Electrical computers and digital processing systems: multicomput – Multicomputer synchronizing
Reexamination Certificate
1999-02-26
2002-02-05
Burgess, Glenton B. (Department: 2153)
Electrical computers and digital processing systems: multicomput
Multicomputer synchronizing
C709S203000, C707S793000
Reexamination Certificate
active
06345308
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a network computer system and a method for executing a reliable synchronization process thereof. More particularly, the present invention relates to a method for performing a reliable and flexible synchronization process between a server computer and a network computer to assure that the network computer can operate in a mobile environment.
Further, the present invention relates to a method for removing inconsistency that appears between resources of a server computer and resources of a network computer when the network computer is coupled to the server computer after functioning as a mobile computer.
2. Discussion of Background
In recent years, a network computer system has been developed as a novel computer architecture. The system includes a server computer and a plurality of client computers (referred to as network computers (“NCs”)) that are coupled to the server computer through a network, such as a local area network (“LAN”).
A characteristic feature of the network computer system is that the server computer only stores resources, such as an operating system (“OS”), application programs and data for processing, and the respective network computers do not individually store these resources. On an as-needed basis, a network computer simply downloads these resources from the server computer through a network. Consequently, the network computer system has advantages of flexibility for easily updating the OS and application programs as a whole system and of reducing overall cost of the computer system in comparison to constructing the system using a large number of conventional stand-alone personal computers. Current network computer systems can operate only while the network computers are coupled to a server computer through a network, such as a LAN, as shown in FIG.
2
.
FIG. 2
depicts a network computer (
12
) that is constantly coupled to a server computer (
11
) through a LAN (
10
-
1
). When the network computer processes data, it downloads a program and data stored in the server. After processing the data, the network computer (
12
) must upload the updated data to the server in order to maintain consistency of the data. Thus the network computer must be always coupled to the server.
Recently, it has become desirable to use such a network computer as a mobile computer, i.e., off-line from the server. To use a network computer in a mobile environment, local storage is easily installed in a network computer for storing replicas of these resources, i.e., the OS, application programs and data in the server, for off-line processing by the network computer.
FIG. 3
illustrates a network computer having a mobile status capability. As discussed previously, the network computer (
12
) includes a local storage (
24
) for storing replicas of the programs and data in the server (
11
). While the network computer (
12
) is online, these resources are downloaded in the local storage (
24
) through the LAN (
10
-
1
). By using resource replicas Data (
24
-d) and Program (
24
-p) in the local storage (
24
), the network computer (
12
) processes data as if it were on-line even when the network computer is off-line from the server (
11
). Thus, the network computer (
12
) can be used as a mobile computer.
FIG. 3
illustrates an off-line network computer (
12
M). When a mobile operation is complete, the network computer is coupled to the server computer (
11
) and returns to an online state. For continuing the same operation that was executed in an off-line state, the computer system needs to perform a synchronization process to secure consistency between the updated Data (
24
M-d) in the network computer and the Data (
11
-d) in the Server (
11
). Accordingly, the updated Data (
24
M-d) in the network computer must be uploaded to the server computer (
11
).
However, there is a serious problem for performing such a synchronization process if the synchronization list in the server computer (
11
) is modified during the mobile operation of the network computer (
12
M). When a network computer processes data, as explained above, the network computer must use server resources that have been downloaded into the local storage in the network computer itself by referencing listed necessary objects in the synchronization list of the server computer. The synchronizing objects in the synchronization list of the server computer are intentionally defined and designated by a person who is responsible for controlling the system.
At an initial downloading stage of the resources from the server by referencing the synchronization list into the network computer, the downloaded data of the resource replicas into the local storage of the network computer maintain consistency with the data in the server resources. Then the network computer is logged-out from the network and attains an off-line state. While off-line, the network computer functions independently by using the resource replicas in the local storage only. Since the network computer does not access the server computer during mobile operation, it can not recognize modifications to data in the resources of the server computer made while the network computer is off-line.
However, while the network computer is off-line, it may become necessary to update or change resources in the server computer side. For example, modifications to the synchronization list or to application programs may become necessary in accordance with additions or deletions of commodities or price lists of the objects that are being handled in the system. If such a change in the server resources occurs during the mobile operation of the network computer, inconsistency between the contents of the server resources and the replica data of the network computer appears when the network computer is again coupled to the server.
When the network computer is again on-line, a synchronization process must be performed. The network computer uploads the data in the local storage that have been updated during the mobile operation to the server in accordance with the synchronizing objects that were initially designated in the synchronization list of the server. Consequently, even if an objective resource that was initially listed in the synchronization list has been deleted while the network computer was off-line, the updated data for the objective resource are uploaded to the server in the synchronization process. However, since the objective resource has already been deleted in the server computer, the data of the objective resource can not be updated even if it has been uploaded in the synchronization process.
This inconsistency between the server resources and the data in the network replicas may appear for other reasons, for example, if the contents of the synchronization objects are changed when another network computer or the application programs send a demand to change the objects. In these cases, it is necessary to avoid such inconsistencies between the server resources and the contents of the data in the network computer when the network computer has returned on-line to the server computer after it completes an off-line operation.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to solve the aforementioned problems of the conventional network computer system.
Another object of the present invention is to provide a novel network computer that can be operable as a mobile computer and a novel synchronizing method for resolving inconsistencies between server resources and resources of a network computer that appear after mobile operation of the network computer.
More particularly, an object of the present invention is to provide a network computer that is suitable for mobile usage and a method for increasing reliability and flexibility of a synchronization process that can be coordinated with a synchronization list in a server computer.
This may be accomplished by providing a network computer that includes a replica list of the synchronous list of the server computer. A meth
Benson Walter
Burgess Glenton B.
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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