Web Services..
Web services is any application (service) running on any
platform, coded in any language which makes itself available over the internet,
example a web site is available for end user consumption a web service is available for application consumption, basically
applications irrespective of platform/programming language communicating with
each other over the network/internet via the web services protocols.
Example an application coded in Java can call
(communicate) a web service coded in .Net and vice-versa. Web Service is based on the use of Extensible Markup
Language (XML). XML is designed to share, store, carry and exchange data and is
not designed to display data. XML helps systems share structured data, is
pervasive and is a language to share metadata.
XML is not restricted to web services only and is used
widely in Web 2.0/AJAX. Majority of the software vendors now make available
there applications via web services and the current trend is to eliminate the traditional client-server model and make the
applications available to any subscriber (client) over http/https only.
The services shared via the web service is called a
contract, this is provided as an XML document known as WSDL (Web Service Description Language), This WSDL
document is shared with the external users, the customers.
As shown in the below diagram the application calls are
first converted into a specific XML message and then transmitted over the
network. The conversion of program calls/messages (in any language) to this XML
message is done by SEI (Service Endpoint Interface).The data types exchanged between
web services is in a specific XML format defined via SOAP (Simple Object Access
Protocol). This SOAP message is sent over the network/internet to the web
services provider.
In short the application calls are converted via SEI to
SOAP which then uses WSDL to connect to the Web Services provider.
If any company wants to introduce their services to the public
internet they do so by registering there
web services to UDDI (Universal Discovery Description and
Integration), the UDDI is like a yellow pages for web services, any consumer
just queries this registry, gets the requisite WSDL and uses that web service.
Web services communicates either via SOAP (more popular)
or REST (Representational State Transfer) protocol, though there are
differences in specifics but in general both provide the same functionality
In the above diagram, If Company A wants to subscribe to
the Web Services of Company B, the application at Company A would call the
specific function/method, the SEI would convert this call to a SOAP message and
using the WSDL contract XML file will make a http/https POST request to the Web
Service Endpoint at Company B, The Web Service EndPoint at Company B would then
convert the SOAP message via SEI to format understood by the application
at Company B and would then respond with the appropriate message, this response would again follow
the same process as followed by Company A.
We can see that via Web Services an application coded in
any language can communicate with application coded in any other language and
vice-versa, all we need is the SEI to convert/de-convert the messages to/from
SOAP and the Web Service Contract (WSDL) file in XML. The SEI basically runs on
top your application and is transparent to the application.
