Tuesday, 10 August 2010

Notes on Service-Orientation

I was thumbing through my copy of SOA Principles of Service Design by Thomas Erl, and thought I’d make a few notes on some of the standout concepts as well as notes picked up from other locations.

As usual this is going to be a work in progress…

OASIS (Organization for the Advancement of Structured Information Standards) defines SOA as:

“A paradigm for organizing and utilizing distributed capabilities that may be under the control of different ownership domains. It provides a uniform means to offer, discover, interact with and use capabilities to produce desired effects consistent with measurable preconditions and expectations.”

Principles of Service-Orientation as a design paradigm

Erl describes some of the principles of a service-oriented design paradigm in the following terms:

  • Standardised Service Contract
    • The purpose and capabilities of a service are exposed by a service contract.
  • Service Loose Coupling
    • Emphasis should be placed on reducing dependencies between the service contract, its implementation and its consumers.
  • Service Abstraction
    • Hide the underlying details of a service from its consumers.
    • Enables and preserves loose coupling. 
  • Service Reusability
    • Emphasises the positioning of services as enterprise resources “with agnostic functional contexts”.
  • Service Autonomy
    • Underlying solution logic needs to have a significant degree of control over its environment and resources.
  • Service Statelessness
    • “The management of excessive state information can compromise the availability of a service and undermine its scalability and potential.”
    • Ideally, services should remain stateful only when required.
  • Service Discoverability
    • “For services to be positioned as IT assets with repeatable ROI they need to be easily identified and understood when opportunities present themselves.”
  • Service Composability
    • Services should be capable of participating as effective composition members.

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