Chapter 2 Distributed sysytem - Architectures 02:...

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Architectures
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02: Architectures 2.1 Architectural styles 2.2 System architectures 2.3 Architectures versus middleware 2.4 Self-management in distributed systems
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What is a Distributed System? A distributed system is: a collection of independent computers that appears to its users as a single coherent system
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Definition of a Distributed System (II) Independent  hardware installations Uniform software layer  (middleware)  Note : the middleware layer extends over multiple machines 1.1
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Architectural Style A architectural style is formulated in terms of components, the way that components are connected to each other, the data exchanged between components, and finally show these elements are jointly configured into a system. A component is a modular unit with well-defined required and provided interfaces that is replaceable within its environment. A connector is a mechanism that mediates communication, coordination, or cooperation among components. E.g., a connector can be formed by the facilities for remote procedure call, Message passing, or streaming data 2.1 Architectural styles
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Several Architecutre Styles Using components and connectors , we can come to various configurations, in turn have been classified into architectural styles. 1.Layered architectures 2.Object-based architectures 3.Data-centered architectures 4.Event-based architectures
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Architectural styles(1/4): Layered style Observation : Layered style is used for client-server system; An key observation is that control generally flows from layer to layer:  requests go  down the hierarchy where as the results flow upward. 2.1 Architectural styles
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Architectural styles (2/4): object based Basic idea : Organize into logically different components, and subsequently distribute those components over the various machines. Observation : object-based style for distributed object systems. In essence, each object corresponds to what we have defined as a component and these components are connected through a (remote) procedure call mechanism. 2.1 Architectural styles
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Architectural styles (3/4): data-centered Basic idea : Processes communicate through a common (passive or active) repository. As important as the layered and object- based architectures E.g., a wealth of networked applications have been developed that rely on a shared distributed file system in which virtually all communication takes place through files. Likewise, Web-based distributed systems 2.1 Architectural styles
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Architectural Styles (4/4): event-based Observation : Decoupling processes in space (“anonymous”) and also time (“asynchronous”) has led to alternative styles: (a) Publish/subscribe [decoupled in space ] and (b) Shared data spaces [decoupled in space and time ] 2.1 Architectural styles
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Outline 2.1 Architectural styles 2.2 System architectures 2.2.1 Centralized architectures
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Chapter 2 Distributed sysytem - Architectures 02:...

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