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape. Such additional storage is illustrated in  FIG. 1  by removable storage  109  and non-removable storage  110 . Computer storage media may include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. System memory  104 , removable storage  109  and non-removable storage  110  are all examples of computer storage media. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by computing device  100 . Any such computer storage media may be part of device  100 . Computing device  100  may also have input device(s)  112  such as keyboard, mouse, pen, voice input device, touch input device, etc. Output device(s)  114  such as a display, speakers, printer, etc. may also be included. 
   Computing device  100  also contains communication connections  116  that allow the device to communicate with other computing devices  118 , such as over a network. Networks include local area networks and wide area networks, as well as other large scale networks including, but not limited to, intranets and extranets. Communication connection  116  is one example of communication media. Communication media may typically be embodied by computer readable instructions, data structures, program modules, or other data in a modulated data signal, such as a carrier wave or other transport mechanism, and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. The term computer readable media as used herein includes both storage media and communication media. 
   Synchronizing Multiple User Revisions to a Shared File 
     FIG. 2  illustrates a block diagram of a system for synchronizing multiple user revisions to a shared object. The object may be any entity capable of being shared such as a file. The system includes clients  200 ,  210 ,  220 ,  230 , an email server with file storage capability such as exchange server  240 , web server  250 , peer-to-peer network  260  and email attachment  270 . Clients  200 ,  210  are coupled to exchange server  240 . Clients  210 ,  220  are coupled to web server  250 . Clients  210 ,  220  are also coupled together through peer-to-peer network  260 . Email attachment  270  is arranged to be transferred to and from client  230  by web server  250 . Clients  200 ,  210  are both associated with the same user (User  1 ). For example, client  200  is accessed by User  1  at home, and client  210  is accessed by User  1  at work. Clients  220 ,  230  are associated with different users (User  2  and User  3 , respectively). Clients  200 ,  210 ,  220 ,  230  each include cache  202 ,  212 ,  222 ,  232  for locally storing a shared object. Peer-to-peer network  260  includes virtual server  262  for transferring a shared object between clients  210 ,  220 . Revision file  242  and shared objects  252 ,  264 ,  272  are stored in exchange server  240 , web server  250 , virtual server  262  and email attachment  270 , respectively. Revision file  242  and shared objects  252 ,  264 ,  272  may be associated with a peer group identifier. The peer group identifier identifies the users who are authorized to access and revise a particular shared object (i.e., the peer group). In one embodiment, the peer group identifier is a uniform resource locator (URL) to the peer group that may be resolved to any web client. Shared objects  252 ,  264  are associated with manifest files  254 ,  266 , respectively. 
   Many different users may access, edit and update the same shared object simultaneously through several different transports. For example, User  1  at client  210  and User  2  at client  220 . may access shared object  252  from web server  250 . The shared object is stored locally in corresponding cache  212 ,  222 . Both User  1  and User  2  may revise shared object  252 . The revisions are synchronized with shared object  252  on web server  250  such that User  1  can see the revisions made by User  2 , and User  2  can see the revisions made by User  1 . 
   In another example, User  3  may share access of shared object  272  with User  2  through email attachment  270 . User  2  may revise a locally stored shared object and send an email message to User  3  with the entire shared object or just the revisions to the shared object attached. The revisions made by User  2  are synchronized with shared object  252  on web server  250 . When the email is received at client  230 , the revisions made by User  2  are automatically synchronized with the local shared object stored in cache  232 . User  3  may then make further revisions to shared object  272  and reply to User  2  with the entire shared object or just the revisions to the shared object included as email attachment  270 . The revisions made by User  3  are synchronized with shared object  252  on web server  250 . The shared object at client  220  is also updated to include the revisions made by User  3 . 
   In another example, User  1  may access a shared object either at home on client  200  or at work on client  210  through exchange server  240 . Exchange servers are often utilized when access to an external server is not permitted or not available. Revision file  242  includes revisions to the shared object. Revision file  242  may be transferred between clients  200 ,  210  through a universal serial bus (USB) drive, an email application, or some other mechanism that allows revisions to be transferred back and forth. The revisions are applied to clients  200 ,  210  such that the local shared object stored in caches  202 ,  212  may be updated. 
   Exchange server  240  may have a restriction on the size of files it can handle (e.g.,  2  megabytes maximum). User  1  may upload revision file  242  that includes any revisions to the shared object from client  200  to exchange server  240 . Revision file  242  may be transferred from client  200  to client  210  in subsections when revision file  242  exceeds the size limitations of exchange server  240 . The file protocol permits a request/fill process for transferring the subsections. In one embodiment, exchange server  240  is associated with an email application. Revisions made by another user (User  2 ) may be transferred from client  220  to client  210  through web server  250  or peer-to-peer network  260  and then transferred to client  200  through an email account issued to User  1 . In another embodiment, client  200  periodically polls exchange server  240  for a current revision file. 
   In another example, peer-to-peer network  260  may be established between clients  210 ,  220  when the connection from clients  210 ,  220  to web server  250  is lost or when User  1  and User  2  prefer to communicate directly and synchronously in real time. User  1  and User  2  may prefer to communicate through peer-to-peer network  260  because object sharing over web server  250  may result in a lag between when revisions are made at client  210  and when the revisions are available at client  220 . The lag may be a result of heavy server traffic. Peer-to-peer network  260  allows revisions to the shared object to be directly transferred between clients  210 ,  220  instead of through web server  250 . In one embodiment, peer-to-peer network  260  is a transmission control protocol/internet protocol (TCP/IP) direct network. The TCP/IP direct network allows revisions to be stored and retrieved quickly. 
   Clients  210 ,  220  may each have a copy of shared object  252  locally stored in cache  212 ,  222  when web server  250  connectivity is interrupted. The peer group identifier associated with shared object  252  indicates that both User  1  and User  2  are accessing the shared object simultaneously. The users become aware of each other when they both access an established peer-to-peer network (e.g., both users are working on laptop computers on the same airplane). Peer-to-peer network  260  allows User  1  and User  2  to simultaneously access revisions to shared object  264  on virtual server  262  and implement further revisions. The revisions are instantly replicated on clients  210 ,  220  such that User  1  and User  2  may actively collaborate on shared object  264 . Peer-to-peer network  260  may be disabled when User  1  and User  2  are no longer in the same vicinity (e.g., each user returns to their respective offices) or when User  1  and User  2  no longer wish to communicate in real time. Shared object  252  may then be accessed from web server  250 . The transition between accessing shared object revisions on peer-to-peer network  260  and web server  250  is automatic and seamless. 
   Clients  210 ,  220  may receive current revisions from both web server  250  and peer-to-peer network  260 . Each revision made to the shared object is associated with a global unique identifier (GUID) and a time stamp. The time stamp identifies the time when the revision was made. Client  210  may modify shared object  252  on web server  250 . Client  220  determines whether the local version of the shared object in cache  222  is current by comparing a GUID and a time stamp associated with the cached object to the GUID and the time stamp associated with shared object  252  on web server  250 . If the current version is not stored locally, the latest revisions that have not been implemented in the cached object are loaded from web server  250  to client  220  and synchronized with the local file. Thus, the entire shared object need not be loaded to client  220  each time the local version of the shared object is updated. 
   In one embodiment, client  220  may determine from the GUID and the time stamp associated with the revision that the same modifications are available from peer-to-peer network  260 . However, no action results because client  220  has already implemented the modifications. In another embodiment, client  220  may determine from the GUID and the time stamp associated with the revision that the same modifications are not available from peer-to-peer network  260 . Thus, client  220  submits the revisions to peer-to-peer network  260  such that other users connected to peer-to-peer network  260  may synchronize with the current version of the shared object. 
   Client  220  may receive another revision from peer-to-peer network  260 . The shared object in cache  222  is updated. Client  220  determines whether the current state of the shared object is also available on web server  250  using the GUID and the time stamp associated with the revision. If shared object  252  on web server  250  is not synchronized with the current state of the shared document, client  220  submits the latest revision to web server  250  such that shared object  252  may be updated. 
   Asynchronous communication may occur when a client revises the shared object while connected to the system through a physical server. Server limitations may cause shared object synchronizations to be delayed from the time the revisions are implemented by a user. In one embodiment, the client may be revising a locally cached version of the shared object while not connected to the system. Any revisions made by the client may be synchronized with the shared object when the client reconnects to the system through a server. The client may seamlessly transition between local access, synchronous and asynchronous communication such that the user is not aware that the mode of communication has changed. A user may change location and any available data sharing transports (e.g., peer-to-peer networks, servers) are automatically identified. Thus, the user may access a shared object and collaborate with other authorized users through different mechanisms. 
   Each shared object is associated with a manifest file. The manifest file identifies the locations where other versions and instances of the shared object are stored within the system. In one embodiment, the manifest file is an extensible markup language (XML) file. In another embodiment, the manifest file identifies multiple shared objects. In another embodiment, the manifest file may be associated with any object that may be shared between clients. For example, the manifest file may be associated with an entire shared object or any portion of the shared object (e.g., a content container, a section, a page, an outline, etc.). 
   The manifest file may be stored anywhere within the system. As shown in the figure, manifest file  254  is associated with shared object  252 . Both shared object  252  and manifest file  254  are stored on web server  250 . In another embodiment, the manifest file is stored in the shared object. In yet another embodiment, the manifest file is stored in an active directory. In still yet another embodiment, the manifest file is stored in multiple locations within the system. The manifest file is stored in a location identified by a unique location identifier. The unique location identifier may identify a file server, a shared area of a server, a web server, or a peer group. 
   The shared object may be accessed locally from a cache, through a server, or through a peer-to-peer network. The client retrieves the manifest file from the location identified by the unique location identifier in the corresponding shared object. In one embodiment, the client may store the manifest file locally for future reference. The manifest file indicates the location of any other versions and instances of the shared object within the system (e.g., in a substore or a peer group). If another version/instance of the shared object is stored in a peer group, the manifest file may include the corresponding peer group identifier. 
   In one embodiment, client  220  accesses shared object  252  on web server  250 . Client  220  is automatically connected to other clients that are also accessing shared object  252  (e.g., the peer group). Client  220  retrieves manifest file  254  associated with shared object  252 . Manifest file  254  identifies the locations of different versions and instances of shared object  252 . Thus, client  220  may establish a peer-to-peer network with any other client in the peer group when any client in the peer group accesses a version/instance of shared object  252  identified by manifest file  254 . Client  220  may then disconnect from web server  250  and continue to access shared object  252  on the peer-to-peer network. 
   In another embodiment, client  210  may access shared object  264  from peer-to-peer network  260 . Client  210  retrieves manifest file  266  associated with shared object  264 . Client  210  may connect to a server and determine which clients are also connected to the server. The connected clients may be accessed through the server when peer-to-peer network  260  is not available. Shared object  264  (or  252 ) and associated manifest file  264  (or  254 ) allow client  210  (or client  220 ) to transition automatically and seamlessly between asynchronous and synchronous communication modes. 
   Users are not blocked from accessing and revising a shared object when another user has access to the shared object. Any authorized users may simultaneously revise the shared object. In one embodiment, a brief instance of blocking may occur to ensure the integrity of the revision transaction. For example, a user may extensively revise the shared document while disconnected from the server. When the user reconnects to the server, other clients may be briefly blocked from accessing the shared object until all of the user&#39;s revision are implemented in the shared object. 
     FIG. 3  illustrates a hierarchical graph of linked nodes that indicate different portions of a shared object. In one embodiment, the shared object is a notebook that is shared among several users. Notebook node  300  symbolizes the entire shared object. Folder node  310  is included within notebook node  300 . Section node  320  is included within folder node  310 . Page nodes  330 ,  335  are included within section node  310 . Table node  340 , ink node  342 , outline node  344 , and image node  346  are included within page node  330 . Outline element node  350  is included within outline node  344 . Text node  360  is included within outline element node  350 . Different nodes may be grouped together in a content container. For example, outline node  344 , outline element node  350 , and text node  360  may be grouped together as content container R 0 . Content container R 0  is assigned a GUID (e.g., GUID- 0 ). The GUID uniquely identifies content container R 0 . 
   A content container includes shared object content (e.g., a word, a sentence, a paragraph, a page, a table, a picture, handwriting, a uniform resource locator, or any combination of data included in the shared object). Content containers provide a dimension for object content that is grouped together. For example, a content container may correspond to a line, a paragraph, a page, or specific page elements (e.g., only the tables on a particular page). 
   The shared object stores an initial version of the graph. Specific operations may then be performed on individual content containers. For example, a user may revise the data of a content container. The revision to the shared object may be identified as a state of the content container. The shared object stores the revised content containers of the graph. A current state of the content container is compared to a previous state using GUIDs and time stamps such that a determination may be made whether the content container has been revised. 
   For example, two different users may each access the shared document and modify content container R 0 . One user may revise content container R 0  by deleting text node  360  (as shown in revision R 1 ). Revision R 1  is stored in the shared object. Revision R 1  is assigned a GUID (e.g., GUID- 1 ) to uniquely identify the revised container and a timestamp that identifies the time and date when revision R 1  is written to the shared object. Another user may revise content container R 0  by adding text node  380  to outline element node  350  (as shown in revision R 2 ). Revision R 2  is stored in the shared object. Revision R 2  is assigned a time stamp and a GUID (e.g., GUID- 2 ) to uniquely identify the revised content container. 
   Different users may revise a shared object at different times such that multiple versions of the shared object may coexist. However, there is only one latest version of the shared object. In one embodiment, the latest version of the shared object is the version that includes the most recent revisions that are synchronized with the shared object and made available to other authorized users. 
   For example, a user may revise a content container of a shared object that is identified as revision R 1  by adding outline element node  370  to outline node  344  (as shown in revision R 3 ). Revision R 3  is stored in the shared object. Revision R 3  is also assigned a time stamp and a GUID (e.g., GUID- 3 ) to uniquely identify the revised content container. Revision R 3  is an extension of revision R 1 . Thus, revision R 1  is the latest version of the shared object that the user was aware of (e.g., the locally stored version). The shared object is inspected to determine whether the latest version of the shared object is still revision R 1 . In one embodiment, the latest version of the shared object may be determined by comparing time stamps and GUIDs of different content containers. If the latest version of the shared object is associated with a more recent time stamp than revision R 1  then another user (e.g., the user who created revision R 2 ) has subsequently modified the same content container. 
   If another user has modified the same content container since revision R 1  was synchronized with the shared object, any revisions that are an extension of revision R 1  (e.g., revision R 3 ) may not be synchronized with the shared object until any subsequent revisions are synchronized with the shared object and any conflicting revisions are resolved and merged. For example, revision R 2  is synchronized with the shared object after revision R 1 . Thus, the latest version of the shared object includes revision R 2 . Before revision R 3  is synchronized with the shared object, revision R 3  is compared to revision R 2  to determine if any revisions conflict. The comparison is necessary because revision R 3  is an extension of revision R 1  which is no longer associated with the latest version of the shared object. Revision R 3  is determined to not conflict with revision R 2  because outline element node  370  can be added to outline node  344  without disrupting revision R 2 . 
   In one embodiment, the shared object is revised by moving a content container from one location to another within the shared object. For example, table node  340  may be moved from page node  330  to page node  335 . A determination is made that table node  340  has been moved but the new location cannot be determined. A proxy node is created at the original location of table node  340 . The proxy node is implemented at the new location of table node  340  when the new location of table node  340  is determined. If table node  340  is deleted before the new location is determined, the proxy node is discarded. 
   Different users may simultaneously edit the shared object. Usually, the users are revising different content containers of the shared object. Thus, each user&#39;s revisions may be synchronized with the shared object without further processing. A conflict may occur when two users edit the same content container of the shared object (e.g., the same table values, the same sentence). A conflict between different user revisions may result asynchronously. For example, a user may revise a locally cached version of the shared object when not connected to a server. The revisions are synchronized with the shared object when the user reconnects to the server. However, the revisions may conflict with other revisions that have already been synchronized with the shared object. 
   For example, revision R 4  is an extension of revision R 3 . Revision R 4  deletes outline element node  350  from outline node  344 . The latest version of the shared object is determined to include revision R 2 . A comparison between revision R 2  and revision R 4  identifies a conflict because outline element node  350  is present in revision R 2  but has been deleted in revision R 4 . 
   A three-way merge is performed between a master version of a content container and two divergent versions of the content container to resolve the conflicts. For example, content container R 0  (i.e., the master version), revision R 2 , and revision R 4  are merged to establish the current version of the shared object. The master version of a content container may be the version that was last synchronized with the shared object on the server. The master version includes non-conflicting revisions. 
   The conflicting content containers are reconciled and merged into the shared object by following a set of rules established by a merge algorithm. The merge algorithm determines which revisions are synchronized with the shared object. For example, different users may be ranked according to priority such that one user&#39;s revisions take precedence over all other users (i.e., primary edits). When a lower priority user attempts to revise a content container of the shared object that has already been revised by a higher priority user, the user is informed that the revisions (i.e., secondary edits) will not be synchronized the shared object. Thus, the primary edits are displayed on a master page of the shared object and any secondary edits are flagged as not being synchronized with the shared object. 
   In another example, revisions made to a shared object on a server have priority over revisions made locally on a client. The server copy of the shared object is deemed the master version because many different users have potentially accessed and revised the shared object on the server. Only one user has accessed and revised a locally stored version. Revised content containers that are not synchronized with the shared object (e.g., secondary edits) are identified as conflicting. The conflicting content containers are preserved by being stored on conflict pages associated with the corresponding master page of the shared object. 
     FIG. 4  illustrates a master page of a shared object and an associated conflict page. Master page  400  includes non-conflicting revisions such as content containers  410 ,  420 . Any unmerged conflicting revisions are identified on master page  400  by a conflict indicator. In one embodiment, the conflict indicator is drop down menu  430 . The first entry of drop down menu  430  may be the most recent conflicts generated by the user. The entry of drop down menu  430  may include the user&#39;s name and a corresponding time stamp. Another entry in drop down menu  430  may include other conflict pages that the user generated but did not reconcile. Other entries in drop down menu  430  may correspond to conflict pages generated by other users. Selecting an entry from drop down menu  430  displays the corresponding conflict page with the conflicting revisions highlighted to draw the user&#39;s attention to the revisions that were not merged in the master version of the shared object. Thus, the user may either reconcile and merge the conflicts with master page  400  or decide that the conflicts are irrelevant. 
   In another embodiment, the conflict indicator is a tab. The master page may be associated with tab  440 . Corresponding conflict pages may also be associated with tabs that are distinct from tab  440 . For example, the conflict page tabs may be indented with respect to tab  440  or collapsed below tab  440 . The conflict page that includes unmerged conflicts associated with a particular user may be identified by a tab that is distinct from the other tabs such that the user&#39;s attention is drawn to the conflict pages generated by that user. The user may then select the tab to navigate to the corresponding conflict page. 
   The selected conflict page may be displayed alongside the corresponding master page of the shared object such that the user may reconcile and merge any conflicting revisions in view of the merged revisions. Conflict page  450  is associated with master page  400 . Conflict page  450  resembles master page  400  except that any conflicting content containers are highlighted to indicate that the conflict has not been resolved. For example, content container  460  is presented with a highlighted background to draw the user&#39;s attention to the unmerged conflict. Content container  460  may have been deleted and synchronized with the shared object before a user revised data in content container  460  thereby creating a conflict. The user may select content container  460  to merge the revision on master page  400 . 
   In one embodiment, a conflict page is associated with one particular user. Thus, more than one conflict page may be associated with master page  400  when more then one user makes revisions on a page that cannot be merged. All conflicting revisions are stored for all users who are authorized to access the shared object. The user who accesses the conflict page presumably is most concerned with the conflicts generated by that user such that the user may reconcile those conflicts. For example, User  1  is presented with his corresponding conflict page when he selects the conflict indicator. The user may also view a conflict page associated with another user. For example, User  1  may select tab  470  to navigate to a conflict page associated with User  2 . 
   Many conflict pages associated with one master page of the shared object may accumulate over time. During that time period, the user may have synchronized several revisions with the master version of the shared object located on a server while ignoring any corresponding conflict pages. Thus, the older conflict pages that the user did not reconcile are presumably no longer relevant. In one embodiment, any conflict pages identified as irrelevant may be purged after a predetermined time period has elapsed and the user has synchronized revisions of the page during that time period. For example, the three most recent conflict pages associated with any master page are preserved while any other associated conflict pages are purged after a month from creation. 
   In one embodiment, conflict pages are not created during real time communication because conflicts may occur more frequently than during asynchronous communication. Instead, users may collaboratively revise the same content container. Any conflicts may be immediately disposed of since all users can quickly determine if their revisions have been implemented. Alternatively, a user is notified that another user is revising a particular content container. The user may be encouraged to revise a different content container until the other user&#39;s revisions are complete. 
     FIG. 5  illustrates a block diagram of a system for synchronizing multiple user revisions to a shared object. The system includes clients  500 ,  510 ,  540 ,  550  and servers  520 ,  530 . Client  500  is coupled to servers  520 ,  530 . Client  510  is coupled to server  520 . Clients  540 ,  550  are coupled to server  530 . Client  540  includes store  542  and child store  544 . Server  520  includes store  522  and child stores  524 ,  526 . Server  530  includes store  532 . Store  532  includes substores  534 ,  536 . 
   Stores  522 ,  532 , child stores  524 ,  526 , and substores  534 ,  536  may store revisions associated with a shared object. Store  522 ,  532 , child stores  524 ,  526  and substores  534 ,  536  are hierarchical. For example, store  522  may be associated with an entire shared notebook document. Child store  524  may be associated with a section of the shared notebook document. Child store  526  may be associated with a page of the shared notebook document. In one embodiment, only the most recent version of the top-level shared object is included in store  522 . Store  532  may store an entire top-level shared object. Substores  534 ,  536  are associated with portions of the shared object. For example, substore  534  may be associated with a section of the shared object, and substore  536  may be associated with a different section of the shared object. 
   An application may load a shared object from server  520  or server  530  to client  500  without a current version of a particular content container of the shared object. For example, client  500  requests a shared object from store  522 . The most recent available version of the shared object is presented at client  500 . The most recent available version of the shared object may not correspond to the current version of the shared object because data of the most recent revision is not available in the corresponding child store  526 . A request tag is assigned to child store  526  to indicate that client  500  requires the most recent revision data to update the shared object. Child store  526  may also be assigned a time stamp that identifies the time and date when client  500  requested the revision data from child store  526 . Child store may also be assigned a GUID that identifies the client that requested the data (e.g., client  500 ). The request tag, time stamp, and GUID are used to inform client  500  when another client accesses child store  526 . For example, client  510  may access child store  526  with the most current revision data. Thus, client  500  is informed that the most current revision data of the shared object is available in child store  526 . 
   Client  500  may be a user&#39;s home computer and client  540  may be a user&#39;s work computer. Server  530  may be an exchange server that transfers a revision file between clients  500 ,  540 . The revision file may be used to update a shared object stored on clients  500 ,  550 . In one embodiment, client  500  is restricted from handling files larger than a predetermined size (e.g., 2 megabytes). For example, client  500  may include an email application that limits the size of email messages that may be received. Store  542  includes revisions associated with a top-level shared object. Child store  544  includes revisions associated with a content container of the shared object. 
   Client  540  may poll server  530  to determine whether another client has submitted a data revision request. Client  540  may satisfy the request when the latest version of the requested data revision is available in store  542  or child store  544 . Client  540  may transfer the entire requested revision to client  500  if the size of the revision file is less than the limit that can be handled by client  500 . If the size of the revision file is greater than the limit, the file may be divided into smaller files that are less than the limit. Alternatively, the size of the revision file may be reduced by deleting previous requests. The smaller files are then transferred from client  540  to client  500  through server  530 . 
   Multiple requests for revision data may be waiting on a server. In one embodiment, the requests may be made from different clients (e.g., clients  500 ,  550 ). Each requesting client may be associated with a different file size limit. For example, client  500  is limited to files less than 2 megabytes and client  550  may handle files up to 20 megabytes. Therefore, both requests cannot be satisfied through one transfer transaction when the revision file is greater than 2 megabytes. In one embodiment, a priority bit is associated with each requesting client to establish the order in which the requests are satisfied. 
   The requests are satisfied by synchronizing the revision file with clients  500 ,  550 . The revision file may be synchronized with clients  500 ,  550  in one transaction or through a series of multiple transactions depending on the size of the revision file. Each client  500 ,  550  determines that the request is satisfied when the entire revision file is synchronized. Client  540  may purge the requested data because the requests are satisfied. Client  540  may later poll server  530  to determine if any additional requests are waiting to be satisfied. 
     FIG. 6  illustrates an operational flow diagram illustrating a process for synchronizing multiple user revisions to a shared object. The process begins at a start block where many users are authorized to access and revise a shared object simultaneously (i.e., the peer group). The object may be any entity capable of being shared such as a file. The peer group may be identified by a peer group identifier. Different versions of the shared object are identified by corresponding GUIDs and time stamps. The time stamp identifies the time when the shared object was last synchronized with a revision. 
   Moving to block  600 , a user revises the shared object. The shared object may be revised on a server, in a local cache, or on a peer-to-peer network. In one embodiment, the revision is stored as a revision file. Proceeding to block  610 , the revision is associated with a GUID and a time stamp. The time stamp identifies the time when the user revised the shared object. 
   Advancing to block  620 , the latest version of the shared object is located. The latest version of the shared object is the version that includes the most recent revisions that are synchronized with the shared object and made available to other authorized users. The latest version of the shared object may be determined from the time stamps and GUIDs associated with different versions of the shared object. 
   Transitioning to decision block  630 , a determination is made whether any conflicting revisions exist. Revisions may conflict when different users revise the same content container. The revision cannot be synchronized with the shared object if conflicting revisions exist. If conflicting revisions exist, processing continues at block  640  where the conflicting revisions are reconciled and merged (as discussed with reference to  FIG. 7 ). If no conflicting revisions exist, processing continues at block  650  where the revision is synchronized with the shared object such that other users may view the revision. Processing then terminates at an end block. 
     FIG. 7  illustrates an operational flow diagram illustrating a process for reconciling and merging conflicting multiple user revisions to a shared object. The process begins at a start block where more than one user has revised the same content container in a shared object. A conflict results when one of the revised content containers is synchronized with the shared object such that any other revisions to the content container cannot be synchronized. 
   Moving to block  700 , the conflicting revision is displayed on a conflict page. The conflict page resembles the corresponding master page except that the conflicting revision is highlighted and displayed in place of the synchronized revision. 
   Proceeding to block  710 , a conflict indicator is displayed on the master page of the shared object. The conflict indicator may be a drop down menu, a tab, or any other mechanism that informs a user that a conflict page is available for the master page. The conflict indicator for a conflict page associated with a particular user may be distinct from the conflict indicator for conflict pages associated with other users such that a current user may quickly identify the conflict pages generated by the current user. 
   Advancing to block  720 , the conflict page is displayed alongside the master page when the conflict indicator is selected. The user is presented with both the synchronized state of the master page and the corresponding conflict page. 
   Transitioning to block  730 , the user reconciles and merges the conflicting revisions into the master page. In one embodiment, the user may select the content container such that the content container is merged with the master page. In another embodiment, the user may directly implement revisions onto the master page. In yet another embodiment, the user may identify conflicting revisions as irrelevant. 
   Continuing to block  740 , conflicting revisions that are identified as irrelevant are purged. In one embodiment, conflicting revisions may be identified as irrelevant by a user. In another embodiment, conflicting revisions may be automatically identified as irrelevant. For example, a user may have synchronized several revisions with the master version of the shared object located on a server while ignoring any corresponding conflict pages. The older conflict pages that the user did not reconcile are identified as irrelevant after a predetermined time period has elapsed. Processing then terminates at an end block. 
     FIG. 8  illustrates an operational flow diagram illustrating a process for synchronizing multiple user revisions to a shared object. The process begins at a start block where different versions of shared object are stored in different locations throughout a system. Moving to block  800 , the shared object is downloaded from a store to a client. 
   Proceeding to decision block  810 , a determination is made whether the shared object is the current version of the shared object. If the shared object is the current version of the shared object, processing terminates at an end block. If the shared object is not the current version of the shared object, processing continues at block  820 . The shared object may not be the current version because the most recent revision to a content container of the shared object is not available from the store. 
   Advancing to block  820 , a request tag and client information are assigned to the store to indicate that the client requires the most recent revision data to update the shared object. The client information may include a GUID that identifies the requesting client and a time stamp that identifies the time when the client requested the current version of the shared object from the store. 
   Transitioning to block  830 , the current version of the shared object is received at the store. The store may receive the current version of the shared object when another client accesses the store with the most recent revision data. The requesting client is informed that the current version of the shared object has been received by the store. Continuing to block  840 , the current version of the shared object is synchronized with the requesting client. Processing then terminates at the end block. 
     FIG. 9  illustrates an operational flow diagram illustrating a process for seamlessly transitioning from asynchronous to synchronous communication modes. The process begins at a start block where a peer group is established that identifies users who are authorized to access a shared object. 
   Moving to block  900 , a client accesses the shared object on a server. The client is automatically connected to other clients that are also accessing the shared object (i.e., the peer group). The shared object is associated with a manifest file. The shared object includes a unique location identifier that identifies the location where the corresponding manifest file is stored in the system. 
   Proceeding to block  910 , the manifest file is retrieved from the location identified by the unique location identifier. The manifest file identifies the locations where other versions and instances of the shared object are stored within the system. The manifest file includes a peer group identifier for the peer group where a version of the shared object is stored. 
   Advancing to block  920 , a peer-to-peer network is established when any other client in the peer group accesses a version or instance of the shared object identified by the manifest file. Thus, the client may disconnect from the server and continue to access the shared file on the peer-to-peer network. Processing then terminates at an end block. 
     FIG. 10  illustrates an operational flow diagram illustrating a process for seamlessly transitioning from synchronous to asynchronous communication modes. The process begins at a start block where a peer-to-peer network is established between at least two users who are authorized to access a shared object. 
   Moving to block  1000 , a client accesses the shared object on the peer-to-peer network. The shared object is associated with a manifest file. The shared object includes a unique location identifier that identifies the location where the corresponding manifest file is stored in the system. 
   Proceeding to block  1010 , the manifest file associated with the shared object is retrieved from the location identified by the unique location identifier. The manifest file identifies the locations where other versions and instances of the shared object are stored within the system. Advancing to block  1020 , the client connects to a server. The client determines which other clients are also connected to the server. Transitioning to block  1030 , the client identifies other clients that are authorized to access the shared object from the peer-to-peer network. Continuing to block  1040 , the client connects to an authorized client when the peer-to-peer network is unavailable. Processing then terminates at an end block. 
   The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.