Image server synchronization

A package of local files are maintained in a first local computing device and a descriptive record of the local files is maintained in a second local computing device. A directory-modified-date parameter within the first local computing device and a file-modified-date parameter in the second local computing device, but updated in accordance with a local clock from the first local computing device, are used to maintain the descriptive record in the second local computing device synchronized with changes to the local files in the first local computing device. Copies of the descriptive record and package of local files are maintained in a remote computing system. A first package-modified-date, PMD, parameter in the second local computing device and a second PMD parameter in the remote computing system are used to maintain the copies in the remote computing system synchronized with those in first and second local computing devices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a computer system architecture for synchronizing changes to a package of files on a first computing system with index data, or database, on a second computing system that maintains data descriptive of the package of files. The present invention also relates to a computer system architecture for synchronizing two remote, and independent, computer servers intended for maintaining duplicates of each other's files.

2. Description of the Related Art

In computing networks where a first machines is used to maintain a database, or index data, of a plurality of files stored in one or more other machines, it is important that the data in the database accurately reflect the current state of the plurality of files stored in the other machines. That is, changes to the files stored in the other machines should be accurately reflected in the database stored in the first machine. This is especially true when the first machine is used as an interface for a network server and its job is to provide accurate information of, and access to, the files stored in the other machines. Such a network server architecture may be used, for example, to implement a an image server system.

As it is known in the art, an operating system often assigns an updated time-stamp to a file when the file is modified. Thus, one way of reducing the amount of mismatch between the database in the first machine and the image files stored in the other machines is to store each file's modified time-stamp along with other characteristic data for each file in the database. In this manner, the database can determine if its stored characteristic data associated with a specific file is accurate by comparing the file's stored time-stamp with the stored file's actual modified time-stamp. This approach, however, requires that the database implement a separate time-stamp comparison for each file, which can considerably slow down a system if the number of files is high.

Additionally, since the image files are stored in separate machines, it is possible to update, erase, or add files to the other machines without informing the first machine that maintains the database. In this case, if a new file is added, the database will have no way of knowing of the change unless it is explicitly informed of the addition. This is because the database's only method of synchronizing itself with the stored image files is through the use of each file's previously stored modification time-stamp. But if a new file is added to one of the other machines, then no data regarding the new file is yet stored in the database, and the database can thus not discern any changes. The database therefore remains ignorant of added new file.

This is also the case with other simple changes such the renaming of a file. Unless the database is explicitly informed of the change, it will have no way of synchronizing itself to the change.

The prior art thus requires that the database be explicitly informed of any changes to the stored files, on a change-by-change basis. Furthermore, the database itself has no way of identifying some types of changes, as recited above, and will thus remain ignorant of those types of changes if the communication link between the database and an other machine in which the change takes place is broken such that the other machine is not able to inform the database of the change at the time the change takes place.

This synchronization problem is exacerbated as the database itself is copied onto multiple remote servers. The database may, for example, be part of a local server, and the other machines on which the files are stored may likewise be local to the local server. The local sever may provide remote users access to the stored image file through a networks such as the internet. However, in cases where the number of remote users, or the distance between remote users and the local server is large, access to the image files may be slow.

In such cases, it is often useful to have an additional remote database network to help service the remote users. The remote database network acts as a mirror site, and consists of a remote database having a remote index of files stored on remote servers that hold copies of the image files. However, It is possible to independently alter files on either the local server or the remote servers. Therefore, it becomes more difficult to assure continuity between the local server, which maintains the local database network, and the remote database network of the remote servers. This problem is exacerbated in cases where no direct link is maintained between the local database network and remote database network such that the local and remote networks cannot inform each other of changes as they occur. Additionally, since the local and remote networks do not maintain a constant communication link with each other, they each execute their computing tasks independently according to their own respective local clocks. This further complicates the synchronizing of changes among the multiple servers since they do not have a common clock reference with which to track changes by comparing time stamps of file modifications with independent clocks. In other words, since the remote servers function independently, and each may be in different time zones, the modification time-stamp associated with a file modification cannot be directly compared to determine which server has the most recent version of a file.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a file organization system that the permits a database on a first computing device to synchronize itself with changes to a an associated file package in another computing devices without requiring that the database be notified of modifications to the file package on a change-by-change basis.

It is another object of the present invention to provide a file organization architecture wherein a database itself can identify the addition or renaming of files in an associated file package.

It is yet another object of the present invention to provide a file organization system wherein multiple remote servers can determine among themselves which of them has the most recent version of a file package, and thereby update any remote server that does not have the most recent version of the file package.

SUMMARY OF THE INVENTION

The above objects are met in a file organization system having two aspects to its architecture. A first aspect provides a File-Modified-Date (FMD) parameter and a Directory-Modified-Date (DMD) parameter used for synchronizing changes made to a file package (i.e. a collection of files) stored in a first computing device with an associated database, or index data, maintained in a second computing device. A second aspect of the invention assumes that the first and second computing devices are part of a local, first file server, and provides a first Package-Modified-Date (PMD) parameter stored within the first file server and associated with a specific file package, and provides a second Package-Modified-Date (PMD) parameter stored in a second database maintained in a remote, second file server. The first and second PMD parameters permit the local file server and the remote file server to synchronize their respective databases and associated file packages.

In the following summary, it is assumed that the local server includes a first computing device for storing the collection of files that constitute the file package, and also includes a second computing device on which is maintained the database, i.e. index data or data record, associated with the file package. It is to be understood that the file package and data record may be stored in any of many data storage devices, such as a hard drive, IC memory (i.e. flash, eeprom, eprom, dram, sram, etc.), optical-magnetic recording media, or other type of computing readable medium.

Each file package consists of a plurality of files and has associated with it a Directory-Modified-Date, DMD, parameter that is updated according to the first computing device's local clock each time the file structure of the file package is altered. For example, the DMD parameter may be updated each time a file in the file package is renamed or deleted, or each time a new file is added.

Each data record associated with a file package includes a File-Modified-Date, FMD, parameter updated under different conditions. If a file in a file package is amended, then the FMD parameter of the associated data record (which is located in the second computing device) will be updated in accordance to one of either the local clock from the first computing device or, more preferably, the local clock from the second computing device.

When a local synchronization routine is initiated to synchronize the data record with its associated file package, their respective PMD and FMD parameters are examined to determined which indicates a more recent change. If the FMD parameter indicates a more recent change, then no further updates are necessary. If the DMD parameter indicates a more recent change, then the first computing devices updates the data record in the second computing device. Furthermore, the FMD parameter in the second computing device made equal to the DMD parameter from the first computing device.

As stated above, a Package-Modified-Date (PMD) parameter is used to synchronize data records and file packages among multiple file servers. For example, it is assumed that the above described first computing device and second computing device constitute a local file server. Copies of their data record and file package are maintained in a remote file server that has access to the local file server via a network link, such as the internet. The local file server has a first PMD parameter, i.e. PMD_1, and the remote file server has a second PMD parameter, i.e. PMD_2.

In the present file organization system, updates to a data record resulting from a synchronization routine with its local file package (such as between the above described first and second computing devices) are identified as a “local synchronization routine”, and updates to a data record resulting from a synchronization routine between the local file server and the remote file server are identified as a “remote synchronization routine”. Each file server updates its respective PMD parameter in accordance with its respective local clock in response to a change to its respective data record resulting from a local synchronization routine with its local file package. Furthermore, each file server may include multiple “data record”-to-“file package” pairs. In one embodiment, each file server has only one PMD parameter, which is updated every time any of its “data record”-to-“file package” pairs is updated. In this manner, its PMD parameter would always correspond to the most recent change to any of its “data record”-to-“file-package” pairs. In an alternate embodiment, each file server maintains a separate PMD parameter per “data record”-to-“file package” pair, and can thus executive a separate remote synchronization routine for each “data record”-to-“file package” pair.

In either of the above embodiments, when either of the local or remote file server initiates a remote synchronization routine, their respective PMD parameters are examined. Whichever PMD parameter indicates a more recent change, is assumed to have the correct version of the “data record”-to-“file package” pair under test. The file server that has the correct version of the “data record”-to-“file package” pair under test then updates the “data record”-to-“file package” pair in the other file server.

At the end of the remote update, the file server that had its “data record”-to-“file package” pair updated also updates its PMD parameter. In the preferred embodiment, the PMD parameter is updated by being made equal to the PMD parameter from the other file server, which housed the correct version of the “data record”-to-“file package” pair. Alternatively, however, the PMD parameter may be updated by being made equal to the current time according to its file server's local clock.

Various approaches are described in the present invention for determining which of the PMD parameter from local file server, or the PMD parameter from the remote file server, indicates the most recent change to its corresponding “data record”-to-“file package” pair. In a first approach, the local server sends a first test-time-stamp according to its local clock along with its PMD_1parameter to the remote file server. Similarly, the remote file sever sends a second test-time-stamp according to its local clock along with its PMD_2parameter to the local file server. Each file server then identifies an offset-time as the difference between its local time as determined by its local clock and the test-time-stamp received from the other file server. For example, the remote file server would identify an offset-time as the difference between its local time and the received first test-time. Alternatively, the remote file server may identify the offset-time as the difference between the second-time stamp and the first-time stamp. The identified offset-time is then added or subtracted, as appropriate, to one of the PMD parameters (such as PMD_1) to shift it to the same timing reference as the other PMD parameter (i.e. PMD_2in this case).

Alternatively, each file server may determine a period-since-last-change time by taking the difference between its local time according to its local clock and its own PMD parameter. The file servers then exchange period-since-last-change time values. The file server with the shortest period since its last change to its PMD parameter is assumed to have the most recent “data record”-to-“file package” pair, and upgrades the other of file server.

Alternatively, the local and remote file servers may designate the local clock resident within one of local and remote file servers (or a some other clock accessible to both file servers on the network) as a master reference clock. In this case, both the local and remote file servers update their respective PMD parameters in accordance to the designated master reference clock in response to both a local and remote synchronization routine. In this way, the PMD parameters of all file serves will be based on the same master clock in spite of each file server having a different local clock.

As explained before, in all of the above embodiments, it is preferred that each file server update its corresponding PMD parameter according to its local clock in response to its file record being updated during a local synchronization routine. In the above example, during a remote synchronization routine, the file servers that has its file record updated sets its PMD parameter equal to the PMD parameter that is determined to have the most recent “data record”-to-“file package” pair.

In still an alternate approach, both the local and remote file servers may determine which of them has the most recent “data record”-to-“file package” pair by comparing their respective PMD parameters directly. The file server having the most recent PMD parameter, is designated as having the most recent “data record”-to-“file package” pair, and it updates to other file server.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIG. 1, a file organization system in accord with the present invention preferably includes a database organizer, identified as database organizer_1, for maintaining a descriptive record of a plurality of local files. Database organizer_1is shown implemented in a first computing device C1while local files pk1_file_1through pkn_file_m are illustratively maintained in a storage space within a second computing device C2. Alternatively, both the local files and their corresponding descriptive record, i.e. its corresponding database organizer, may be resident within a single computing device.

In the presently preferred embodiment ofFIG. 1, the local files are arranged into multiple file packages, package_1through package_n. Each file package may, for example, be implemented as a directory, or file folder, in which a plurality of local files are stored. For example, package_1may designate a directory in which are stored local files pk1_file_1through pk1_file_i. Similarly, package_2may likewise be implemented as a directory in which are stored local files pk2_file_1through pk2_file_k, and so on through package_n, which holds local files pkn_file_1through pkn_file_m.

In the present illustrative example, each of package_1through package_n contain a collection of image files. It is preferred that the image files within each package have a related theme, but this is not critical to the invention. In addition to the related image files, each package preferably includes a thumbnail representation file corresponding to each image file. As it is known in the art, a thumbnail representation file is a reduced (in size and quality) representation of a larger, image file, and thereby provides a quick reference to its corresponding larger image file while requiring less storage space and less image processing time.

Second computing device C2has its own local clock CK2used to keep track of changes to its resident file packages. For example, each of package_1through package_n includes a Directory-Modified-Date, DMD, parameter for storing a date stamp, as determined by clock CK2, corresponding to the most recent file structure modification of each package. For example, DMD_1of package_1receives an updated time-stamp each time any of its corresponding local files (pk1_file_1through pk1_file_i) is deleted or renamed, or each time a new file is added to, or removed from, package_1. Thus, DMD_1maintains a time stamp corresponding to the most recent change to the file structure within package_1. Further preferably, every time DMD_1is updated, second computing device C2determines the cause of the updated DMD_1time stamp. If DMD_1was updated due to an image file being renamed, then the image file's corresponding thumbnail file is renamed accordingly, or otherwise modified to maintain its association with the renamed image file. Alternatively, if DMD_1was updated due to an image file being deleted, then the deleted image file's corresponding thumbnail file is likewise deleted. Similarly, if DMD_1was updated due to a new image file being added to package_1, then second computing device generates a new thumbnail representation file corresponding to the newly added image file, and incorporates it into package_1.

Each of package_2through package_n have a corresponding Directory-Modified-Date, DMD_2through DMD_n, that is updated to the current time according to clock CK2in response to similar modifications to their respective file structure.

As stated above, database organizer_1in first computing device C1maintains a descriptive record of the local files stored in second computing device C2. Since second computing device may organize the local files into multiple file packages, i.e. package_1through package_n, database organizer_1preferably maintains a separate descriptive record D1though Dn, one for each of respective file packages, package_1through package_n. Each descriptive record, D1through Dn, preferably maintains similar information regarding its respective file package, and therefore only descriptive recorder D1is described in detail with the understanding that descriptive records D2through Dn are similarly organized.

Descriptive record D1maintains information regarding local files within package_1. For example, descriptive record D1may store the file name, file size, file type, and other data as required, corresponding to each of files pk1_file_1through pk1_file_i. Additionally, each of descriptive records D1through Dn include a respective File-Modified-Date, FMD, parameter corresponding to a time stamp supplied by second computing device C2and used as an estimation of the time at which the latest modification to a files within a corresponding file package took place.

In a first preferred embodiment of the present invention, there is only one FMD parameter for each file package, such that the FMD parameter corresponding to the time stamp identifying the most recent modification to any of the files within a file package. In a first arrangement, the FMD parameter would be updated every time any file is modified. In a second arrangement, the FMD parameter is updated during the execution of a synchronization routine, and is not necessarily assigned a time-stamp corresponding to the modification of a file. Instead, the FMD parameter is made dependent on the DMD parameter, as explained more fully below.

In one of the preferred embodiments, a descriptive record's FMD parameter may be updated only in response to a synchronization request, which may originate from first computing device C1or second computing device C2. In an alternate embodiment, the synchronization request may be instigated by either database organizer_1or any of the file packages, i.e. package_1through package_n. In either case, it is preferable that the synchronization of a file package and its corresponding descriptive record be implemented on an one-to-one basis.

When it is desired to coordinate the content of descriptive records D1to Dn with their corresponding file package, package_1to package_n, one of first or second computing devices C1and C2initiates a synchronization routine. Preferably, the synchronization routines are targeted such that each instigation of the synchronization routine may designate one, specific descriptive record and its corresponding file package. For example, if second computing device C2initiates a synchronization routing designating descriptive record D2, the first computing device sends parameter FMD_2to second computing device C2, and the second computing device C2sends parameter DMD_2to first computing device C1. FMD_2is compared with DMD_2, and if it is found that FMD_2is more current than DMD_2, then no further synchronization is required. However, if DMD_2has a more recent data stamp than FMD_2, then descriptive data D2undergoes an updated sequence.

Several update sequences are contemplated within the scope of the present invention. The objective of the update sequence is to assure that the descriptive data D2corresponds correctly to the current state of local files pk2_file_1to pk2_file_k within package_2. In a first update sequence, second computing device C2sends file structure information of all file packages to first computing device C1. The file structure information may includes the name, size, and type description for all of its local files within each package, such as files pk2_file_1through pk2_file_k in package_2. Database organizer_1then generates new descriptive data corresponding to the received data.

In an alternate preferred embodiment, whichever of first computing device C1or second computing device C2that initiated the synchronization routine, also identifies a target file package for updating. In the present example, file package_2would be identified. Second computing device C2then sends the file structure information of the target file package to first computing device C1. Database organizer_1responds by updating the descriptive data, or generating new descriptive data, corresponding to the target file package.

With reference toFIG. 2, an alternate embodiment of the present invention provides multiple local computing devices, C2and C3, for storing files packages, all in communication with the same database organizer_1in computing device C1. All elements inFIG. 2similar to those ofFIG. 1are identified by similar reference characters and are described above. In this alternate embodiment, second computing device C2stores only one file package, i.e. package_1, while a third computing device C3stores package_2through package_n. It is to be understood that it is equally possible to have each file package stored in a separate computing device, or multiple file packages stored in a plurality of computing devices.

This present embodiment functions substantially similar to the embodiment ofFIG. 1described above with the exception that Directory-Modify-Date parameters DMD_2through DMD_n are dependent on CK3, the local clock of third computing device C3, while parameter DMD_1is dependent on the CK2, the local clock of second computing device C2. Each of computing devices C2and C3can initiate a synchronization routine with database organizer_1in first computing device C1. however, it is preferred that each of second C2and third C3computing devices be able to initiate a synchronization routine only for the respective file packages that they house. For example, second computing device C2can initiate a synchronization routine identifying package_1as the target since package_1is resident within computing device C2. Similarly, computing device C3can initiate a synchronization routine for any of the file packages resident within itself. That is, computing device C3may initiate a synchronization routine for any of file package_2through package_n.

The Directory-Modified-Date parameter within each file package is updated to the current time according to the respective local clock of the computing device within which the file package is stored. For example, DMD_1within package_1is updated in accordance with clock CK2, which is within second computing device C2. Similarly, DMD_2through DMD_n, which reside within third computing device C3, are updated in accordance with CK3, the local clock within third computing device C3. Since any synchronization of a file package_1through package_n with its corresponding descriptive data D1through Dn is done on a one-to-one basis, it is not necessary that all file packages use the same reference clock. For example, if database organizer_1initiates a synchronization routine for descriptive data D2(corresponding to package_2in third computing device C3), then corresponding File-Modified-Date parameter FMD_2is compared only with DMD_2, and any updates of FMD_2are in accordance with clock CK3.

It should be noted that in bothFIGS. 1 and 2, first computing device C1has its own local clock CK1, and database organizer_1includes a Package-Modified-Date, PMD, parameter identified as PMD_1. First computing device C1uses clock CK1for its normal processing tasks, and for updating, under criteria explained below, Package-Modified-Date parameter PMD_1with a current time-stamp in accordance with clock CK1.

Preferably database organizer_1and file packages package_1through package_n are available on a network, and database organizer_1controls the access to any of file packages, package_1through package_n, on the network. Further preferably, the network is the internet.

As it is known in the art, a larger number of users attempting to access a single server can slow down the server. As it is further known in the art, the internet has a large number of users that can potentially slow down database organizer_1if too many users attempt to access it at the same time. To mitigate this issue, it is known to provide multiple servers, each having copies of the available files, and to distribute the user load across the multiple servers.

The present invention contemplates such an approach, and further contemplates that the multiple servers be distributed across a large geographic area. This can lead to a complication. As it is explained above, any of the computing devices that store the local files (C2and C3in the embodiments ofFIGS. 1 and 2) can update, edit, delete, or augment its collection of local files. Since each of the multiple servers would ideally include its own database organizer having access to its own copies of local files stored in its own local computing devices, it becomes difficult to assure that all servers maintain exact copies if the local files if each server's local computing devices can be updated independently.

Using simple date stamps identifying the date of each file's last update is not a viable solution since each computing device has its own local clock, and it cannot be assured that all the local clocks will be synchronized. Further complicating the present problem is that the multiple servers may be distributed across multiple time zones such that even if two separate servers are updated simultaneously in different time zones, each will produce a different time stamp for the update.

The Package-Modified-Date parameter is used to address the present problem of how to synchronize multiple image servers that do not share a common local clock.

With reference toFIG. 3, first computing device C1, from the embodiment ofFIG. 2, is shown in communication with a fourth computing device C4via a network13. All elements similar to those ofFIG. 2have similar reference characters and are described above. As in the case ofFIG. 2, first computing device C1is shown having direct access to second computing device C2, which holds at least one package of local files, i.e. package_1a. Similarly, fourth computing device C4functions as a second database organizer and maintains a descriptive record of local files in a fifth computing device C5, to which C4has direct access. The local files in C2are illustratively labeled package_1aand the local files in C5are illustratively labeled package_1b, and package_1aand package_1bshould ideally be duplicates of each other. That is, package_1aand package_1bshould hold identical local files. In this way, either of database organizer_1in C1or database organizer2in C4can service file requests from a remote user15.

Since remote user15may communicate with either of database organizer_1or database organizer_2to access file package_1(identified as package_1ain C2and as package_1bin C5), and neither of package_1anor package_1bis designated as a master copy of package_1it is important to synchronize the contents of package_1aand package_1b. However, both of package_1aand package_1bmay be edited independently, and thus it can be difficult to synchronize the two.

To address this problem, both database organizers incorporate a Package-Modified-Date parameter, PMD_1in C1and PMD_4in C4. In a first embodiment, PMD_1is dependent on CK1, the local clock within C1, and PMD_2is dependent on CK4, the local clock within C4. The Package-Modified-Date parameter within either of C1and C4is updated under various conditions described below, and is used to help synchronize package_1awith package_1b.

In a first approach, each of first and second computing devices C1and C4have previously updated their respective PMD parameter in response to their respective database organizer being updated during a local synchronization routine with their respective local file package (i.e. package_1aor package_1b). As explained above, C1communicates with C2to maintain its database organizer_1synchronized with changes to file package_1a. In a similar manner, C4communicates with C5to maintain its database organizer_2synchronized with changes to file package_1b. Each time database organizer_1is updated to synchronized itself with file package_1ain a manner to that described above in reference toFIGS. 1 and 2, parameter PMD_1is updated with a time stamp as determined by CK1. Similarly, PMD_2is updated with a time stamp as determined by CK4each time database organizer_2is updated to synchronize itself with package_1b(or other local file package, not shown) in a manner as described above in reference toFIGS. 1 and 2.

Any database organizer may initiate a database synchronization routine with any other database organizer via network13. If either of database organizer_1or database organizer_2initiates a database synchronization routine with the other, the two database organizers exchange PMD parameters. The database organizer whose PMD time stamp is the most recent, is assumed to have the most up to date version of the file package in question (package_1in the present case). For example, if PMD_1is a more recent time stamp than PMD_2, then database organizer_2is updated to match database organizer_1. Various factors, such as different time zones, may affect the determination of the most recent PMD parameter, and various methods for addressing these factors are contemplated within the present invention, as is explained more fully below.

Assuming that PMD_1indicates a more recent update than PMD_2, then the updating of database organizer_2may be accomplished in one of several ways. In a first approach, database organizer_1sends to database organizer_2the descriptive record of file package_1a. Database organizer_2then compares the received descriptive record with that of package_1b. Differences are noted and updated. All files in package_1bthat had their respective descriptive record updated are themselves updated in accordance with the received descriptive record. That is, they are either deleted if they are not shown in the received descriptive record, or they are replaced with corresponding files transferred from database organizer_1via network13to database organizer_2. If the files in package_1bneed to be updated, such as image files, then it is preferred that only the image files that need to be updated be transferred from via C1, C2and network13to database organizer_2and incorporated into package_1b. Any needed thumbnail images can be generated locally by either fourth computing device C4or fifth computing device C5. Alternatively, all image files from package_1acould be transferred along with their descriptive record to database organizer_2and package_1b.

As explained above, it is likely that first and second computing device, C1and C2, may have differing time references (such as being in different time zones). Several alternate embodiments are proposed to address this problem. In a first alternate embodiment, first computing device C1and fourth computing device C4exchange current time stamps (in accordance with their respective local clocks CK1and CK2) along with the initial exchange of their PMD parameter. C1will note the difference in time between its current time stamp, as determined by it local CK1, and the received current time stamp from C4, which was generated according to CK4. First computing device C1then adds the difference, positive or negative, to its PMD_1parameter to produce a temporary comparison-only PMD_1parameter, which is thereby shifted to the same time zone as PMD_2of fourth computing device C4. C1then compares the comparison-only PMD_1parameter to parameter PMD_2received from C4. In this manner, the time stamps of PMD_1and PMD_2are compared with a common time zone. Alternatively, the calculated time-zone difference can be added to, or subtracted from, PMD_2, as appropriate, instead of PMD_1to shift PMD_2to the time zone native to PMD_1. Fourth computing device C4implements a similar routine to compare its local PMD_2parameter with the received PMD_1parameter.

In still an alternate embodiment, when ever either database organizer_1or database organizer_2is updated with a new descriptive record from a remote site, it stores the new descriptive record with a current time stamp received from the remote cite and associates that time stamp with the particular remote site. Also, whenever a local computing device, such as C1, receives a new synchronization request from the a remote site, i.e. C4, (along with the data record and PMD parameter from the remote site), the local computing device C1compares the received PMD parameter from the remote site (i.e. PMD_2in the present example) with the stored PMD previously associated with that site from a previous synchronization routine. If the newly received PMD parameter is more current, than the previously stored PMD parameter, then it is assumed that the remote site, C4, must have had its local files updated since the previous synchronization routine. If the local computing device C1has not had its file package updated since the last time it synchronized itself with the remote site, C4, then it will assume that the remote site has the more current file package and permit itself to be updated with data from the remote site, C4, in a manner similar to that described above.

In the present embodiment, it is preferred that whenever either of computing devices C1or C4updates their own file package locally, they add a time stamp according to their local clock to the updated descriptive record (alternatively they may also update their respective PMD parameter according to their local clock). In this case, if the local computing device C1has updated its own file package locally since the last time it synchronized itself with remote cite C4, then it will identify a first time span (determined as the time difference between its stored time stamp corresponding to its own local update and the current time according to its local clock, CK1) and also identify a second time span determined as the time difference between the newly received remote PMD parameter (i.e. PMD_2) and the remote current time stamp from remote cite C4. If the first time span is shorter than the second time span, then it is determined the local computing device C1has the most current version of the data record and file package.

Otherwise, it is determined that the remote computing cite C4has the most current version of the data record and file package. Whichever computing device, C1or C4, is determined to have the most recent file package will update the data record and file package of the other computing device in a manner similar to that described above.

In the above examples, when ever a local machine, such as C1, is updated by a remote machine, such as C4, its PMD parameter is also updated. The PMD parameter may be updated with the PMD value from the remote machine. Alternatively, it may updated in accordance with its local clock. In all of the examples, it is likewise preferably that the PMD value of a machine be updated in accordance with its local clock whenever its any of its descriptive records (such as D1-Dn inFIG. 1) are updated. Thus, the PMD parameter of a machine will correspond to the most recent change to any of its descriptive record (i.e. D1-Dn).

It is to be understood that the routines described above for using PMD_1and PMD_2to synchronize C1and C2, may also be used to synchronize C1and C2in FIG.1. To apply the above discussion to C1and C2, one would substitute FMD_1in place of PMD_1and substitute DMD_1in place of PMD_2.

With reference toFIG. 4, an alternate architecture for synchronizing remote computing devices across different time zones and having different local clocks makes use of a dedicated reference clock31. All elements inFIG. 4similar toFIG. 2have similar reference characters and are described above. In the present embodiment, three remote computing devices C1, C4, and C5communicate with each other and with reference clock31via network13. Computing device C5has access to file package_3in its local computing device C6in a manner similar to that explained above in regards to C1/C2and C4/C3.

Reference clock31may, for example, be a freely available clock reference such as the atomic clock available from the U.S. Naval Observatory, which is freely accessible via the internet. Alternatively, it may the local clock of a designated one of remote computing devices C1to C6. In either case, when any of remote computing devices C1, C4, or C5updates itself locally, or is updated remotely, its PMD parameter is determined based on the reference clock31. In essences, the PMD parameter of all remote computing devices are synchronized to the same reference clock31. In this way, the issues associated with multiple local clocks and differing time zones are eliminated.

With reference toFIG. 5, all elements similar toFIGS. 1-3have similar reference characters and are described above. InFIG. 5, no common reference clock is used and synchronization of file packages1a,1b, and1camong remote computing devices C1, C4, and C5/C6across multiple time zones and differing local clocks is accomplished in a manner similar to that described in reference toFIG. 3above. In the present embodiment ofFIG. 5, database organizer_1and file package_1aare both incorporated into a single computing device C1such that their respective PMD and FMD parameters are both determined in reference to a single local clock CK1. Similarly, database organizer_2and file package_1bare both incorporated into single computing device C4such that their respective PMD and FMD parameters are both determined in reference to local clock CK4.