||This article contains weasel words: vague phrasing that often accompanies biased or unverifiable information. (February 2015)|
A service oriented architecture in computer software design is an architectural pattern where in services are provided to the other components by application components, through a communication protocol over a network. The basic fundamental principles of service oriented architecture is independent of vendors, products and technologies.
The usage of the term service is usually surrounded by a lot of ambiguity, However, in the general sense, the word service refers to discrete unit of functionality that can be acted upon independently such as an act of retrieving a credit card statement, online. In context of service oriented architecture, service refers to Web Services, which are responsible for communication between electronic devices to communicate over the World Wide Web. Web Services generally provide object-oriented web based interface to database servers which are used by mobile applications, web servers or web application.
Four features of a service according to open groups definition of a service is:
Different services can be used in conjunction to provide the functionality of a large software application. Service oriented architecture makes it easier for software components to communicate and cooperate over the network, without requiring any human interaction or changes in the underlying program. so that service candidates can be redesigned before their implementation.
In Service Oriented Architecture, services use protocols which describe how they pass and parse messages using description metadata, this metadata describes both the characteristics of the service and the data that drives it. The Web Services Description Language (WSDL) describes services themselves, however SOAP (Simple Object Access Protocol) describes the communications protocols used in the process of communication. SOA depends on data and services described by metadata. It should meet the following two criteria:
Service Oriented Architecture aims to allow users to combine large chunks of functionality to form applications which are built purely from existing services and combining them in an ad hoc manner. Service Orientation Architecture by its very nature relies on service orientation as a major principle for design. Service presents a simple interface to the requester that abstracts away the underlying complexity acting as a black box, Further users can also access these independent services without any knowledge of their internal implementation.
A Manifesto was published for Service Oriented Architecture in October, 2009. This Manifesto came up with 6 core values which are listed as follows
Various horizontal layers which constitute the Service Oriented Architecture framework are listed below:
Service-orientation requires loose coupling of services with operating systems and other technologies that underlie applications. SOA separates functions into distinct units, or services, which developers make accessible over a network in order to allow users to combine and reuse them in the production of applications. These services and their corresponding consumers communicate with each other by passing data in a well-defined, shared format, or by coordinating an activity between two or more services.
SOA can be seen as part of the continuum which ranges from the older concept of distributed computing and modular programming, through SOA, and on to current practices of mashups, SaaS, and cloud computing (which some see as the offspring of SOA).
There are no industry standards relating to the exact composition of a service-oriented architecture, although many industry sources have published their own principles. Some of these include the following:
Service Oriented Architecture is implemented in Web services. This is done to make the functional building-blocks accessible over standard Internet protocols that are independent of platforms and programming languages. These services can represent either new applications or just wrappers around existing legacy systems to make them network-enabled.
Each SOA building block can play any of the three roles:
Implementers commonly build SOAs using web services standards (for example, SOAP) that have gained broad industry acceptance after recommendation of Version 1.2 from the W3C (World Wide Web Consortium) in 2003. These standards (also referred to as web service specifications) also provide greater interoperability and some protection from lock-in to proprietary vendor software. One can, however, implement SOA using any service-based technology, such as Jini, CORBA or REST.
Architectures can operate independently of specific technologies and can therefore be implemented using a wide range of technologies, including:
Implementations can use one or more of these protocols and, for example, might use a file-system mechanism to communicate data following a defined interface specification between processes conforming to the SOA concept. The key is independent services with defined interfaces that can be called to perform their tasks in a standard way, without a service having foreknowledge of the calling application, and without the application having or needing knowledge of how the service actually performs its tasks. SOA enables the development of applications that are built by combining loosely coupled and interoperable services.
These services inter-operate based on a formal definition (or contract, e.g., WSDL) that is independent of the underlying platform and programming language. The interface definition hides the implementation of the language-specific service. SOA-based systems can therefore function independently of development technologies and platforms (such as Java, .NET, etc.). Services written in C# running on .NET platforms and services written in Java running on Java EE platforms, for example, can both be consumed by a common composite application (or client). Applications running on either platform can also consume services running on the other as web services that facilitate reuse. Managed environments can also wrap COBOL legacy systems and present them as software services..
High-level languages such as BPEL and specifications such as WS-CDL and WS-Coordination extend the service concept by providing a method of defining and supporting orchestration of fine-grained services into more coarse-grained business services, which architects can in turn incorporate into workflows and business processes implemented in composite applications or portals
Service-oriented modeling is an SOA framework that identifies the various disciplines that guide SOA practitioners to conceptualize, analyze, design, and architect their service-oriented assets. The Service-oriented modeling framework (SOMF) offers a modeling language and a work structure or "map" depicting the various components that contribute to a successful service-oriented modeling approach. It illustrates the major elements that identify the "what to do" aspects of a service development scheme. The model enables practitioners to craft a project plan and to identify the milestones of a service-oriented initiative. SOMF also provides a common modeling notation to address alignment between business and IT organizations.
Some enterprise architects believe that SOA can help businesses respond more quickly and more cost-effectively to changing market conditions. This style of architecture promotes reuse at the macro (service) level rather than micro (classes) level. It can also simplify interconnection to—and usage of—existing IT (legacy) assets.
With SOA, the idea is that an organization can look at a problem holistically. A business has more overall control. Theoretically there would not be a mass of developers using whatever tool sets might please them. But rather they would be coding to a standard that is set within the business. They can also develop enterprise-wide SOA that encapsulates a business-oriented infrastructure. SOA has also been illustrated as a highway system providing efficiency for car drivers. The point being that if everyone had a car, but there was no highway anywhere, things would be limited and disorganized, in any attempt to get anywhere quickly or efficiently. IBM Vice President of Web Services Michael Liebow says that SOA "builds highways".
In some respects, SOA could be regarded as an architectural evolution rather than as a revolution. It captures many of the best practices of previous software architectures. In communications systems, for example, little development of solutions that use truly static bindings to talk to other equipment in the network has taken place. By formally embracing a SOA approach, such systems can position themselves to stress the importance of well-defined, highly inter-operable interfaces.
A service comprises a stand-alone unit of functionality available only via a formally defined interface. Services can be some kind of "nano-enterprises" that are easy to produce and improve. Also services can be "mega-corporations" constructed as the coordinated work of subordinate services.
A mature roll out of SOA effectively defines the API of an organization.
Reasons for treating the implementation of services as separate projects from larger projects include:
An indirect benefit of SOA involves dramatically simplified testing. Services are autonomous, stateless, with fully documented interfaces, and separate from the cross-cutting concerns of the implementation.
If an organization possesses appropriately defined test data, then a corresponding stub is built that reacts to the test data when a service is being built. A full set of regression tests, scripts, data, and responses is also captured for the service. The service can be tested as a 'black box' using existing stubs corresponding to the services it calls. Test environments can be constructed where the primitive and out-of-scope services are stubs, while the remainder of the mesh is test deployments of full services. As each interface is fully documented with its own full set of regression test documentation, it becomes simple to identify problems in test services. Testing evolves to merely validate that the test service operates according to its documentation, and finds gaps in documentation and test cases of all services within the environment. Managing the data state of idempotent services is the only complexity.
Examples may prove useful to aid in documenting a service to the level where it becomes useful. The documentation of some APIs within the Java Community Process provide good examples. As these are exhaustive, staff would typically use only important subsets. The 'ossjsa.pdf' file within JSR-89 exemplifies such a file.
A primary challenge faced by Service Oriented Architecture is managing of metadata. Environments based on Service Oriented Architecture include many services which communicate among each other to perform tasks. Due to the fact that the design may involve multiple services working in conjunction, an Application may generate millions of messages. Further services may belong to different organizations or even competing firms creating a huge trust issue. Thus SOA governance comes into the scheme of things.
Another major problem faced by SOA is the lack of a uniform testing framework. There are no tools that provide the required features for testing these services in a Service Oriented Architecture. The major causes of difficulty are:
Some criticisms of SOA depend on conflating SOA with Web services. In the absence of native or binary forms of remote procedure call (RPC), applications could run more slowly and require more processing power, increasing costs. Most implementations do incur these overheads, but SOA can be implemented using technologies (for example, Java Business Integration (JBI), Windows Communication Foundation (WCF) and data distribution service (DDS)) that do not depend on remote procedure calls or translation through XML. At the same time, emerging open-source XML parsing technologies (such as VTD-XML) and various XML-compatible binary formats promise to significantly improve SOA performance. Services implemented using JSON instead of XML do not suffer from this performance concern.
Stateful services require both the consumer and the provider to share the same consumer-specific context, which is either included in or referenced by messages exchanged between the provider and the consumer. This constraint has the drawback that it could reduce the overall scalability of the service provider if the service-provider needs to retain the shared context for each consumer. It also increases the coupling between a service provider and a consumer and makes switching service providers more difficult. Ultimately, some critics feel that SOA services are still too constrained by applications they represent.
Tim O'Reilly coined the term "Web 2.0" to describe a perceived, quickly growing set of web-based applications. A topic that has experienced extensive coverage involves the relationship between Web 2.0 and Service-Oriented Architectures (SOAs).
SOA is the philosophy of encapsulating application logic in services with a uniformly defined interface and making these publicly available via discovery mechanisms. The notion of complexity-hiding and reuse, but also the concept of loosely coupling services has inspired researchers to elaborate on similarities between the two philosophies, SOA and Web 2.0, and their respective applications. Some argue Web 2.0 and SOA have significantly different elements and thus can not be regarded "parallel philosophies", whereas others consider the two concepts as complementary and regard Web 2.0 as the global SOA.
The philosophies of Web 2.0 and SOA serve different user needs and thus expose differences with respect to the design and also the technologies used in real-world applications. However, as of 2008[update], use-cases demonstrated the potential of combining technologies and principles of both Web 2.0 and SOA.
Microservices are a modern interpretation of service-oriented architectures used to build distributed software systems. Services in a microservice architecture are processes that communicate with each other over the network in order to fulfill a goal. These services use technology agnostic protocols, which aid in encapsulating choice of language and frameworks, making their choice a concern internal to the service. Microservices architectural style is a first realisation of SOA that has happened after the introduction of DevOps and this is becoming the standard for building continuously deployed systems.
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