Distributed System Characteristics

Common Characteristics

Certain common characteristics can be used to assess distributed systems

  • Resource Sharing
    • Openness
    • Concurrency
    • Scalability
    • Fault Tolerance
    • Transparency

Resource Sharing

  • Ability to use any hardware, software or data anywhere in the system.
  • Resource manager controls access, provides naming scheme and controls concurrency.
  • Resource sharing model (e.g. client/server or object-based) describing how
  • resources are provided,
    • they are used and
    • provider and user interact with each other.

Openness

  • Openness 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.

Concurrency

Components 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 updates
      • Inconsistent analysis

Scalability

  • Adaption of distributed systems to
  • accomodate more users
  • respond faster (this is the hard one)
    • Usually done by adding more and/or faster processors.
    • Components should not need to be changed when scale of a system increases.
    • Design components to be scalable

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
  • recovery
  • redundancy

Transparency

Distributed systems should be perceived by users and application programmers as a whole rather than as a collection of cooperating components.

  • Transparency has different dimensions that were identified by ANSA.
  • These represent various properties that distributed systems should have.
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