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Arvind Padmanabhan

WEB Services are self-contained, self-describing, modular applications that can be published, located, and invoked across the Web. Web services link servers over the Internet to exchange data and combine information in new ways. Web service interoperability goals are to provide seamless and automatic connections from one software application to another, irrespective of its platform or environment. Web services have been touted as the solution to many challenges corporate IT organisations face, enabling various types of application integration. Hewlett-Packard was the first to champion Web Services in mid-1999.

Web Services are an emerging technology that helps expose securely business logic beyond the firewall. Web Services will enable application-to-application e-marketplace interaction, removing the inefficiencies of human intervention. The basic platform for Web Services is XML plus HTTP. HTTP is a ubiquitous protocol, running practically everywhere on the Internet. XML provides a Meta language in which you can write specialised languages to express complex interactions between clients and services or between components of a composite service. Behind the facade of a web server, the XML message gets converted to a middleware request and the results converted back to XML.

A brief description of the platform elements:

SOAP (remote invocation): Simple Object Access Protocol is a way to create widely distributed, complex computing environments that run over the Internet using existing Internet infrastructure. SOAP is about applications communicating directly with each other over the Internet in a very rich way.

UDDI (trader, directory services): Universal Description, Discovery, and Integration is a comprehensive, open industry initiative enabling businesses to (1) discover each other, and (2) define how they interact over the Internet and share information in a global registry architecture. UDDI is the building block that will enable businesses to quickly, easily and dynamically find and transact with one another via their preferred applications.

WSDL (expression of service characteristics): Web Services Description Language is an XML format for describing network services as a set of endpoints operating on messages containing either document-oriented or procedure-oriented information. Consider a situation where you want to access a third-party remote service over the Internet for, say, credit card authorisation. To do this, you need to know certain things, such as the signature method; the protocol to be used, the network address; and the data format. This is precisely what the Web Services Description Language (WSDL) specification defines in an XML format.

A WSDL document uses the following elements in the definition of network services:

Types — a container for data type definitions using some type system (such as XSD— XML Signature Verification Response Schema).

Message — an abstract, typed definition of the data being communicated.

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.

XLANG/XAML (transactional support for complex Web transactions involving multiple Web Services): Automation of business processes based on Web services requires a notation for the specification of message exchange behaviour among participating Web services. This document specifies such a notation. XLANG is expected to serve as the basis for automated protocol engines that can track the state of process instances and help enforce protocol correctness in message flows. XLANG is a notation for expressing the compensatory actions for any request that needs to be undone.

The Web services infrastructure can leverage XLANG specifications to perform complex undo operations. Transaction Authority Markup Language (XAML) is a vendor-neutral standard that enables the coordination and processing of online transactions in the rapidly emerging world of XML web. XAML is intended to be a completely open standard for web-based business transactions. The standard defines a set of XML message formats and interaction models Web services can use in order to provide business-level transactions that span multiple parties across the Internet.

XKMS: XML Key Management Specification is the work carried out by Microsoft and Verisign to support authentication and registration.

XFS: The XMethods filesystem service enables posting and reading files via a SOAP interface. This system enables developers create services that utilise centralised, persistent data. Ideally, this type of file system can be used to centralise the storage of information that can be accessed by multiple nodes.

ebXML: Provides an open XML-based infrastructure enabling the global use of electronic business information in an interoperable, secure, and consistent manner by all parties.

The key benefits of Web Services are:

As opposed to packaged products, Web Services can be delivered and paid for as streams of services, and allow ubiquitous access from any platform. Web services allow for encapsulation. Components can be isolated such that only the business-level services are exposed. This results in decoupling between components and more stable and flexible systems.

Dynamic business interoperability

New business partnerships can be constructed dynamically and automatically since Web Services ensure complete interoperability between systems. Accessibility business services can be completely decentralised and distributed over the Internet and accessed by a wide variety of communications devices.

Efficiencies Businesses can be released from the burden of complex, slow and expensive software development and focus instead on value added and mission critical tasks. Web services constructed from applications meant for internal use can be easily exposed for external use without changing code.

Universally agreed specifications

Web Services are based on universally agreed specifications for structured data exchange, messaging, discovery of services, interface description, and business process orchestration. Legacy integration, greater agility and flexibility from increased integration between legacy systems.

There are several important business reasons why the use of web services are applicable:

Cost: With the open standards based approach, we would definitely be able to protect our investments in software that is Web services-enabled, thereby translating into huge cost savings. This can be applied equally to applications and future projects.

Strong vendor support: This is an absolute first for Web services. Never before have vendors agreed so whole-heartedly.

Integration with other electronic business protocol: With ebXML and RosettaNet standards being accepted, it will not be long before Web Services could be used to enable electronic business with other protocols.

Developer productivity: Since it is based on open-standards and several tools are available, developers today should feel more comfortable using Web services.

However, there are some limitations too:

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