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Introduction

A service oriented architecture in computer software design is an architectural pattern where in services are provided to the other components by

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.^[2]

Four features of a service according to open groups definition of a service is:

1. It logically represents a business activity with a specified outcome
2. It is self-contained
3. It is a black box for its consumers
4. It may consist of other underlying services^[3]

Different services can be used in conjunction to provide the functionality of a large

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:

1. Metadata must be provided such that software system can dynamically configure by discovery and incorporation of defined services. It must also maintain integrity
2. The metadata should be provided such that the system designer can understand and manage without any large amount of cost and effort put into it.

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.^[5]

A Manifesto was published for Service Oriented Architecture in October, 2009. This Manifesto came up with 6 core values which are listed as follows^[6]

1. Business value is given more importance than technical strategy 
2. Strategic goals is given more importance than project-specific benefits 
3. Intrinsic inter-operability is given more importance than custom integration 
4. Shared services is given more importance than specific-purpose implementations 
5. Flexibility is given more importance than optimization 
6. Evolutionary refinement is given more importance than pursuit of initial perfection

Framework

Solutions based on Service Oriented Architecture is viewed as six horizontal layers:^[7]

1. Consumer Interface Layer – It consists of the
   API
   for end users, applications or services.
2. Integration Layer – It invokes business process in the underlying layer that may be dependent on one or more services
3. Business Process
    Layer – It invokes the services lying in the service layer.
4. Service Layer – It consolidates various service components in the service component layer and invokes them at once.
5. Service Components – These are components which are used to build a service. It invokes solution components within the operational systems layer .
6. Operational Systems – It is the lowest lying layer and provides what is requested by the consumers.

Principles

Service Oriented Architecture does not have any industry established standards. However, many principles have been published by different Institutions. Some of these^[8][9][10] include the following:

• Standardized service contract: Services adhere to a standard communications agreements, as defined collectively by one or more service-description documents within a given set of services.
• Service loose coupling: The relationship between services is minimized to the level that they are only aware of their existence.
• Service abstraction: The services act as black boxes, that is their inner logic is hidden from the consumers
• Service re usability: Logic is divided into various services, to promote re use of code.
• Service autonomy: Services are independent and control the functionality they encapsulate, from a Design-time and a run-time perspective.
• Service statelessness: Services are stateless that is either return the requested value or a give an exception hence minimizing resource use^[11].
• Service discoverability: Services are supplemented with communicative meta data by which they can be effectively discovered and interpreted.
• Service composability: Services can be used to compose other services.
• Service granularity: A principle to ensure services do granular, that is atomic functions.
• Service optimization:High quality services are preferred to low quality ones..
• Service location transparency: Services can be called from anywhere within the network that it is located no matter where it is present.

Service Oriented Architecture Implementation Framework

See also:

The collection of all tools and run time infrastructure software required to implement Service Oriented Architecture is known as

Web services approach

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^[12].

Each SOA building block can play any of the three roles:

1. Service provider: It creates a web service and provides its information to the service registry. Each provider debates upon a lot of hows and whys likes which service to expose, whom to give more importance: security or easy availability, what price to offer the service for and many more. The provider also has to decide what category the service should be listed in for a given broker service and what sort of trading partner agreements are required to use the service.
2. Service broker: Is is also known as the service registry. Its main functionality is to make the information regarding the web service available to any potential requester. Whoever implements the broker decides the scope of the broker. Public brokers are available anywhere and everywhere but private brokers are only available to a limited amount of public.
3. Service requester/consumer: It locates entries in the broker registry using various find operations and then binds to the service provider in order to invoke one of its web services. Whichever service the service-consumers need, they have to take it into the brokers, bind it with respective service and then use it. They can access multiple services if the service provides multiple services.

Web service protocols

See also: List of web service protocols

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

Other SOA concepts

Architectures can operate independently of specific technologies and can therefore be implemented using a wide range of technologies, including:

• SOAP, RPC
• REST
• DCOM
• CORBA
• OPC-UA
• Web services
• DDS
• Java RMI
• WCF (Microsoft's implementation of web services now forms a part of WCF)
• Apache Thrift
• SORCER

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 

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 

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 aproject 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.

Challenges

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.^[16]

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:^[17]

• heterogeneity and complexity of solution
• huge set of testing combinations due to integration of autonomous services
• Inclusion of services from different and competing vendors
• platform is continuously changing due to availability of new features and services.

Videos

What is SOA?(Youtube)

References

Category:Architectural pattern (computer science) Category:Enterprise application integration Category:Service-oriented (business computing) Category:Web services Category:Software design patterns