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
• 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
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 WSDL document uses the following elements to define
• 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