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WSDL

The SOAP message itself is contained inside an

envelope

, which is used to transfer the Web service call to

and from the server. A typical SOAP message looks like this:

<soap:Envelope xmlns:n=”custom namespace goes here”

xmlns:soap=”http://schemas.xmlsoap.org/soap/envelope/”

xmlns:soapenc=”http://schemas.xmlsoap.org/soap/encoding/”

xmlns:xs=”http://www.w3.org/2001/XMLSchema”

xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance”>

<soap:Body soap:encodingStyle=”http://schemas.xmlsoap.org/soap/encoding/”>

</soap:Body>

</soap:Envelope>

In the case of the client sending the message, the XML in

<soap:Body/>

includes a method to call and

parameters. When the server sends the message,

<soap:Body/>

includes the result(s) of the call. The

result can be a single value or a complex data type with multiple values.

Naturally, it is important that the client sends the SOAP message in the correct format, but how does a

developer know how to format the message? This is where WSDL comes in.

WSDL

Web Services Description Language (WSDL, pronounced wizdel) is used to describe the capabilities, for-

mat, and other important information about Web services. WSDL files define the various operations a

Web service provides.

Operations

are specific remote functions that can be called for a given service (a Web

service can have one or more operations). It helps to think of a Web service as an object with one or more

methods; the object itself represents the service whereas the operations are considered the methods.

The basic sections of a WSDL file are the following:

Types — Defines the types used for the Web service calls. These types are based on XML

Schema data types and can represent simple types — such as numbers or strings — or complex

types, similar to objects that have properties.

Messages — Defines the input arguments and the output value for a given operation. Each

operation gets two message definitions, one for the operation request and one for the response.

Port Type — Defines the operations that are available from the Web service.

Bindings — Defines the format of the messages sent and received with each operation.

Service — Defines how to access the Web service operations.

A standard WSDL file has the following format:

<definitions name=”name_of_service”

targetNamespace=”target_namespace”

xmlns:tns=”location_of_wsdl”

xmlns:xsd=”http://www.w3.org/2001/XMLSchema”

xmlns:soap=”http://schemas.xmlsoap.org/wsdl/soap/”

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