Method and system for supporting off-line mode of operation and synchronization using resource state information

• US 6,578,054 B1
• Filed: 10/04/1999
• Issued: 06/10/2003
• Est. Priority Date: 10/04/1999
• Status: Expired due to Term

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Anderson, Rebecca L., Deen, Brian J., Hopmann, Alexander I.
• Primary Examiner(s): An, Meng-Al T.
• Assistant Examiner(s): Lin, Kenny
• Application Number:
  US09/412,766
• Time in Patent Office: 1,345 Days
• Field of Search: 707/201, 707/202, 707/203, 707/10, 707/8, 709/205, 709/201, 709/203, 709/204, 709/217, 711/161, 711/141, 711/144
• US Class Current: 707/625
• CPC Class Codes: G06F 16/27 Replication, distribution or synchronisation of data between databases or within a distributed database system; Distributed database system architectures therefor
• CPC Class Codes: G06F 16/273 Asynchronous replication or reconciliation
• CPC Class Codes: G06Q 10/107 Computer-aided management of electronic mailing [e-mailing]
• CPC Class Codes: H04L 67/1095 Replication or mirroring of data, e.g. scheduling or transport for data synchronisation between network nodes
• CPC Class Codes: H04L 67/568 Storing data temporarily at an intermediate stage, e.g. caching
• CPC Class Codes: Y10S 707/959 Network
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

Systems and methods for synchronizing multiple copies of data in a network environment that includes servers and clients so that incremental changes made to one copy of the data can be identified, transferred, and incorporated into all other copies of the data. The synchronization can be accomplished regardless of whether modifications to the data have been made by a client while the client is in an on-line or off-line mode of operation. The clients cache data locally as data are modified and downloaded. The caching enables the clients to access the data and allows the synchronization so be performed without transmitting a particular version more than once between a client and a server. Such elimination of redundant data transmission results in an efficient use of time and network bandwidth.

Claims

1. In a networked system including a server and a client, wherein the server stores a resource, a method of enabling a client to access the resource, comprising the steps of:

transmitting, from the server to the client, resource state information that represents the state of the resource stored at the server at a selected moment;

transmitting, from the server to the client, a copy of the resource as it exists at the server at the selected moment;

storing the copy of the resource in a local store associated with the client;

modifying the copy of the resource stored in the local store;

transmitting the modified copy and the resource state information from the client to the server;

based on the resource state information transmitted to the server, determining whether the resource stored at the server has changed since the selected moment; and

if it is determined that the resource stored at the server has not changed, replacing the resource stored at the server with the modified copy.

2. A method as recited in claim 1, wherein the local store is a nonvolatile storage device that is used as a cache.

3. A method as recited in claim 1, wherein the step of modifying is conducted by the client while the client is off-line with respect to the server.

4. A method as recited in claim 1, further comprising, after the step of replacing, the step of transmitting new resource state information to the client.

5. A method as recited in claim 1, wherein the step of transmitting the modified copy comprises the step of storing the modified copy at the local store without transmitting the modified copy from the server to the client.

6. A method as recited in claim 1, wherein the step of determining whether the resource stored at the server has changed since the selected moment comprises the step of comparing, at the server, the resource state information transmitted to the server with a current version of the resource state information, wherein the current version of the resource state information represents the state of a version of the resource stored at the client at the time of the step of comparing.

7. A method as recited in claim 6, wherein the step of comparing results in a determination that the resource state information transmitted to the server and the current version of the resource state information are the same, thereby determining that the resource stored at the server has not changed.

8. A method as recited in claim 6, wherein the step of comparing results in a determination that the resource state information transmitted to the server and the current version of the resource state information are different, thereby determining that the resource stored at the server has changed, the method further comprising the step of performing a conflict resolution operation in response to the resource stored at the server having changed.

9. A method as recited in claim 1, further comprising the step of storing, in the local store, the resource state information.

10. A method as recited in claim 1, wherein step of transmitting the copy of the resource from the server to the client is performed only once.

11. In a client associated with a networked system that includes a server that stores a resource, a method for accessing the resource and then interacting off-line with the resource in a manner such that it appears, from the standpoint of the client, that the client is on-line, comprising the steps of:

while the client is on-line with the server, receiving from the server a copy of the resource and resource state information representing the state of the resource stored at the server at a selected moment;

storing the copy of the resource in a local store associated with the client;

placing the client in an off-line condition with respect to the server; and

performing a data operation on the copy of the resource while the client is off-line by accessing the copy of the resource in the local store, the data operation resulting in a modified copy of the resource; and

synchronizing the resource stored at the server with the modified copy of the resource while the client is subsequently on-line after the step of performing the data operation, the synchronization being performed at least in part by transmitting to the server the copy or the resource stored at the client, and the resource state information.

12. A method as recited in claim 11, further comprising the steps of:

determining whether the resource stored at the server has changed since the selected moment based on the resource state information transmitted to the server; and

if it is determined that the resource stored at the server has not changed, replacing the resource stored at the server with the modified copy.

13. A method as recited in claim 11, wherein the data operation includes a read operation.

14. A method as recited in claim 11, wherein the data operation includes a write operation.

15. A method as recited in claim 11, wherein the data operation includes a delete operation.

16. A computer program product for implementing, in a server included in a network that also includes at least a first client and a second client, a method for synchronizing multiple copies of a resource that are stored at various locations in the network, the computer program product comprising:

a computer-readable medium carrying computer-executable instructions for implementing the method, the computer-executable instructions comprising;

program code means for generating resource state information that represents the current state of a resource stored at the server;

program code means for transmitting, from the server to the first client, a copy of the resource state information as it exists at the server at the selected moment and a copy of the resource as it exists at the selected moment;

program code means for receiving a request to update the resource stored at the server with a modified copy of the resource generated by the first client, the request including the copy of the resource state information;

program code means for determining whether a conflict exists in response to the request by comparing the copy of the resource state information received from the first client with the resource state that represents the current state of the resource stored at the server; and

program code means for replacing the resource stored at the server with the modified copy if it is determined that no conflict exists.

17. A computer-readable medium as recited in claim 16, wherein the computer-executable instructions further comprise program code means for performing conflict resolution if it is determined that a conflict exists.

18. A computer-readable medium as recited in claim 16, wherein the request to update the resource is encoded in an XML language.

19. A computer program product for implementing, in a server included in a network that also includes at least a first client and a second client, a method for synchronizing multiple copies of a resource that are stored at various locations in the network, the computer program product comprising:

a computer-readable medium carrying computer-executable instructions for implementing the method, the computer-executable instructions comprising;

program code means for generating resource state information that represents the current state of a resource stored at the server;

program code means for transmitting, from the server to the first client, a copy of the resource state information as it exists at the server at the selected moment and a copy of the resource as it exists at the selected moment;

program code means for receiving a request to update the resource stored at the server with a modified copy of the resource generated by the first client, the request including the copy of the resource state information;

program code means for determining whether a conflict exists in response to the request by comparing the copy of the resource state information received from the first client with the resource state that represents the current state of the resource stored at the server; and

program code means for performing conflict resolution if it is determined that a conflict exists.

20. A computer-readable medium as recited in claim 19, wherein the request to update the resource is encoded in an XML language.