The understanding of Distributed system

absrtact: distributed computer system is a kind of configuration method and corresponding function configuration method. It is a multi-processor computer system, each processor through the interconnection network to form a unified system, the original system of the CPU processing tasks distributed to the corresponding processor, speeding up the processing speed of the system, simplifying the logical structure of the host. In addition to the general characteristics of distributed systems, this paper introduces a special distributed system-computer-supported system work system (CSCW).

keywords: distributed system,CSCW

1. Defined

With the rapid development of the economy, more and more work has become very complex, with the power of a person or a computer can not be completed, the information processing capabilities of the broad and in-depth demand, distributed systems are increasingly widely recognized and widely used. The so-called distributed computer system, refers to by a number of decentralized computers, connected by the interconnection of network systems, the system of processing and control functions distributed in each computer, make full use of the resources of each computer, to accomplish a task together. A distributed system is a collection of independent computers, but for users of this system, the system is like a computer. Distributed computer systems are also referred to as distributed systems.

2. Characteristics

1. No master-slave distinction;

2. exchanging information between computers;

3. Resource sharing;

4. Collaborate with each other to accomplish a common task.

3. Role

In addition to the main functions of the single-machine operating system, distributed process communication, Distributed file system, distributed process migration, distributed process synchronization and distributed process deadlock should be included.

1. Distributed Process Communication

The process communication of distributed system is implemented by some communication primitives provided by the distributed operating system. However, because there is no shared memory in the distributed system, these primitives need to be implemented according to the conventions and rules of the communication protocol. Key concepts related to distributed process Communication include: Communication protocols, client / server operating modes in distributed environments, message delivery methods for process communication, and remote procedure invocation methods.

2. Distributed File System

A distributed File system is a system that allows users on different machines to share files through a network to interconnect. It allows all hosts running it to be shared and manages the communication between the operating system kernel and the file system.

3. Distributed Process Migration

Distributed process migration refers to the machine (referred to as the original machine) that the process originally ran to send enough information about the state of the process to the target machine (the machine to be moved to), so that the process can run on another machine.

4. Distributed Process Synchronization

In distributed systems, processors do not have shared memory and unified clocks, so distributed process synchronization must sequence the events that occur in different processors, and should be equipped with a well-performing distributed synchronization algorithm to ensure that process synchronization is less costly.

5. Distributed Process deadlock

In distributed systems, deadlocks can also be caused by processes competing for resources. The deadlock strategy discussed in a single processor system can be used for multiprocessor system as long as it is slightly modified. For example, an ordered resource allocation deadlock prevention technique can be used for distributed systems as long as there is a simple definition of a full order between system events.

4. Computer-supported collaborative work system

Now we introduce a distributed system, which is a cooperative working system (CSCW) supported by computer.

1. Defined

Computer-supported CSCW (Computer supported cooperative work) is a technology that integrates human cooperative behavior patterns with computer-supported technologies, that is, in a computer-supported environment (CS) , a group works together to complete a common task (CW)and to improve the quality and efficiency of the work of the group by creating a collaborative environment that improves the way people communicate, eliminates or reduces barriers to separation between time and space, and saves staff time and effort. Its basic connotation is computer-supported communication, cooperation and coordination. such as shared file systems provide the ability to share resources, e-mail and multimedia conferencing systems provide communication support functions between people, workflow and decision support systems for organizational management functions, etc. CSCW fully embodies the characteristics of the group and cooperation of people's work in the information age, and becomes one of the emphases of the development of information science.

2. Classification of CSCW Systems

computer-supported collaborative work can be categorized by time and space. According to the concept of time, can be divided into synchronous and asynchronous mode, according to the concept of space, can be divided into local and offsite. This allows you to divide the computer-supported collaborative work into four categories:

1. Synchronization mode: The same task at the same time, the same way of cooperation, such as joint decision-making, co-editing,CAD, indoor meetings and so on.

2. Distributed synchronization mode: co-design, joint editing, group decision-making, video conferencing, etc., at the same time and at different locations.

3. Asynchronous mode: A way of collaborating on the same task at the same place, at different times, such as rotating jobs.

4. Distributed asynchronous mode: a way to collaborate on the same tasks at different times and locations, such as e-mail, workflow, support for large-scale development projects, and more. Among them, the distributed synchronization mode is the main research and implementation object of CSCW system.

3. Similarities and differences of CSCW system and traditional distributed system

CSCW System is bound to be a distributed system, which has the following natural relations with the Distributed system. First, a fully autonomous distribution system, supporting the asynchronous or synchronous transmission of information between people, can partially complete support for cooperation between people. Second, the resource sharing system, which allows users of different computers to share the same system resources, is the necessary technology in CSCW system.

Therefore, the distributed processing technology is the basic supporting technology of CSCW system. There are obvious differences between CSCW system and distributed system. First, the distributed system pursues transparency, that is, to make users feel exclusive system when using the system, while the CSCW system pursues the opacity, that is, the system should let all users perceive each other to the operation of the shared object. Second, the distributed system mainly studies how to make each part of the system give full play to their respective performance,

In order to achieve the efficiency of the whole system, CSCW system, in addition to the pursuit of high performance, pay more attention to how to support efficient collaboration between collaborators.

4. Structure of CSCW system

1. The organization structure of CSCW system

The system structure of CSCW should be of great flexibility and easy to be expanded in the first place. Secondly, the whole CSCW system should have high running efficiency, and the ability of distributed parallel processing should be played as much as possible. At present, the realization ofCSCW system structure mainly includes: centralized, decentralized and mixed.

1. Centralized structure

A centralized structure is actually a client / server (client/server) structure. The server is responsible for the management, control and scheduling of the whole system, as well as all the application-related logic, data and so on, the client only has the application tool and the user interface module. All tasks that the user wants to perform are made to the server and completed by the server. The advantages of this structure are simple, shared information centralized storage, shared Operation Unified processing, consistency is easy to maintain, can easily realize the user's dynamic join and leave. But this kind of structure is more difficult to realize view-level and object-level sharing, the autonomy of the collaboration interface is very small, the user cannot directly control the implementation of the interface. In addition, the structure is a star-type cooperative network, the server is the core of the whole system, the system has a single point of reliance on the server, making it easy to become the bottleneck of the whole system.

2. Decentralized structure

A decentralized structure can also be called a repeating structure in which each node is in the same position, without a master or slave, also known as a peer entity pattern. Because there is no server, the system-related control and management modules are scattered across the client. The client manages itself, decides at what time, under what conditions to be activated, and what action to perform after activation, no client can directly activate and manipulate another client, but can only notify other client programs by modifying data or broadcasting signals. Since there is an identical collaboration interface handler on each node, the autonomy of the interface is easy to implement and interface coupling can be easily implemented in view-level and object-level sharing, and the method is robust, flexible, open and versatile, and it is easy to connect heterogeneous machines and software. However, because of the distribution of data storage and operation of the respective processing, so the global consistency is difficult to maintain, the real-time synchronization between nodes and the dynamic registration of users is also difficult to achieve.

3. Mixed-type construction

Hybrid structure combines the advantages of the first two structures, the server realizes the consistency of data information maintenance, user management and information forwarding and distribution functions, by the client to realize the interaction with the user, to achieve the application of specific applications related to the logic and other things can be done on the client, such as permission checks. This structure takes full advantage of the client computer resources, greatly reduces the working pressure of the server, reduces the bottleneck effect of the server, which can make the system have good flexibility, robustness and short response time, and ensure the consistency of the system information.

2. The architecture of CSCW system

The architecture of a CSCW system can be divided into three levels:

2. Basic distribution Functional layer: mainly includes the basic service of the network operating system and the general Distributed system technology, makes the multi-user and the distribution possible, provides the programming interface with the basic distribution function, completes the data transmission, the information accesses and other accesses the system resources function.

4. CSCW support platform: it is based on the collaboration agent and distributed object technology, and it satisfies the distribution object to cscw by extending the distribution service above the basic service functional layer The lack of support, and by invoking the basic distribution function to provide an implicit control strategy, support multimedia-oriented group communication, manage user group collaboration information, coordinate the collaboration between users, maintain the state of the whole system and provide access control mechanism for collaborative application and user-oriented programming interface. It can be subdivided into the distribution service support layer, the Information service support layer, and the collaboration support layer three layer. Distributed service support layer is to utilize and extend distribute object technology on the basic distribution function layer to strengthen distributed system support for CSCW in distribution, opening and group interaction, etc. the Information service support layer is the use of component technology to build a scalable component groupware , in order to improve the development efficiency and quality of CSCW application System; The collaboration support layer is the use of distributed agent technology to build collaborative agents-based collaboration strategies to meet Span lang= "en-US" >CSCW system requirements for dynamic collaboration.

6. Collaborative application layer: by invoking the services provided by the CSCW support platform, the user is supported to complete specific collaborative tasks and provide explicit control strategies to the users. Using the programming interface provided by CSCW support platform to develop a variety of collaborative applications, each collaborative application to deal with a collaborative task, the relationship between the collaborative application can be based on user requirements, and by the support Platform Unified Management. To support service access operations between levels, you define the operation primitives for Request,Response,indication, andResult four types. request, a service operation is requested by a service provider on the lower level of the service requester of the upper layer, and a service request response from the service provider to the service requester can be either a positive or a negative answer,Response; Indication, when a service requester receives a positive response from a service provider, it further issues a specific service instruction to the service provider; The result service provider receives the service instruction, executes the service operation, and returns the service operation result to the service requester.

5. CSCW Applications

2. Military applications: Various types of c3i systems at various levels of staff meeting systems. They can be either a remote conferencing system or a local conferencing system or a conference room system. Its size can be large and small. An emergency management information system developed by the U.S. Emergency Strategy Office OEP Emisariis a computer-supported remote conferencing system.

4. Distance Education: Collaborative learning under the network environment can enable students, teachers and experts to obtain rich resources from the Internet, while distance education and collaborative learning are basic and important ways and environments for people to work and study in the future.

6. The new development of office Automation (OA) and Management Information System (MIS) : traditional OA and mis can only manage and process data and text information. If it is combined with multimedia technology to increase the processing of information such as graphics, images, animations, video and sound, and with the support of communication network environment, it can greatly expand the functions and applications of OA and MIS system. The research and development of CS CW system for OA and MIS will make "intelligent building" become a reality.

8. Medical application: The research and development of CSCW system for medical treatment will make the computerized consultation, especially the remote expert consult, have more attractive: The critical patient can be rescued in time, and the patients in remote areas can get the same medical conditions as the city. Of course, no country's information infrastructure or information superhighway support can really achieve telemedicine. But at present, it is possible and realistic to research and develop the remote expert consultation system between the big hospitals at least in big cities.

Reference documents

[1] Smilin . CSCW: Computer-supported collaborative work . Journal of Communications,1995 year 1 , vol. 1 .

[2] Huang Yongzhan,CSCW system structure Analysis design . Journal of the Huanghe University of Science and Technology, vol. 5 , Part one .

[3] li people thick, Zheng Qinghua, Baojia . The concept, structure, theory and application of C-SCW [J]. Computer Engineering and Applications,1999 (2): 29-33.

[4] Smilin, to Yong, Yeung Kwong letter . Computer-supported collaborative work theory and application [M]. BEIJING : electronic Industry Press,2000:12.

[5] Jian, Zhou Mingquan, Shang . Research and implementation of CSCW model under heterogeneous environment [J]. Computer Science,2002 (): 104-106.

[6] Sun Yanchun, Liu Jiren . Research on architecture model of CSCW system [J]. Small microcomputer System,2001 (2): 210-213.

The understanding of Distributed system