Web Services Description Language

Web Services Description Language (WSDL) plays an important role in the overall Web services architecture since it describes the complete contract for application communication. WSDL is a standard specification for describing services. It describes the service details in the basic information which is needed to make requests, regardless of run-time implementation details. WSDL also defines an XML format, for describing network services as a set of endpoints that operate on messages that contain either document-oriented or procedure-oriented information.

WSDL allows a service provider to specify the following characteristics of a Web service:

The name of the Web service and addressing information

The protocol and encoding style to be used when accessing the public operations of the Web service

The type information such as operations, parameters, and data types comprising the interface of the Web service

WSDL documents allow developers to expose their applications as network-accessible services on the Internet. Through UDDI, other applications can discover WSDL documents and bind with them to execute transactions or perform other business processes.

WSDL Basics

A WSDL definition is an XML document with a root definition element from the http://schemas.xmlsoap.org/wsdl/ namespace. The definitions element may contain several other elements including types, message, portType, binding, and service, all of which come from the http://schemas.xmlsoap.org/wsdl/ namespace. The following Table 1 provides brief definitions for each of these core WSDL elements and the remaining sections discuss them in more detail.

Universal Description, Discovery, and Integration (UDDI)

Universal Description, Discovery, and Integration (UDDI) is based on a common set of industry standards, including HTTP, XML, XML Schema, and SOAP. It provides an infrastructure for a Web Services-based software environment for both publicly available services and services only exposed internally within an organization. UDDI provides the definition of the services and its supporting information for description and discovery of services like:

• Businesses, organizations, and other Web Services providers
• Available Web Services in the registry
• Technical interfaces used to access those services

The idea is to "discover" organizations and the services that organizations offer, much like using a phone book or dialing information. UDDI comprised of more than 300 business and technology leaders working together to enable companies and applications to quickly, easily, and dynamically find, and use Web Services. UDDI Business Registry system consists of three directories:

UDDI white pages: basic information such as a company name, address, and phone numbers, as well as other standard business identifiers like Dun & Bradstreet and tax numbers. Basic information about the company and its business. A Unique identifiers like company tax IDs information allows others to discover your web service based upon your business identification.

UDDI yellow pages provide detailed business data, organized by relevant business classifications. The UDDI version of the yellow pages classifies businesses according to the newer NAICS (North American Industry Classification System) codes, Yellow pages contain more details about the company. They include descriptions of the kind of electronic capabilities the company can offer to anyone who wants to do business with it. Yellow pages uses commonly accepted industrial categorization schemes, industry codes, product codes, business identification codes and the like to make it easier for companies to search through the listings and find exactly what they want.

UDDI green pages: information about a company's key business processes, such as operating platform, supported programs, purchasing methods, shipping and billing requirements, and other higher-level business protocols. Green pages contains technical information about a web service. A green page allows someone to bind to a Web service after it's been found.

Private UDDI

Registries As an alternative to using the public federated network of UDDI registries available on the Internet, companies or industry groups may choose to implement their own private UDDI registries. For example, a large company may set up its own private UDDI registry for registering all internal web services. These exclusive services are designed for the sole purpose of allowing members of the company or of the industry group to share and advertise services amongst themselves. Regardless of whether the UDDI registry is a part of the global federated network or a privately owned and operated registry, the one thing that ties them all together is a common web services API for publishing and locating businesses and services advertised within the UDDI registry.