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 arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable ...

-based interface description language that is used for describing the functionality offered by a web service. 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 similar to that of a

type signature In computer science, a type signature or type annotation defines the inputs and outputs for a function, subroutine or method. A type signature includes the number, types, and order of the arguments contained by a function. A type signature is typ ...

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 H ...

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 A network address is an identifier for a node or host on a telecommunications network. Network addresses are designed to be unique identifiers across the network, although some networks allow for local, private addresses, or locally administer ...

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 of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are use ...

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 constra ...

to provide Web services over the

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

. 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 In computer science and computer programming, a data type (or simply type) is a set of possible values and a set of allowed operations on it. A data type tells the compiler or interpreter how the programmer intends to use the data. Most progra ...

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 The Hypertext Transfer Protocol (HTTP) 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 We ...

. The current version of the specification is 2.0; version 1.1 has not been endorsed by the W3C 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 and led by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working t ...

. 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 web services, 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 ...

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.

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 the pioneer tool to construct SWSDL's successfully.

Example WSDL file

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

History

WSDL 1.0 (Sept. 2000) was developed by IBM,

Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washin ...

, and

Ariba SAP Ariba is an American software and information technology services company located in Palo Alto, California. It was acquired by German software maker SAP SE for $4.3 billion in 2012. Company beginnings Ariba (now SAP Ariba) was founded in ...

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

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

Subset WSDL

Example WSDL file

History

Security considerations

See also

References

External links