|Deployment||In a shared Bus||At the edge|
|Goals||One for all||As per the business units|
|Back-end implementation||Not prescriptive||prescriptive|
SOA is an architecture for building applications using reusable, interoperable services which have well defined business functionalities and can be orchestrated to achieve a specific functionality by utilizing them together.
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SOA principles were first defined by Thomas Erl. These 8 principles are underlying to any good architecture that utilizes SOA design to build their products and services:
Transforming an enterprise business to Service Oriented Architecture includes obtaining standardized service contract, service reusability, service abstraction, service loose coupling, service compos ability and so on.
Of course SOA is an architectural model agnostic to technology platforms and every enterprise can pursue the strategic goals associated with service-oriented computing using different technologies. However in the current marketplace, Web Services are probably the technology platform that better suits SOA principles and are most used to get to this architecture.
It is an autonomous, reusable, discoverable, stateless functionality that has the necessary granularity, and can be part of a composite application or a composite service.A reusable service should be identified with a business activity described by the service specifications (design-time contract).
A service’s constraints, including security, QoS, SLA, usage policies, may be defined by multiple run-time contracts, multiple interfaces (the WSDL for a SOAP Web Service), and multiple implementations (the code).
A reusable service should be governed at the enterprise level throughout its entire lifecycle, from design-time through run-time. Its reuse should be promoted through a prescriptive process, and that reuse should be measured.
SOA is an architectural style. And building architecture is a Top-Down process and not Bottom-Up. The most compelling reason for saying that Web Services are not SOA is that they are technical stuff, often built with a Bottom-Up approach. Building a Bottom-UP SOA is a wrong approach and might lead to an architecture with a lot of redundancy or maybe no architecture at all.
However, the result of building SOA only Top-Down could be perceptual Architecture building with no run time artifacts, so some SOA efforts should be Bottom-Up efforts. To sum up: Initially SOA is a Top-Down approach but pragmatic approach requires mixing Top-Down approach with Bottom-Up approach.
One strategy for achieving loose coupling is to use the service interface (the WSDL for a SOAP Web Service) to limit this dependency, hiding the service implementation from the consumer. Loose coupling can be addressed by encapsulating the service functionalities in a manner that limits the impact of changes to the implementation on the service interface.
However, at some point you will need to change the interface and manage versioning without impacting service consumers, in addition to managing multiple security constraints, multiple transports, and other considerations.
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One of the most common pitfalls is to view SOA as an end, rather than a means to an end. Developers who focus on building an SOA solution rather than solving a specific business problem are more likely to create complex, unmanageable, and unnecessary interconnections between IT resources.
Another common pitfall is to try to solve multiple problems at once, rather than solving small pieces of the problem. Taking a top-down approach—starting with major organization-wide infrastructure investments—often fails either to show results in a relevant timeframe or to offer a compelling return on investment.
Surely cultural. SOA does require people to think of business and technology differently. Instead of thinking of technology first (e.g., If we implement this system, what kinds of things can we do with it?), practitioners must first think in terms of business functions, or services (e.g., My company does these business functions, so how can I set up my IT system to do those things for me most efficiently?).
It is expected that adoption of SOA will change business IT departments, creating service-oriented (instead of technology-oriented) IT organizations.