Web Services.

With a sudden increase in awareness about the terms "web services", "WSDL:', "XML:'  "SOAP", to name but a few, there has been a corresponding increase in the number of curious people who want to know what all the fuss is about.

Today's most popular search engine, Google, exposes its search application programming interface (API) through a Web service, giving Web developers the opportunity to utilize such search capabilities within their applications. E-commerce giants such as. Amazon and eBay Find also expose their product catalogues and search facilities via Web services. So what is the hype all about? Web services, in the general meaning of the term, are services offered by one application to other applications via the World Wide Web. Clients of these services can aggregate them to form an end-user application, enable business transactions, or create new Web services. Utilities of this kind are built according to Extensible Markup Language (XML), Simple Object Access Protocol (SOAP), Web Service Definition Language (WSDL), and Universal Description, Discovery and Integration (UDDI) specifications. They are prevalent and portable, covering every operating system and programming language. These standards provide the foundation for application integration and aggregation that companies are starting to use in order to create solutions and improve the usefulness and interoperability of their applications.

In today's world of extreme competition on the business front, information exchange and efficient.
Publish ,communication IS the need of the day. Information technology has grown by leaps and bounds and has been sustained not because it seems savvy, but because it allows businesses to function more efficiently. This need for information exchange brings in another need, that of making this information selectively visible, and of allowing its visibility to be changed on the fly.
The revolution of computerizing the services of companies gave rise to isolated computer systems. Each company had software developed and customized to its specific needs. However, with the frequent growth in business, the need to share information stored in these isolated systems has become inevitable. The advent of the internet solved this problem to some extent but simultaneously created many security loopholes, making the owners of said information uneasy about the scope of its availability. Hence, it became imperative that for better B2B (business-to-business) communications, these systems have the ability to link to one another, grant permissions through a system other than the internet,and network with each other as though they exist on an intranet. The concept of Web services is probably not the first solution to such a problem. The usage of techniques and technologies such as Remote Method Invocation (RMI), Component Object Model (COM), Common Object Request Broker Architecture (CORBA), Electronic Data Interchange (EDI), and Electronic Business Extensible Markup Language (ebXML) also addresses the same problem spaces.
If we take a look at the past we can see that the paradigm of distributed computing was born with the advent of computer networks. Applications were split first into two parts with one part (the client) initiating a distributed activity, and the other part (the server) carrying out that activity.

This decentralisation minimised bottlenecks by distributing workloads across multiple systems. But this two-tier architecture had its limits. Frequent failovers and scalability issues introduced a third tier which separate_ an application into a presentation part, a middle tier containing the business logic, and a third tier dealing with the data.

To keep developers away from low-level tasks such as data conversion between two different machines, a new layer of software hit the market. This middleware masked the differences between various kinds of hosts by sitting on top of the host's operating system and networking services and offering its services to the applications above. The first generation of middleware was based on a procedural programming model and was superseded by the introduction of object-oriented programming models thanks to middleware such as CORBA, DCOM, and RMI. CORBA is an open standards-based solution for distributed computing and is defined by the Object Management Group (OMG) in its Object Management Architecture (OM A) specification. OMG is an industry consortium which specified the Internet InterORB Protocol (IIOP) which is the standard communication protocol between Object Request Brokers (ORB). It was first released in 1991 and defined how objects can interact over a special interface bus called ORB. The primary advantage of CORBA is that clients and servers can be written in any programming language and can run on almost any computer, operating system, or network.

RMI facilitates object function calls between Java Virtual Machines (JVMs). RMI uses the Java Remote MethodProtocol (JRMP) for communication purposes. The drawback of using RMI is that it can only be used with Java on both sides of the connection. On the other hand, Microsoft's Distributed Component Object Model (DCOM) is associated with Microsoft operating systems, but ports exist for Unix and Macintosl:1 systems as well. CORBA, RMI and DCOM are good examples of middleware that may have been an excellent platform to deploy applications, but that lack in serving as good integration technology.

Web services go beyond the prior technologies by providing a text-based message protocol that can be transported using the ubiquitous internet and most importantly, which is supported by all major vendors. The middleware discussed so far used some type of binary protocol for communication. Web services however, use XML on top of the Hypertext Transfer Protocol (HTTP), which has become a widely accepted format for exchanging data and its corresponding semantics. It is a fundamental building block for nearly every layer used for Web services.

Although Web services architecture can be considered independently of any particular standards, a number of key industry leaders have worked to develop a set of XML-based open standards on which Web services have been implemented. XML is a cross-platform, extensible text-based standard for representing data. WSDL was first developed in order to create the Web service description. It describes a service as a set of "ports" that groups possible interactions between the application and the Web service. A WSDL document. provides the potential information on interactions with a Web service but does not explain how to communicate that information. For this purpose, WSDL allows a "binding" known as SOAP to be specified. SOAP is a standard for XMLbased information exchange between distributed applications. Although other transports are possible, SOAP is typically transmitted over HTTP, thereby providing a platform for communication between Web services.

Web services can be described by the help of WSDL and SOAP and can be used from an application. But, how can anyone find what sort of Web services are , available in the first place? This is the purpose of UDDI, which is a specification for distributed registries of Web services. A UDDI Web services registry is itself a Web service which can be accessed via SOAP from an application that wishes to discover Web services. UDDI specifies interfaces for applications to publish Web services (as WSDL documents) and to discover Web services (via their WSDL documents).

Since the introduction of XML in 1998, ,Web service technology has steadily gathered momentum. Both Microsoft and IBM were pioneering forces behind its implementation and their work together has seen a number of developments, most notably SOAP and WSDL It is important however, that the factors contributing to successful Web service growth are harnessed in order to ensure a prosperous future for Web services.

_{source Spider Mag.}