Web Services SOA Tutorial

Introduction to Web Services Technology

What is Web Services

Programming language and platform independent infrastructure for loosely-coupled, App2App communication over the Internet(Globe). 

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A web service is a piece of business logic, located somewhere on the Internet, that is accessible through standard-based Internet protocols such as HTTP or SMTP. 

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Web services framework is an XML-based distributed object/service/component system. Intended to support machine-to-machine interactions over the network.

Characteristics of Web Services

A web service has special behavioral characteristics:

XML-based: As a data transport, XML eliminates any networking, operating system, or platform binding that a protocol has.

Loosely coupled: The web service interface can change over time without compromising the client's ability to interact with the service.

Adopting a loosely coupled architecture tends to make software systems more manageable and allows simpler integration between different systems.

Supports Remote Procedure Calls (RPCs): Web services allow clients to invoke procedures, functions and methods on remote objects using an XML-based protocol.

Remote procedures expose input and output parameters that a web service must support

Ability to be synchronous or asynchronous: 

Synchronicity refers to the binding of the client to the execution of the service. In synchronous invocations, the client blocks and waits for the service to complete its operation before continuing.

Asynchronous operations allow a client to invoke a service and then execute other functions. Asynchronous clients retrieve their result at a later point in time, while synchronous clients receive their result when the service has completed.

Asynchronous capability is a key factor in enabling loosely coupled systems.

Supports document exchange: 

Web services support the transparent exchange of documents to facilitate business integration.

Why Web Service?

Interoperable - Connect across heterogeneous networks using ubiquitous web-based standards.

Economical - Recycle components, no installation and tight integration of software

Automatic - No human intervention required even for highly complex transactions.

Accessible - Legacy assets & internal apps are exposed and accessible on the web.

Available -Services on any device, anywhere, anytime. 

Scalable -No limits on scope of applications and amount of heterogeneous applications.

There are two kind of approach generally used to implement a Web Services: 

1. Code First Approach (Buttom-Up) :- In the Code First Approach, development of the service is started from a code. So the developer can write a service without knowing anything about WSDL. Code First approach is simple, less time consuming and easy to use for people who are not familiar with Web Services standards because WSDL is somewhat hard to understand and use for a beginner. Code First is a good approach to convert a lagacy code into a Web Services. 

2. Contract First Approach (top-Down Approach) :- In the Contract First Approach, development of the service is started from a WSDL definition, which becomes a contract between the service provider and the client. Once WSDl is finalize between the business, the client side and server work can start parallel on basis of finalized WSDL. This approach is more complex compared to Code First Approach and also it requires an in depth understanding of WEB Services. But it is the more popular and recommended. 

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