SYSTEM MODELS




 

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commonly used forms network interconnections. Client-server and peer-to-peer are two of the most elements being individual computers or aggregates of them supported by appropriate communication tasks performed by its computational elements; the computational Architectural models describe a system in terms of the computational and and their interconnectivity, without details of specific technologies.
Physical models consider the types of computers and devices that constitute a system which the design of distributed systems can usefully be described and discussed:
This chapter provides an explanation of three important and complementary ways in
ofarchitectural model for distributed systems.
Fundamental models take an abstract perspective in order to describe solutions to individual issues faced by most distributed systems.
There is no global time in a distributed system, so the clocks on different computers do not necessarily give the same time as one another. All communication between processes is achieved by means of messages. Message communication over a computer network
can be affected by delays, can suffer from a variety of failures and is vulnerable to security attacks. These issues are addressed by three models:
• The interaction model deals with performance and with the difficulty of setting time limits in a distributed system, for example for message delivery.
• The failure model attempts to give a precise specification of the faults that can be exhibited by processes and communication channels. It defines reliable communication and correct processes.
• The security model discusses the possible threats to processes and communication channels. It introduces the concept of a secure channel, which is secure against those threats.

 

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Frequently Asked Questions

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Ans: Resource sharing is the main motivating factor for constructing distributed systems. Resources such as printers, files, web pages or database records are managed by servers of the appropriate type. For example, web servers manage web pages and other web resources. Resources are accessed by clients – for example, the clients of web servers are generally called browsers. view more..
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Ans: The Web began life at the European centre for nuclear research (CERN), Switzerland, in 1989 as a vehicle for exchanging documents between a community of physicists connected by the Internet [Berners-Lee 1999]. A key feature of the Web is that it provides a hypertext structure among the documents that it stores, reflecting the users’ requirement to organize their knowledge. view more..
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Ans: Reliability and security issues are critical in the design of most computer systems. The performance aspect of quality of service was originally defined in terms of responsiveness and computational throughput, but it has been redefined in terms of ability to meet timeliness guarantees, as discussed in the following paragraphs view more..
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Ans: Physical models consider the types of computers and devices that constitute a system and their interconnectivity, without details of specific technologies. view more..
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Ans: The discussion and examples of Chapter 1 suggest that distributed systems of different types share important underlying properties and give rise to common design problems. In this chapter we show how the properties and design issues of distributed systems can be captured and discussed through the use of descriptive models view more..
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Ans: A physical model is a representation of the underlying hardware elements of a distributed system that abstracts away from specific details of the computer and networking technologies employed. view more..
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Ans: Major concerns are to make the system reliable, manageable, adaptable and cost-effective. The architectural design of a building has similar aspects – it determines not only its appearance but also its general structure and architectural style (gothic, neo-classical, modern) and provides a consistent frame of reference for the design view more..
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Ans: From a system perspective, the answer is normally very clear in that the entities that communicate in a distributed system are typically processes, leading to the prevailing view of a distributed system as processes coupled with appropriate interprocess communication paradigms view more..
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Ans: ion for a given problem domain. This is a large topic, and many architectural patterns have been identified for distributed systems. In this section, we present several key architectural patterns in distributed systems, including layering and tiered architectures and the related concept of thin clients (including the specific mechanism of virtual network computing). We also examine web services as an architectural pattern and give pointers to others that may be applicable in distributed systems. view more..
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Ans: As mentioned in the introduction, networks are everywhere and underpin many everyday services that we now take for granted: the Internet and the associated World Wide Web, web search, online gaming, email, social networks, eCommerce, etc. To illustrate this point further, consider Figure 1.1 , which describes a selected range of key commercial or social application sectors highlighting some of the associated established or emerging uses of distributed systems technology. view more..
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Ans: If another organization develops or runs a computer application for your organization, that practice is called outsourcing. Outsourcing includes a spectrum of working arrangements view more..
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Ans: We can group organizations that produce software into six major categories. view more..
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Ans: Once you have decided to purchase off-the-shelf software rather than write some or all of the software for your new system, how do you decide what to buy? Several criteria need consideration, and special ones may arise with each potential software purchase. view more..
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Ans: Reuse is the use of previously written software resources in new applications. Because so many bits and pieces of applications are relatively generic across applications, it seems intuitive that great savings can be achieved in many areas if those generic bits and pieces do not have to be written anew each time they are needed. view more..
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Ans: Pine Valley Furniture (PVF) Company manufactures high-quality wood furniture and distributes it to retail stores within the United States. Its product lines include dinette sets, stereo cabinets, wall units, living room furniture, and bedroom furniture. view more..
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Ans: During project initiation the project manager performs several activities that assess the size, scope, and complexity of the project, and establishes procedures to support subsequent activities. view more..
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Ans: The next step in the project management process is project planning. Project planning involves defining clear, discrete activities and the work needed to complete each activity within a single project. view more..
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Ans: Project execution puts the baseline project plan into action. view more..



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