Abstract:
Generally, the described system and process enables resolution of conflicts in a synchronized folder. Within the described mesh operating environment, each of the devices may be configured to do the same processing so that the file system view of the synchronized folder looks the same on all devices (pending local capabilities). Updates that cannot be immediately realized to the local store due to conflicts may be deferred for later attempts when, for example, additional updates at the system level or local level are made to resolve or eliminate the conflict for the update item. Generally, further changes may be propagated by a user in addressing a particular conflict that the user is notified about (e.g., via a selected winner that the user disagrees with). Alternatively, the conflict may resolve itself when a further update occurs that overrides or renders moot the previous update (e.g., a deleted item having a modified enclosure, where the enclosure had a previous concurrency conflict). 
     Depending on the local file system, the described system and process may perform additional fix ups for file name, attributes, etc. In this case, the described system and process may be configured not to update a main replication feed since the updates are local or node application specific. Resolution may primarily depend on the user. When the user does resolve a conflict, the feed may be updated and the resolution propagated to all nodes.

Description:
TECHNICAL FIELD 
     The present invention generally relates to computer systems and more particularly to a computing system that manages conflicts for a set of synchronized folders. 
     BACKGROUND 
     A synchronized folder may represent a set of folders located across a plurality of nodes that are maintained to be consistent with one another. For example, each synchronized folder on each node may be consistent (e.g., same sub-folders, same folder organization, same files, etc.) with each folder of every other node. Maintaining consistency of the synchronized folder set among the plurality of nodes may be difficult enough when multiple changes are made across the set of folders. Maintaining consistency may be even more difficult in existing systems where the synchronized folder is hosted by devices running different operating environments (e.g., different applications, different operating systems, different file systems, etc.) that implement different semantics (e.g., file management and display semantics). In these situations, providing a consistent view of the synchronized folder to the local node may be more difficult because the different operating environments provide different restrictions on how items may be stored, maintained, displayed, and/or updated. 
     SUMMARY 
     The described method and system may take a series of actions to temporarily resolve at the local node some synchronization conflicts when processing an update to a set of synchronized folders. Some of the synchronization conflicts that may be temporarily resolved may arise when processing an update of the synchronized folder at a local node that implements a particular local semantic (that may be different from other nodes). Generally, the described method and system may create a special holding area folder and select winner and loser updates in handling synchronization conflicts. Winners may be displayed or otherwise made available as a selected update for a view of the synchronized folder at the local node while losers are stored in the holding area for later resolution. In some embodiments, a primary feed that provides updates to all nodes of the synchronized folder may not be modified based on the temporary fixes to any local node, thereby isolating local node processing of the updates. In some embodiments, orphan conflicts may be locally resolved by moving orphan files and folders to the holding area folder. Cycle conflicts may be locally resolved by choosing a folder with the smallest identifier and re-parenting that folder to the root. When duplicate item conflicts exist, the duplicate items may be sorted by identifier and all but the largest identifier may be moved to the holding area. All other conflicts detected by the described system may be preserved by moving unresolved losers to the holding area. The holding area may be a device level folder that may be protected from direct user access (e.g., hidden to user). 
    
    
     
       DRAWINGS 
         FIG. 1  illustrate block diagrams of a computing system that may operate in accordance with the described embodiments; 
         FIG. 2  illustrates a mesh with a synchronized folder; 
         FIG. 3  illustrates a synchronized folder system according to one embodiment of a mesh operating environment; 
         FIG. 4  illustrates a synchronization process embodiment; 
         FIG. 5  illustrates a system for managing synchronization conflicts during synchronization of a synchronized folder; 
         FIG. 6  illustrates a realization process including a conflict resolution mechanism; 
         FIG. 7  illustrates a synchronization conflict originating from an orphaned item; 
         FIG. 8  illustrates a synchronization conflict based on a cycle; 
         FIG. 9  illustrates an embodiment of a synchronization conflict resolution process for orphans; 
         FIG. 10  illustrates a process for resolving synchronization conflicts involving duplicates; 
         FIG. 11  illustrates a process for resolving synchronization conflicts involving cycles; 
         FIG. 12  illustrates a process for realizing items to a holding area; and 
         FIG. 13  illustrates a for realizing items to a main folder or local store. 
     
    
    
     DETAILED DESCRIPTION 
     Although the following text sets forth a detailed description of numerous different embodiments, it should be understood that the legal scope of the description is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims. 
     It should also be understood that, unless a term is expressly defined in this patent using the sentence “As used herein, the term ‘ —————— ’ is hereby defined to mean . . . ” or a similar sentence, there is no intent to limit the meaning of that term, either expressly or by implication, beyond its plain or ordinary meaning, and such term should not be interpreted to be limited in scope based on any statement made in any section of this patent (other than the language of the claims). To the extent that any term recited in the claims at the end of this patent is referred to in this patent in a manner consistent with a single meaning, that is done for sake of clarity only so as to not confuse the reader, and it is not intended that such claim term be limited, by implication or otherwise, to that single meaning. Finally, unless a claim element is defined by reciting the word “means” and a function without the recital of any structure, it is not intended that the scope of any claim element be interpreted based on the application of 35 U.S.C. §112, sixth paragraph. 
       FIG. 1  illustrates an example of a suitable computing system environment  100  that may operate to display and provide the user interface described by this specification. It should be noted that the computing system environment  100  is only one example of a suitable computing environment and is not intended to suggest any limitation as to the scope of use or functionality of the method and apparatus of the claims. Neither should the computing environment  100  be interpreted as having any dependency or requirement relating to any one component or combination of components illustrated in the exemplary operating environment  100 . 
     With reference to  FIG. 1 , an exemplary system for implementing the blocks of the claimed method and apparatus includes a general purpose computing device in the form of a computer  110 . Components of computer  110  may include, but are not limited to, a processing unit  120 , a system memory  130 , and a system bus  121  that couples various system components including the system memory to the processing unit  120 . 
     The computer  110  may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer  180 , via a local area network (LAN)  171  and/or a wide area network (WAN)  173  via a modem  172  or other network interface  170 . 
     Computer  110  typically includes a variety of computer readable media that may be any available media that may be accessed by computer  110  and includes both volatile and nonvolatile media, removable and non-removable media. The system memory  130  includes computer storage media in the form of volatile and/or nonvolatile memory such as read only memory (ROM)  131  and random access memory (RAM)  132 . The ROM may include a basic input/output system  133  (BIOS). RAM  132  typically contains data and/or program modules that include operating system  134 , application programs  135 , other program modules  136 , and program data  137 . The computer  110  may also include other removable/non-removable, volatile/nonvolatile computer storage media such as a hard disk drive  141  a magnetic disk drive  151  that reads from or writes to a magnetic disk  152 , and an optical disk drive  155  that reads from or writes to a optical disk  156 . The hard disk drive  141 ,  151 , and  155  may interface with system bus  121  via interfaces  140 ,  150 . 
     A user may enter commands and information into the computer  20  through input devices such as a keyboard  162  and pointing device  161 , commonly referred to as a mouse, trackball or touch pad. Other input devices (not illustrated) may include a microphone, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit  120  through a user input interface  160  that is coupled to the system bus, but may be connected by other interface and bus structures, such as a parallel port, game port or a universal serial bus (USB). A monitor  191  or other type of display device may also be connected to the system bus  121  via an interface, such as a video interface  190 . In addition to the monitor, computers may also include other peripheral output devices such as speakers  197  and printer  196 , which may be connected through an output peripheral interface  190 . 
     Generally, a mesh may be considered a set of nodes or devices that are associated with each other, intercommunicate with each other, and share resources.  FIG. 2  illustrates a mesh  200  that may be a peer to peer network where nodes of the network  201 - 204  share common services. A peer to peer configuration may be one out of many possible implementations for the mesh. Generally, software and services that enable devices and applications to run in a mesh may be called a mesh operating environment (MOE). The software and services may include application portions that run on each node and application portions that run external to each node but are available to each node via the mesh. It should be noted that a mesh device or node may be a physical device or virtual object that can participate in the mesh. 
     A file system generally includes a set of items, where an item may be a file or a folder. Files may generally be organized by folder, where the folder may represent a category in which a file is associated. A hierarchical tree structure may be formed where items are related to each other. For example, folders may include subfolders, where the folder is a parent and the subfolder is a child. A child may also be a file that is associated with a parent folder. 
     A synchronized folder  210  may represent a set of folders that are maintained to be consistent across a plurality of nodes or devices  201 - 204 . In other words, a local copy of a synchronized folder at each node may be consistent with every other local copy of the synchronized folder at every other node. Maintaining consistency of the synchronized folder among a plurality of nodes may be extremely difficult where each node may modify their local synchronized folder (e.g., a local copy of the synchronized folder) and when multiple nodes may each be required to provide a local view of the synchronized folder consistent with local node semantics. For example, in some synchronized folder systems, a synchronized folder may be hosted by devices running different operating environments (e.g., different applications, different operating systems, different file systems, etc.) that may implement different operating semantics (e.g., file management and display semantics). Different operating environments may provide different restrictions on how items of the synchronized folder may be stored, maintained, displayed, or updated. In some embodiments of the described method and system, conflicts arising from differences in local semantics may be managed (to be discussed further below). 
     Generally, updates or changes to content may be propagated using a broadcast model in which a change in the synchronized folder at one node initiates a broadcast to all nodes of the mesh of the synchronized folder to indicate the change. Synchronization conflicts may represent conflicts between different update data (e.g., originated by updates at different nodes) for the same item or related item of the synchronized folder (where an item may be a folder or a file). Other conflicts may also arise due to the capabilities of the underlying file system. 
     A portion of the described method and system may involve providing a synchronization process for the synchronized folder (or synchronized folder set). The described method and system may use feeds as a communication protocol and format to facilitate synchronization of the synchronized folder. Generally, a feed is a data format that provides users with frequently updated content. An atom feed is a type of feed used to publish frequently updated works in a standardized format. Additionally, FeedSync is an open XML implementation that is used on top of an atom feed. It should be noted that an open implementation is one whose mechanics are public and whose usage is promoted for public consumption and modification. In the system and process described herein, a file system synchronization process may be layered on top of FeedSync, where a FeedSync feed may be used to synchronize and implement a synchronized folder. 
     The FeedSync feed may be a canonical or generic format used to enable universal interoperability and communication, where node specific semantics may be addressed at the node level. Generally, file system semantics or node level application semantics may be supported in two ways. One way may be to extend semantics of the FeedSync and require that all devices/nodes conform to such a modified FeedSync semantic. Another way may be to require that devices only understand a basic FeedSync feed (representing a canonical feed) and optionally interpret file system metadata contained in the feeds for the device or node (e.g., local node level involvement). The first approach may diminish the value of using FeedSync (since customization leads to a less open standard). Hence the described system may be implemented using the second node level approach. 
     In one embodiment, the described system and process may use an atom feed with FeedSync for the synchronization process. Generally, an atom feed may be a set of items, where each item includes an attribute for referencing an enclosure (e.g., a link) and includes attributes that describe a relationship of the item with another item. The enclosure may be a link to data that represents, for example, a file. An example of a system using atom feeds is Atom Publishing Protocol or APP. This protocol may be widely used for atom feeds and some embodiments of the described method and system may implement the atom feed as APP. 
     The atom feed may be configured to include a link attribute that is used to specify a location of a enclosure. Since enclosures (files) can be of arbitrary size, they may not be present inline in the FeedSync feeds but instead may be referenced out of band (e.g., using an attribute such as &lt;link rel=“enclosure”&gt;). The implication is that enclosures may be downloaded using a separate mechanism after a feed has been synchronized. 
     Feeds allow a hierarchical structure to be captured among feed items. For example, items in the feed that contain an enclosure (e.g., a file) are allowed to have a parent item which represents a folder. Such folder items in turn can have a parent folder. Multiple top level file or folder items are allowed. To preserve hierarchical structures, the feed may include a parent ID attribute that may be used to specify a hierarchy of files and folders to store a feed&#39;s enclosures on a device. This attribute, if present, may be required to have the same value of an FeedSync ID attribute of some other feed entry. The other entry may represent a parent folder and may also be required to have a link sub-element with an attribute type set to “folder.” If the sub-element is omitted, the entry may manifest as a top level file or folder on a device. Multiple top level files or folders may be allowed. 
     A mesh operating environment implemented in some embodiments of the described system may be configured to set the FeedSync ID attribute. The ID attribute may be set to a new value upon creation of each item. In some embodiments, the ID values may be incrementally increasing values. In some embodiments, nothing outside the FeedSync layer and feed-level object creation is given the ability to modify or assign the id and by attributes. Because in a mesh environment these attributes may be assigned by outside applications in an unpredictable manner, the described system may be configured to ensure that applications do not begin relying upon hidden semantics of how these things happen to be assigned by MOE (i.e., via local node applications rather than mesh wide or MOE services). 
       FIG. 3  illustrates a synchronized folder system  300  according to one embodiment of a mesh operating environment. Generally, the system illustrated in  FIG. 3  may represent a portion of a larger mesh operating environment that is particularly configured to provide synchronization services. In other words, the portion represented in  FIG. 3  may represent only a portion of a larger MOE system including additional system services and communications and nodes. 
     Devices  301 - 303  may be nodes of a mesh that are interconnected to each other. In some embodiments, the nodes  301 - 303  may be implemented by a peer-to-peer network as known by those skilled in the art. System  300  illustrates a storage service and enclosure lookup service component  305  that may provide a set of feeds to the nodes of the mesh as well as an enclosure locator service. System  300  may also include a notification service  307  the provides indications of updates or changes in a feed. 
     In some embodiments, enclosures reference by items may be synchronized from the storage service. In some embodiments, enclosures referenced by items may be synchronized peer-to-peer. Devices generally synchronize their feeds (and thus the items within) only with the Storage Service. The Storage Service may store all feeds of all items of the synchronized folder. 
       FIG. 4  illustrates a synchronization process embodiment. At block  401 , an item in a feed is updated (or created) on a device or node. MOE may sense that this item is updated (or created)  402 . The sensing may be performed, for example, using a watcher component. A watcher component may be a monitoring component that is configured to receive update indications from a node of the mesh and facilitate alerting other nodes of the mesh about the update. The watcher component may further be configured to facilitate the update process by executing certain functions. The watcher may provide indications of updates along with the content of an update using feeds, such as an atom feed. 
     In some embodiments, the node may be configured to transmit a change or update indication to the storage service component when a change or modification has been made to the synchronized folder (e.g., a folder or item has been updated, moved, or deleted) of the local node. The watcher may be implemented as part of each node of the mesh or part of a service or both. 
     Node updates may be received at the storage service at block  403 . The storage service may use FeedSync attributes to determine what changes should be brought up to the service, and logically pull those device-side changes MOE into the storage service. Note that although this process may logically appear to be a service-side pull, the retrieval may in fact be implemented via a device-side push because from a security perspective the service may not have permission to actually pull changes from the client. When the Storage Service “pulls”, the Storage Service may receive a batch of updates with only portions of the updated feed that have been changed since the last time the service-based copy of the feed was updated by this device. This state, or knowledge (semantics defined by FeedSync rather than a node level application), may then be stored on the service (e.g., one entry for each mesh device). Each entry may contain state for a direction of data: a client pull direction and a service pull direction. 
     The Storage Service may merge the item changes into its feed at block  404 . For example, the update data is merged with a storage service copy of the feed to result in an updated feed. 
     The update of the local feed may initiate generation of a notification that may be enqueued to the notification service at block  405  for processing. At block  406 , the Notification Service may inform other devices that updates are available and may prompt nodes to pull changes down. Because the system implements a feed service, devices that come online (e.g., connect with the mesh) may receive updates once they subscribe for the notifications. 
     In some embodiments, the Storage Service&#39;s feed policy may specify that enclosures are to be uploaded to the Storage service before notifications are sent to other clients. This may help ensure that the client sourcing the enclosure will not be flooded with dozens of simultaneous upload requests that might hurt upload bandwidth. In some embodiments that implement quota constraints or for large client-side folders, the Storage Service may not attempt to upload enclosures. 
     Devices may use the same FeedSync algorithm to pull down changes (e.g., just the new updates) from the Storage Service and merge the changes or updates into their local copies of the feed at block  407 . Nodes may realize the new feed or updates at block  408 . Devices may also locate and replicate enclosures over if required at block  409  (whether from peers or from the Storage Service, as illustrated in  FIG. 3 , depending upon communications topology and where it&#39;s dynamically determined to be best to retrieve the enclosures). 
     Managing Conflicts During Synchronization of a Synchronized Folder Set 
     Processing of a feed received from the Storage Service may be performed in two blocks. The update items in the feed from the Storage Service may be merged with a local copy of the feed at a node. In one embodiment, merging the feed data may include associating or matching each item of the feed with corresponding items of the local feed copy based on an identifier of each item. In one embodiment, merging updates with the local feeds includes modifying the local feed to incorporate the updates. This may include overriding local feed information with the updates. In the described system, where the updates are incremental updates, the local feed may simply be updated to incorporate only the most recent changes. 
     Enclosures may then be downloaded and stored as files in a temporary directory. The enclosures may be made available to a local view of the file system (e.g., a view of the local copy of the synchronized folder). 
     It should be noted that a view of the synchronized folder may be implemented as a view store (which may be called a local folder) separate from a store containing a main feed, where the view store may contain just the items that of the synchronized folder that are available for access/viewing to an application or user. In this embodiment, the local folder view may be constructed by moving or copying realized items to the view folder. It some embodiments, the view may be implemented as a filter that only presents a subset of a main local store for viewing or access. Regardless of implementation however, the view of the synchronized local folder may be tailored by the method and system described herein so that the view complies with local operating system rules and semantics while still providing synchronized context to a plurality of nodes. 
     Generally, realization may be a process for making the updates available to a view of the local synchronized folder provided to the node applications and node user. In the described method and system, realization may include a process that handles or manages conflicts between the received update content from the feed and a previous view of the synchronized folder. A realization may check for conflicts based on the new feed and local store contents/view before releasing the new feed content to the view of the local folder for access by the user. When no synchronization conflicts exist, or when a synchronization conflict is resolved, realization may generally involve making the item available to the main folder for user or application viewing and access. Conflicts that remain unresolved may be placed in a holding area for later realization. 
     Generally, in the described system, any resolutions or fixes to the file system for orphans, duplicates, cycles, etc. may be prevented from being reflected back in the feed (e.g., the Storage Service feed may not be updated). In some embodiments, the local fixes may be prevented from being reflected back in the feed altogether. It should be noted that the realization process may be implemented as a recursive process. More specifically, the realization process may involve applying a function to all subfolders and items of a parent folder. 
       FIG. 5  illustrates a system for managing synchronized folder conflicts during a synchronization of a local folder. The system includes a holding area store  502 , a deferred items store  504 , and a local store  505 . Generally, the local store (which may be called a main folder) may be accessible by a user and may represent a view of the synchronized folder that is displayed to the user as a synchronized folder. The holding area store  504  and deferred items store  502  may be secured from user access (e.g., hidden or otherwise restricted from user access) and used in this embodiment to manage the synchronization conflicts in accordance with the described system (and will be further described below). 
       FIG. 6  illustrates a realization process including a conflict resolution mechanism. The realization process may be initiated by a number of activities or events. For example, the realization process may be initiated when an updated feed is received  601 . It should be noted that the realization process may be initiated by other activities including, but not limited to, a local node originating an update to items in the local store, initiating by a local node of enclosure downloads, etc. 
     The realization process may involve forming or retrieving a set of deferred items (block  602 ). A deferred item store may be created at block  603  to store the deferred items. The deferred item store may represent a collection of deferred items. The realization process may involve analyzing each deferred item (blocks  605 - 609 ) to detect and resolve synchronization conflicts. A deferred item may be an item of the local copy of the feed that has been updated (e.g., where an update item from the update feed was merged with a corresponding item of the local copy of the feed). The deferred items may include all items of the holding area that were placed there from previous realization processes or runs. 
     Several types of synchronization conflicts may occur in a synchronized folder system and in the described system, where the conflicts may be checked for and resolved in a recursive manner for each deferred item. 
     A synchronization conflict originating from an orphaned item is illustrated in  FIG. 7 . Generally an orphan is an item that is modified at a first node where a folder containing the item is deleted in a second node. The conflict arises as to how to update the synchronized folder when one update involves deleting a folder and where a second update involves modifying an item that belongs to that folder (there is an assumption that the item has importance since it is being modified). The item no longer has a parent folder or relations to a parent folder and thus is termed an orphan. 
     Another synchronization conflict is duplicate items or simply called duplicates. Duplicates may occur when two items or files have the same name. For example, in some nodes, a local operating system may not be capitalization sensitive (e.g., Windows NTFS) while in other nodes a local operating system may be capitalization sensitive (e.g., Macintosh Hierarchical File System). In some existing systems, a least common denominator approach may be used where the more widely accepted naming system is used (e.g., the most restrictive naming system is used). This approach, however, may involve changes at the central storage service to massage data for accommodating local views. The method and system described herein, on the other hand, may be configured to provide a local view of the synchronized folder that is consistent with local operating system semantics without modifying a source of a feed that is provided to every other node. 
     Another synchronization conflict is termed cycles, which is illustrated in  FIG. 8 . Cycles exist when an arrangement of folders is inverted, as illustrated in  FIG. 8 . Generally, when folder B is a subfolder of folder A and then folder A is modified to become the subfolder of folder B, we have a conflict that may be termed a cycle. The cycle may include the set of folders that are inverted from another set of folders. Thus, in  FIG. 8 , a cycle may include the folder set A/B where folder A is a child of folder B. 
     As illustrated in  FIG. 6 , the realization process may involve applying a set of realization functions (e.g.,  606 - 608 ) to each deferred item in the deferred item store, including an orphan resolution function  606 , a duplicate resolution function  607 , and a cycle resolution function  608 . In some embodiments, when realizing enclosures to a file system, the mesh operating environment may be configured to obey a set of restrictions at the local node. Such restrictions may generally be threefold: 
     1) a file or folder may be required not to be an orphan (unless it is top level or root level), e.g., the parent folder may be required to exist and not be a tombstone (e.g., a file marked for deletion); 
     2) file and folder names may be required not to be duplicated under a parent folder; and 
     3) the folder hierarchy may be required to not contain cycles. 
     When there are no conflicting changes, enclosures in the FeedSync feed may be clear of orphans, duplicates or cycles (to be discussed further below). It should be noted that other conflict resolution functions may be included in other embodiments. However, it may be a requirement of the described method and system that an application may resolve a synchronization conflict only in a deterministic way that would not cause further conflicts if done concurrently in parallel on a plurality of disconnected nodes. Thus, additional conflict resolution functions may be included with this restriction in mind. It should be noted that an item may be allowed to have multiple conflicts simultaneously. Also, depending on the capabilities of the node, other local restrictions (ex. case sensitivity, file name length, valid characters, valid set of file attributes, etc.) may be applied to the folder view. 
       FIG. 9  illustrates an embodiment of a synchronization conflict resolution process for orphans. In a synchronization conflict situation involving an orphan, the system may select a winner and a loser update. For example, in the orphan situation described above, one of the folder deletion or the orphan update (without folder deletion) may be chosen as the winner. The looser may be stored in a loser cache designated as the holding area. 
     In one embodiment, the described process may check a currently processing deferred item to see if the item is deleted  901  (e.g., the feed includes an item marked updated as deleted). If the item is deleted, children of the item may be searched for in block  902  and realized to the holding area at block  903 , after which the next deferred item may be selected and processed  907 . It should be noted that when searching of children, the described process and method may find a corresponding item of the local synchronized folder, a corresponding deferred item, both a corresponding item of the local synchronized folder and a corresponding deferred item, or no children. When returning a result set of a search for children, the describe process and method may prefer a deferred item (if available) over a local synchronized folder. This may be the chosen priority because the deferred item generally represents newer data. It should be further noted that the same search and priority applied with respect to retrieving orphan children may be applied to other conflict resolution processes described herein. In other words, in some embodiments, whenever a resolution process searches for a corresponding item or related item, the resolution process may find a set of deferred items and local folder items (representing what is viewed by the user). The deferred items (if they exist in the set) may be acted upon or selected for processing over the local folder items. 
     Continuing with the process of  FIG. 9 , a block  904  may determine whether the currently processing deferred item has a parent. If the item has no parent, then the next deferred item may be selected and processed  907 . If the item has a parent, a block  905  may determine whether the parent is deleted. If the parent is deleted, the current item may be moved to the holding area  906  otherwise, the next deferred item may be selected and processed  907 . The process of  FIG. 9  may represent process block  606  in  FIG. 6 . 
       FIG. 10  illustrates a process for resolving synchronization conflicts involving duplicates. For a current or selected deferred item, the system may search for all siblings of the item (or items with the same parent) at block  1001 . The system may then determine if duplicates exist within the set of siblings (if any) at block  1002  and  1003 . The system may sort any duplicates by FeedSync ID. As discussed above, FeedSync IDs may be assigned at item creation, thereby providing a sequential time stamp as to the origin of the item. Thus, the FeedSync ID may indicate the chronology of an update for a particular item. In one embodiment, the system may be configured to select the duplicate item with the largest FeedSync ID (e.g., the most recent) as a winner for moving to the local store  1004 , while sending other duplicate items to the holding area store  1005 . In some embodiments, the IDs may sequentially decrease and the ID with the smallest FeedSync ID may be selected as the winner. In some embodiments, regardless of the sequencing (whether increasing or decreasing), the winner may be chosen as the least recent item. It should be noted that a critical factor in determining the method for resolving duplicates is that the method when applied at each of a plurality of nodes, generates the same results. This may be used to ensure that each node provides the same view of the synchronized folder. 
     The process may then load the next deferred item at block  1006  and repeat the process. The process of  FIG. 10  may represent process block  607  in  FIG. 6 . 
       FIG. 11  illustrates a process for resolving synchronization conflicts involving cycles. A check may determine whether a currently processing or selected item is a folder  1101 . If the item is not a folder, then a next deferred item may be processed  1105 . If the item is a folder, folder associations may be checked to determine if cycles exist  1102 . If a cycle exists, the current folder may be realized to the holding area  1103  as well as associated folders of the cycle  1104 . 
     In cycle conflicts, both trees may need to be preserved as priority is difficult to assign to one tree versus another. In some embodiments, a synchronized folder may keep its existing structure and place the cycles in the holding area store. In some embodiments, the folder with the older time stamp (smaller FeedSync ID) may be re-parented to a root folder. The root node may be a folder that is a common parent to a cycle and its counterpart cycle. The process of  FIG. 11  may represent process block  608  in  FIG. 6 . 
     To facilitate the execution of updates from the deferred items to the local folder so as to prevent further conflicts and to maintain order of the updates so that future realization runs may resolve conflicts, a sort function  609  may be used to order the deferred items. The sort function may be configured so that every parent item that is not a tombstone has children that appear sequentially after the parent. For every parent that is a tombstone, its children may be sorted to appear sequentially before the item. In this manner add or modification updates may be performed top-down (hierarchically), while deletes are performed bottom-up. Generally, a tombstone is a placeholder indicating a delete update (e.g., a file that has been deleted by a node). 
     Another synchronization conflict is when two or more nodes attempt to update or modify one file (represented as an enclosure) of the synchronized folder where each update conflicts with the other. This situation may occur, for example, when a user at node A may modify one file while an update arrives based on a node B update to the same file. The described system may be configured to pick a winner update (or version) and a loser update, where the winner update is realized or moved to the local store while the loser update is realized to the holding area. Final resolution of this conflict may be left to the node or user. In some embodiments, a time stamp of the update feed item and local store item may be compared to determine which is newer and the system may be configured to select the newer version as the winner. The system may still, however, leave final conflict resolution to the end user. 
     A key operation feature of the described system is that the system may be configured not to automatically update the local copy of the feed (which would prompt updating the Storage Service copy of the feed) to resolve synchronization conflicts. Performing automatic updates on the feed may result in cascading conflicts or even divergence. Thus, in some embodiments of the described system, final resolution of conflicts is primarily left to the end user of the node. This means that the feeds are synchronized within the system with the orphans, duplicates, and cycles intact, and devices may be configured to be tolerant towards the presence of these conflicts (or other limitations), which are held in the holding area. 
     The described system may use the concept of ghosting or ghost files to help reduce the possibility of file synchronization conflicts. Generally, a ghost file may represent a placeholder for items (folders and files) when an item has been updated and the system is in a process of downloading or realizing that update or when an old file is available and an update is unavailable. In some systems, a zero byte placeholder file is used to represent a ghosted item while a “.ghost” file may be created to indicate a ghost display (e.g., a ghost icon). The ghosted file may alert a user that a file that the user is about to modify is already in a transition state. While there may exist narrow windows of time where ghosting may not catch a concurrency issue, ghosting may help to reduce the possibility of this conflict. For example, when a user manages to begin editing an item in a local synchronized folder before an update notification is broadcast to or received at the local node, a ghosting indication for the item may be initiated. 
     It should be noted that in some embodiments, a ghosting feature may be set by an end user. For example, to conserve disk space, a user may adjust a setting of the MOE to not download enclosures, but rather ghost them. It should be noted that ghost files may generally be configured so that they cannot be updated (as they represent only placeholders). One operation that may be allowed in some embodiments is deleting a ghost file, which may then cause deletion of the underlying file in the system (via modification of the feed). 
     Realizing the items to the holding area may involve a few process blocks further illustrated in  FIG. 12 . In realizing an item to the holding area, the item may be removed from a current realization run  1201 . This may involve removing the item from the current deferred items collection or store. A current deferred items collection may be closed from item additions until a realization run is finished (e.g., until a set of realization processes have been applied to each deferred item in the collection from a time when the processes were initiated). It should be noted that removing the item from the deferred items in this process may prevent reapplying methods related items such as child items, since the resolution methods described herein may be recursive (e.g., children of the folder may be operated on). A check may be made to determine if the item is ghosted  1202 . If the item is ghosted, the ghost files (e.g., a .ghost file and a placeholder file) implementing the ghost feature may be deleted  1203 . If the item is not ghosted, a check may be made to determine whether the current item is a folder  1204 . If the item is a folder, the method may retrieve each child of the folder  1205  and may apply to each child of the folder the realization-to-holding-area process  1206 . The folder may then be deleted  1207 . 
     If the item is not a folder, then the item may be a file. A check may be made to determine whether an update of the file is available  1208 . If a new version of the enclosure has been downloaded, the file stored in the holding area may be updated  1209 . The file may then be moved to the Holding Area  1210 . The process may be repeated for a next item  1211 . 
     A process embodiment for realizing items to the main folder, or local store, may be illustrated by  FIG. 13 . A check may be made to determine whether a current item being realized to the main folder is a folder  1301  (as opposed to a file). If the item is a folder, corresponding Create/Rename/Delete commands may be executed based on the item update  1302 . 
     If the item is a file, a check may be made to determine whether an enclosure of the file has been downloaded to the local node  1303 . If the enclosure has not been downloaded, ghost files may (e.g., icon and placeholder files) be created to apply the ghost effect or feature  1304 . A check may then be made to determine whether the file has been modified  1305 . For example, the updated file may be checked against the local store version of the file to determine if either the length/size of the file and/or timestamp is different. If the file has not been modified, the file may be moved to the holding area (e.g., while downloading enclosure)  1306 . If the file has been modified, the ghost files may be deleted  1307 . 
     If the enclosure has been downloaded or if the enclosure was realized to the holding area, a check may be made to determine whether the file has been modified  1308 . If the file has been modified, the enclosure may re-requested for download  1309 . If the file has not been modified, the ghost files may be deleted  1310 . If an error is thrown deleting the ghost files, the item may be deferred for realization  1312 . If no error occurs, the older version of the file may be deleted from the Holding Area  1313 . The file may then be moved into the main folder or local store  1314 . In some embodiments, if any further error is thrown, realization may be deferred. 
     It should be noted that the processes of  FIGS. 6 , and  9 - 13  may be implemented as a set of functions. More particularly, a function representative of the process of  FIG. 6  may call (block  610 ) a function representative of the process of  FIG. 13 . The processes of  FIG. 9-11  may call a function representative of the process of  FIG. 12 . 
     It should be further noted that the conflict resolution methods described herein generally are provided to a local view of the synchronized folder which is represented by the local store or local folder (main folder). These resolutions may not be adjusted into the feed of the Storage Service. However, when a user resolves a conflict (e.g., those stored in the holding or a current deferred item listing) that conflict may be reflected in the Storage Service feed as an update. For example, a watcher component may detect a user originated change for modification to the Storage Service.