The Web Services Description Language (WSDL ) is an

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing data. It defines a set of rules for encoding electronic document, documents in a format that is both human-readable and Machine-r ...

-based interface description language that is used for describing the functionality offered by a

web service A web service (WS) is either: * a service offered by an electronic device to another electronic device, communicating with each other via the Internet, or * a server running on a computer device, listening for requests at a particular port over a n ...

. The acronym is also used for any specific WSDL description of a web service (also referred to as a ''WSDL file''), which provides a machine-readable description of how the service can be called, what parameters it expects, and what data structures it returns. Therefore, its purpose is roughly like a

type signature In computer science, a type signature or type annotation defines the inputs and outputs of a function, subroutine or method. A type signature includes the number, types, and order of the function's arguments. One important use of a type sign ...

in a programming language. The latest version of WSDL, which became a W3C recommendation in 2007, is WSDL 2.0. The meaning of the acronym has changed from version 1.1 where the "D" stood for "Definition".

Description

The WSDL describes services as collections of network endpoints, or

port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Hamburg, Manch ...

s. The WSDL specification provides an

format for documents for this purpose. The abstract definitions of ports and messages are separated from their concrete use or instance, allowing the reuse of these definitions. A port is defined by associating a network address with a reusable binding, and a collection of ports defines a service. Messages are abstract descriptions of the data being exchanged, and port types are abstract collections of supported operations. The concrete protocol and data format specifications for a particular port type constitutes a reusable binding, where the operations and messages are then bound to a concrete network protocol and message format. In this way, WSDL describes the public interface to the Web service. WSDL is often used in combination with

SOAP Soap is a salt (chemistry), salt of a fatty acid (sometimes other carboxylic acids) used for cleaning and lubricating products as well as other applications. In a domestic setting, soaps, specifically "toilet soaps", are surfactants usually u ...

and an

XML Schema An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself. These constrai ...

to provide Web services over the

Internet The Internet (or internet) is the Global network, global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a internetworking, network of networks ...

. A client program connecting to a Web service can read the WSDL file to determine what operations are available on the server. Any special datatypes used are embedded in the WSDL file in the form of XML Schema. The client can then use SOAP to actually call one of the operations listed in the WSDL file, using for example XML over

HTTP HTTP (Hypertext Transfer Protocol) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, wher ...

. The current version of the specification is 2.0; version 1.1 has not been endorsed by the

W3C The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working together in ...

but version 2.0 is a

W3C recommendation The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working together in ...

. WSDL 1.2 was renamed WSDL 2.0 because of its substantial differences from WSDL 1.1. By accepting binding to all the HTTP request methods (not only GET and POST as in version 1.1), the WSDL 2.0 specification offers better support for

RESTful REST (Representational State Transfer) is a software architectural style that was created to describe the design and guide the development of the architecture for the World Wide Web. REST defines a set of constraints for how the architecture of ...

s, and is much simpler to implement. However support for this specification is still poor in

software development kit A software development kit (SDK) is a collection of software development tools in one installable package. They facilitate the creation of applications by having a compiler, debugger and sometimes a software framework. They are normally specific t ...

s for Web Services which often offer tools only for WSDL 1.1. For example, the version 2.0 of the Business Process Execution Language (BPEL) only supports WSDL 1.1.

Example WSDL file

This is a sample WSDL 2.0 document. ... ...

History

WSDL 1.0 (Sept. 2000) was developed by

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

, and

Ariba The Royal Institute of British Architects (RIBA) is a professional body for architects primarily in the United Kingdom, but also internationally, founded for the advancement of architecture under its royal charter granted in 1837, three suppl ...

to describe Web Services for their SOAP toolkit. It was built by combining two service description languages: NASSL (Network Application Service Specification Language) from IBM and SDL (Service Description Language) from Microsoft. WSDL 1.1, published in March 2001, is the formalization of WSDL 1.0. No major changes were introduced between 1.0 and 1.1. WSDL 1.2 (June 2003) was a working draft at W3C, but has become WSDL 2.0. According to W3C: WSDL 1.2 is easier and more flexible for developers than the previous version. WSDL 1.2 attempts to remove non-interoperable features and also defines the HTTP 1.1 binding better. WSDL 1.2 was not supported by most SOAP servers/vendors. WSDL 2.0 became a W3C recommendation in June 2007. WSDL 1.2 was renamed to WSDL 2.0 because it has substantial differences from WSDL 1.1. The changes are the following: *Added further semantics to the description language *Removed message constructs *Operator overloading not supported *PortTypes renamed to interfaces *Ports renamed to endpoints

Subset WSDL

Subset WSDL (SWSDL) is a WSDL with the subset operations of an original WSDL. A developer can use SWSDL to access Subset Service, thus handle subset of web service code. A Subset WSDL can be used to perform web service testing and top down development. Slicing of a web service can be done using a Subset WSDL to access Subset Service. Subset Service can be categorized into layers using SWSDL. SWSDLs are used for Web service analysis, testing and top down development. AWSCM is a tool that can identify subset operations in a WSDL file to construct a subset WSDL.

Security considerations

Since WSDL files are an XML-based specification for describing a web service, WSDL files are susceptible to attack. To mitigate vulnerability of these files, limiting access to generated WSDL files, setting proper access restrictions on WSDL definitions, and avoiding unnecessary definitions in web services is encouraged.

Description

Example WSDL file

History

Subset WSDL

Security considerations

See also

References

External links