SOA Tutorial

SOA stands for service oriented architecture. From OOA to SOA, computing and development approach of software services are changing rapidly.

SOA are based on a mesh of software services. Services comprise unassociated, loosely coupled units of functionality that have no calls to each other embedded in them. Each service implements one action, such as filling out an online application for an account, viewing an online bank-statement, or placing an online booking or airline ticket order. Instead of services embedding calls to each other in their source code they use defined protocols that describe how services pass and parse messages, using description meta-data.

The developer associates individual SOA objects by using orchestration. In the process of orchestration the developer associates software functionality (the services) in a non-hierarchical arrangement (in contrast to a class hierarchy) using a software tool that contains a complete list of all available services, their characteristics, and the means to build an application utilizing these sources.

Underlying and enabling all of this requires meta data in sufficient detail to describe not only the characteristics of these services, but also the data that drives them. Programmers have made extensive use of XML in SOA to structure data that they wrap in a nearly exhaustive description-container. Analogously, WSDL typically describe the services themselves, while SOAP describes the communications protocols. Whether these description languages are the best possible for the job, and whether they will remain the favorites in the future, remains an open question. In the meantime SOA depends on data and services that are described metadata that should meet the following two criteria:

  • the metadata should come in a form that software systems can use to configure dynamically by discovery and incorporation of defined services, and also to maintain coherence and integrity
  • the metadata should come in a form that system designers can understand and manage with a reasonable expenditure of cost and effort

Service Oriented Architecture or SOA for short is a new architecture for the development of loosely coupled distributed applications. In fact service-oriented architecture is collection of many services in the network. These services communicate with each other and the communications involves data exchange & even service coordination. Earlier SOA was based on the DCOM or Object Request Brokers (ORBs). Nowadays SOA is based on the Web Services.Broadly SOA can be classified into two terms: Services and Connections

Services:

A service is a function or some processing logic or business processing that is well-defined, self-contained, and does not depend on the context or state of other services. Example of Services are Loan Processing Services, which can be self-contained unit for process the Loan Applications. Other example may be Weather Services, which can be used to get the weather information. Any application on the network can use the service of the Weather Service to get the weather information.

Connections:

Connections means the link connecting these self-contained distributed services with each other, it enable client to Services communications. In case of Web services SOAP over HTTP is used to communicate the between services.

The following figure is a typical example of the service-oriented architecture. It shows how a service consumer sends a service request to a service provider. After accepting the request, service provider send a message to the service consumer. In this case a service provider can also be a service consumer.Connections means the link connecting these self-contained distributed services with each other, it enable client to Services communications. In case of Web services SOAP over HTTP is used to communicate the between services

The following figure is a typical example of the service-oriented architecture. It shows how a service consumer sends a service request to a service provider. After accepting the request, service provider send a message to the service consumer. In this case a service provider can also be a service consumer.

Different Technologies Used:

SOA is much different from point-to-point architectures. SOA comprise loosely coupled, highly interoperable application services. These services can be developed in different development technologies (such as Java, .NET, C++, PERL, PHP), the software components become very reusable i.e. the same C# (C Sharp) service may be used by a Java application and / or any other programming language. WSDL defines an standard, which encapsulates / hides the vendor / language specific implementation from the calling client / service

SOA definitions (Fromhttp://en.wikipedia.org/wiki/Service-oriented_architecture)

Term Definition / Comment
service (Ideally) a self-contained, stateless business function which accepts one or more requests and returns one or more responses through a well-defined, standard interface. Services can also perform discrete units of work such as editing and processing a transaction. Services should not depend on the state of other functions or processes. The technology used to provide the service, such as a programming language, does not form part of this definition.
orchestration Sequencing services and providing additional logic to process data. Does not include data presentation.
stateless Not depending on any pre-existing condition. In a SOA, services should not depend on the condition of any other service. They receive all information needed to provide a response from the request. Given the statelessness of services, service consumers can sequence (orchestrate) them into numerous flows (sometimes referred to as pipelines) to perform application logic.
provider The function which performs a service in response to a request from a consumer.
consumer The function which consumes the result of a service supplied by a provider.
discovery Service oriented architecture relies on the ability to identify services and their capabilities. Therefore, a SOA depends on a directory which describes the services available in its domain.
binding The relationship between a service provider and consumer is dynamic; it is established at runtime by a binding mechanism.

Why SOA?

SOA architecture enables seamless Enterprise Information Integration. Here are some of the Benefits of the Service Oriented Architecture:

Due to its platform independence, it allows companies to use the software and hardware of their choice .
There is no threat of vendor lock-in
SOA enables incremental development, deployment, and maintenance.
Companies can use the existing software (investments) and use SOA to build applications without replacing existing applications
The training costs are low, so the available labor pool can be used for running the applications