Heralding the arrival of Web Services

Avijeet Dash and Satybrata Dash

This series on Web Services will begin with a ‘big picture’ about XML and
Web Services and will gradually delve into the technical details and
implementation of XML and Web Services. We will substantiate each article of the
series by proving examples and references to external resources. We also feel
that reader’s contribution in giving us suggestions and feedbacks will be
invaluable in making this Web Services series more interesting and useful.

Introduction

Web Services are the services available over Internet. The services are
applications implemented in any language, but seen by the outside world through
standardized XML interface. Similarly anybody can avail the service through a
XML request. So, Web Service heralds the beginning of a new technology era, in
which applications can communicate with each other in the Web through XML based
messaging and interface.

Web Service actors

The three prime actors of Web Services are

1. Service provider
   
   
A Service provider defines a public interface of its services and then
registers the services in public service registry so as to make the services
available over the Web.
2. Service registry
   
   All public services have to be registered in a public service registry
   so that service finders can locate them. Service ddRegistry thus acts as a
   repository of Web Services and it brokers between Service Provider and Service
   Requestor.
3. Service requestor
   
   Service requestor first locates the service provider through the
   service registry and then establishes direct a communication channel with the
   service provider to avail the service. So the service requestor acts as a
   client to the service provider.

Significance of Web Services

1. Service based application:
   
   
Product applications can be offered to clients as services. For
example, let’s say Microsoft offers MS Word as a service, then the clients
don’t have to install Microsoft office on their desktop to draft a document,
instead, then can simply go to the Website of Microsoft, draft a letter and
then save it in Microsoft’s database so that they can open the document
anytime from anywhere in the world. Similarly, everything can be offered as a
service over the Web.
2. Application based Web:
   
   Human beings are the prime actor in today’s Web world. There exists no
   simple mechanism for applications to talk to each other over web. For example, a
   power company needs to get weather data from weather department. The weather
   department is Web-enabled, so users can visit the Website and look at the
   temperature of a city, but it doesn’t expose any APIs(application programming
   interfaces), so other applications can’t find the weather data online. So, Web
   Services allows the weather department- power company interaction by exposing
   the services in XML standard format.
3. Enterprise Application Integration made simpler:
   
   EAI is still a nightmare for the new breed of heterogeneous
   applications. Although, there exists many third party adapters for EAI
   integration, there exists no standard for inter-application communication. But,
   that scene might change with Web Services, as leading companies of the world
   like Microsoft, Sun and IBM are trying to make Web Services a standard. So, the
   service implementation need not be tied to any language or operating system.
   Service providers can host the service in a legacy S/390 mainframe, where as
   service requestors can run their J2EE application hosted in a Weblogic Server.
   It is possible to decouple the service providers and service requestors by
   providing a common XML based messaging interface.

XML is the underlying technology behind all technologies involved in Web
Services. So, we will begin with basics of XML in this series before moving on
to Web Services technologies such as SOAP, WSDL and UDDI.

We will focus on providing various java implementation techniques of Web
Services in different application servers such as Tomcat, Weblogic, WebSphere.
We will also provide implementation procedures of Web Services in .Net
environment.

 

(The authors are senior developers at MindTree Consulting. They can be reached
at avijeetd@mindtree.com and satyabrata_dash@mindtree.com).