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Service-Oriented Architecture (SOA)

SOA is a software architecture in which reusable services are deployed into application

servers and then consumed by clients in different applications or business processes.

Service-oriented architecture (SOA) is an approach for loosely coupled, protocol

independent, standards-based distributed computing where software resources available

on the network are considered as Services. It's an architectural style of building software

applications that promotes loose coupling between components so that we can reuse

them.

It is a new way of building applications with the following characteristics: Services are software components that have published contracts/interfaces;

these contracts are platform, language, and operating-system-independent. XMLand the Simple Object Access Protocol (SOAP) are the enabling technologies forSOA, since they're platform-independent standards.

Consumers can dynamically discover services.

Services are interoperable.

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ServiceDirectory

ServiceService

Consumer

Invokes

Finds

Register

The basic building block of SOA is the service. A service is a self-contained softwaremodule that performs a predetermined task. Services are software components thatdon't require developers to use a specific underlying technology. SOA promotesapplication assembly because services can be reused by numerous consumers.Moreover, creating applications that leverage these different technologies hashistorically been a daunting task. SOA provides a clear solution to these application

integration issues by allowing systems to expose their functionality via standardized,interoperable interfaces. Using SOA offers several key advantages. One can Adapt applications to changing technologies. Easily integrate applications with other systems. Leverage existing investments in legacy applications. Quickly and easily create a business process from existing services.

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Different Layers for Service-Oriented Applications

Presentation LayerThis represents the client view of the application. JSPs to be used to represent the client

view of the application. JSPs form the view component of the MVC architecture. Client

can be presented different views of the same content. Every client request is secured

and sent to the application deployed on the J2EE complaint application server. Action

servlets of Struts framework acts as central controller for all such requests and forwards

the request to Session Facade layer.

Session Facade Layer

Session facade layer helps in reducing Traffic over the net. This layer provides all middle

ware services like Transaction, security and resource pooling. This layer forwards the

request to business layer .EJB component is used to represent this layer.

Business Layer

Every business rule is written in this layer. Business rule is selected based on the

incoming request and data required to process the request is fetched using data layer.

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Application Services InfrastructureServices

Session Facade Layer

Business Layer

Data Layer

Data captureServices

Search Services

Reporting

Services

Presentation Layer

Security

Logging

Service Locator

Error HandlingWorkflowservices

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Data Layer

Logic to access data is embedded in this layer. This layer is represented by Data Access

Objects (DAO). DAO fetches or saves or deletes data in DB2 database using

appropriate drivers.

Application Services

Proposed application architecture incorporates all application related services like data

capture, search, work flow and reporting.

Infrastructure services

Architecture incorporates all essential infrastructure services like security, logging, error

handling and service locator. Stakeholders need to access the application using proper

authorization and authentication. One-way encryption is used to store passwords.

Log4J/Server logs are configured for all logging requirements. All system level and

application level errors are handled. Service locator provides the service of locating

resources like EJB and data source.

Features of SOA

Technology Independence: The Consumer of a Service component iscompletely independent of the technology of the Provider component and vice-versa.

Life-cycle Independence: Each of the Provider and Consumer Servicecomponents will be able to operate in a separate life- cycle. Loose Coupling: The Service Consumer Component will define its specificationindependent of the Service Provider Component. The responsibility of aligning the twospecifications is up to the Assembler component, which bridges the gap between twoworlds. Invokable interfaces: The Service interfaces will be invokable either locally orremotely. At the architecture level, we dont really care how the interface is invoked. Communication Protocol: A Service will be invokable by variety of protocol.The choice of protocol will not restrict the behaviour of the Service. Binding to a specificprotocol must take place at run-time/deployment-time, and not at the design ordevelopment time.

Interoperability is the most important principle of SOA. This can be realized through theuse of web services, which allows different distributed web services to run on a variety of

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software platforms and hardware architectures. The Java programming languagerepresents the ideal platform for developing portable and interoperable web services.

Interoperability and portability start with the standard specifications themselves.TheJ2EE 1.4 and Java WSDP 1.5 platforms include the technologies that supportSOAP, WSDL, UDDI, and ebXML. This core set of specifications which are used to

describe, publish, enable discovery, and invoke web services are based on XML andXML Schema. The J2EE1.4 and Java WSDP 1.5 platforms ensure that applications areportable across J2EE implementations and also that web services are interoperable.

The Enterprise Service Bus (ESB) is an important part of an SOA infrastructure, since itprovides a standards-based messaging layer with capabilities for services virtualization.ESB is the backbone of SOA that acts as a message broker providing a messagequeuing system using industry standard specifications for messaging such as SOAP, orJMS (Java Message Service).

ESB Architecture

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