| Web Services Description Language | |
|---|---|
 | |
| Filename extension | .wsdl |
| Internet media type | application/wsdl+xml |
| Developed by | World Wide Web Consortium |
| Contained by | XML |
| Standard | 2.0 Recommendation |
TheWeb Services Description Language (WSDL/ˈwɪzdəl/) is anXML-basedinterface description language that is used for describing the functionality offered by aweb service.[citation needed] The acronym is also used for any specific WSDL description of a web service (also referred to as aWSDL 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 atype signature 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".
The WSDL describes services as collections of networkendpoints, orports. The WSDL specification provides anXMLformat 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 anetwork 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 withSOAP and anXML Schema to provide Web services over theInternet. A client program connecting to a Web service can read the WSDL file to determine what operations are available on the server. Any specialdatatypes 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 overHTTP.
The current version of the specification is 2.0; version 1.1 has not been endorsed by theW3C but version 2.0 is aW3C recommendation.[1] WSDL 1.2 was renamed WSDL 2.0 because of its substantial differences from WSDL 1.1. By accepting binding to all theHTTP request methods (not only GET and POST as in version 1.1), the WSDL 2.0 specification offers better support forRESTfulweb services, and is much simpler to implement.[2][3] However support for this specification is still poor insoftware development kits for Web Services which often offer tools only for WSDL 1.1.[needs update][citation needed] For example, the version 2.0 of theBusiness Process Execution Language (BPEL) only supports WSDL 1.1.
| WSDL 1.1 Term | WSDL 2.0 Term | Description |
|---|---|---|
| Service | Service | Contains a set of system functions that have been exposed to the Web-based protocols. |
| Port | Endpoint | Defines the address or connection point to a Web service. It is typically represented by a simple HTTPURL string. |
| Binding | Binding | Specifies the interface and defines theSOAP binding style (RPC/Document) and transport (SOAP Protocol). The binding section also defines the operations. |
| PortType | Interface | Defines a Web service, the operations that can be performed, and the messages that are used to perform the operation. |
| Operation | Operation | Defines the SOAP actions and the way the message is encoded, for example, "literal." An operation is like a method or function call in a traditional programming language. |
| Message | — | Typically, a message corresponds to an operation. The message contains the information needed to perform the operation. Each message is made up of one or more logical parts. Each part is associated with a message-typing attribute. The message name attribute provides a unique name among all messages. The part name attribute provides a unique name among all the parts of the enclosing message. Parts are a description of the logical content of a message. In RPC binding, a binding may reference the name of a part in order to specify binding-specific information about the part. A part may represent a parameter in the message; the bindings define the actual meaning of the part. Messages were removed in WSDL 2.0, in whichXML schema types for defining bodies of inputs, outputs and faults are referred to simply and directly. |
| Types | Types | Describes the data. TheXML Schema language (also known asXSD) is used (inline or referenced) for this purpose. |
<?xml version="1.0" encoding="UTF-8"?><descriptionxmlns="http://www.w3.org/ns/wsdl"xmlns:tns="http://www.tmsws.com/wsdl20sample"xmlns:whttp="http://schemas.xmlsoap.org/wsdl/http/"xmlns:wsoap="http://schemas.xmlsoap.org/wsdl/soap/"targetNamespace="http://www.tmsws.com/wsdl20sample"><documentation>ThisisasampleWSDL2.0document.</documentation><!-- Abstract type --><types><xs:schemaxmlns:xs="http://www.w3.org/2001/XMLSchema"xmlns="http://www.tmsws.com/wsdl20sample"targetNamespace="http://www.example.com/wsdl20sample"><xs:elementname="request">...</xs:element><xs:elementname="response">...</xs:element></xs:schema></types><!-- Abstract interfaces --><interfacename="Interface1"><faultname="Error1"element="tns:response"/><operationname="Get"pattern="http://www.w3.org/ns/wsdl/in-out"><inputmessageLabel="In"element="tns:request"/><outputmessageLabel="Out"element="tns:response"/></operation></interface><!-- Concrete Binding Over HTTP --><bindingname="HttpBinding"interface="tns:Interface1"type="http://www.w3.org/ns/wsdl/http"><operationref="tns:Get"whttp:method="GET"/></binding><!-- Concrete Binding with SOAP--><bindingname="SoapBinding"interface="tns:Interface1"type="http://www.w3.org/ns/wsdl/soap"wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP/"wsoap:mepDefault="http://www.w3.org/2003/05/soap/mep/request-response"><operationref="tns:Get"/></binding><!-- Web Service offering endpoints for both bindings--><servicename="Service1"interface="tns:Interface1"><endpointname="HttpEndpoint"binding="tns:HttpBinding"address="http://www.example.com/rest/"/><endpointname="SoapEndpoint"binding="tns:SoapBinding"address="http://www.example.com/soap/"/></service></description>
WSDL 1.0 (Sept. 2000) was developed byIBM,Microsoft, andAriba 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 andSDL (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:
Subset WSDL (SWSDL)[4] 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[5] is a tool that can identify subset operations in a WSDL file to construct a subset WSDL.
Since WSDL files are an XML-based specification for describing a web service, WSDL files are susceptible to attack.[6] 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.