Web Services

The specifications that define Web services are intentionally modular, and as a result there is not a single document that contains them all. Additionally, there is neither a single, nor a stable set of specifications. There are a few “core” specifications that are supplemented by different groups (as the circumstances and choice of technology dictate) like XML , SOAP have come from W3C while WSDL and UDDI are provided by OASIS.

The web services platform can be thought of as:

HTTP + SOAP (XML-based protocol) + WSDL (XML-based format) + UDDI. Where

• HTTP is a ubiquitous protocol supported everywhere on the Internet.

• SOAP is needed for remote procedure calls. It is an XMLbased format, that provide” bindings” with underlying
network protocols like HTTP, HTTPs, SMTP, XMPP etc. A
SOAP call is packaged as the body of an HTTP request.

• WSDL is an expression of service characteristics that
allows service interfaces to be described, along with the
details of their bindings to specific protocols. WSDL is
used to describe what a web service can do, where it
resides, and how to invoke it.

• UDDI acts as the trader, directory service etc. It is required for publishing and discovering metadata about Web services, that enables applications to find Web services, either at design time or runtime.

Web Services model
Examples of few web services
Google’s Web Service - access the Google search engine



• Amazon’s Web Service - access Amazon’s product
• SalCentral - WSDL / SOAP Web services search engine

Description of the Web Services Standards:

I WSDL (Web Services Description Language)
At the early stages, defining the standard behavior of the both ends of the pipe over the web using traditional RPC was highly problematic. It immensely required some fresh changes to introduce. Hence, Web Services Description Language (WSDL for short and often pronounced wisdel) took initiative to deal with such issues.

WSDL uses XML to define the interfaces to the existing or to the new application or anywhere in between. WSDL describes what a web service can do, where it resides, and how to invoke it. It defines the syntax, the semantics, and all the various administrative aspects of a web services remote procedure call.

WSDL defines services as a collection of network endpoints (ports). In WSDL the abstract definition of endpoints and messages is separated from their concrete network deployment and data format bindings. This allows reuse of abstract definitions of messages (which are abstract descriptions of the data being exchanged) and port types (which are abstract collections of operations). The concrete protocol and data format specifications for a particular port type constitute a reusable binding. A port is defined by associating a network address with a reusable binding and a collection of ports define a service.

A WSDL document uses the following elements to define
network services:

Types - a container for data type definitions using some
type system (such as XSD).

Message - an abstract, typed definition of the data being

Operation - an abstract description of an action supported by the service.

Port Type - an abstract set of operations supported by one or more endpoints.

Binding - a concrete protocol and data format specification for a particular port type.

Port - a single endpoint defined as a combination of a
binding and a network address.

Service - a collection of related endpoints. In simple words, WSDL is a template which shows how

July 2007 | Java Jazz Up |36
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