Presented by: Nazim AliEn no:GH7764

Faculty no:13BCA141

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Distributed Information System

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Outline

1. What is a Distributed System2. Centralized Vs Distributed Systems3. Common Characteristics4. Basic Design Issues5. Examples of Distributed Systems6. Advantages and Disadvantages 7. Conclusion8. References

What is a Distributed System?

Definition: A distributed system is one in which components located at networked computers communicate and coordinate their actions only by passing messages. This definition leads to the following characteristics of distributed systems.

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Distributed System CharacteristicsMultiple autonomous componentsComponents are not shared by all usersResources may not be accessibleSoftware runs in concurrent processes on

different processorsMultiple points of controlMultiple points of failure

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Centralized Vs Distributed SystemsCentralized:

Collecting all information at one place allows better decision to be made but is less robust and can put a heavy load on central machine.

Distributed: Opposite to Centralized (may also be

termed as Decentralized). Here there is no central machine and algorithm is implemented on all the machine.

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Common CharacteristicsWhat are we trying to achieve when we construct a

distributed system?Certain common characteristics can be used to

assess distributed systemsHeterogeneityOpennessSecurityFailure HandlingConcurrency

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HeterogeneityVariety and differences in

NetworksComputer hardwareOperating systemsProgramming languages Implementations by different developers

Middleware as software layers to provide a programming abstraction as well as masking the heterogeneity of the underlying networks, hardware, OS, and programming languages (e.g., CORBA).

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OpennessOpenness is concerned with extensions

and improvements of distributed systems.

Detailed interfaces of components need to be published.

New components have to be integrated with existing components.

Differences in data representation of interface types on different processors (of different vendors) have to be resolved.

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SecurityIn a distributed system, clients send

requests to access data managed by servers, resources in the networks: Doctors requesting records from hospitals Users purchase products through electronic

commerce\

Security is required for: Concealing the contents of messages: security and

privacy Identifying a remote user or other agent correctly

(authentication)

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Failure Handling (Fault Tolerance)

Hardware, software and networks fail!Distributed systems must maintain

availability even at low levels of hardware/software/network reliability.

Fault tolerance is achieved by recoveryredundancy

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ConcurrencyComponents in distributed systems are

executed in concurrent processes.Components access and update shared

resources (e.g. variables, databases, device drivers).

Integrity of the system may be violated if concurrent updates are not coordinated.Lost updatesInconsistent analysis

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Basic Design IssuesGeneral software engineering

principles include rigor and formality, separation of concerns, modularity, abstraction, anticipation of change, …

Specific issues for distributed systems:NamingCommunicationSystem architecture

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NamingA name is resolved when translated into an

interpretable form for resource/object reference.Communication identifier (IP address + port

number)Name resolution involves several translation

stepsDesign considerations

Choice of name space for each resource typeName service to resolve resource names to

comm. id.Name services include naming context

resolution, hierarchical structure, resource protection

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CommunicationSeparated components communicate with

sending processes and receiving processes for data transfer and synchronization.

Message passing: send and receive primitivessynchronous or blockingasynchronous or non-blockingAbstractions defined: channels, sockets, ports.

Communication patterns: client-server communication (e.g., RPC, function shipping) and group multicast

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System ArchitectureClient-ServerPeer-to-PeerServices provided by multiple serversProxy servers and cachesMobile code and mobile agentsNetwork computersThin clients and mobile devices

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Examples of Distributed SystemsLocal Area Network and IntranetDatabase Management SystemAutomatic Teller Machine NetworkInternet

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EconomicSpeed Inherent distribution of applicationsReliabilityExtensibility and Incremental GrowthData integration

Advantages of Distributed system

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Disadvantages of Distributed system

ComplexityNetwork problemSecurity

ConclusionDespite the increased complexity and the difficulty of building distributed computing systems, the installation and the use of distributed computing systems are rapidly increasing. This is mainly because the advantages of distributed computing systems overcome their disadvantages.

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Referenceswww.Wikipedia.comwww.slideshare.com“Advanced Concepts in Operating Systems”

by Mukesh Singhal and Niranjan Shivaratri“Distributed Algorithms” by Nancy Lynchwww.authorstream.comwww.google.com

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