Difference between SOAP and WSDL

A web service is a way for different applications or systems to communicate and share data over the internet, even if they’re built on different platforms or languages. SOAP and WSDL are both Extensible Markup Language or XML-based technologies used in such web services. SOAP stands for Simple Object Access Protocol and defines messaging protocol for communication. WSDL stands for Web Services Description Language and describes web service’s capabilities and how to access them.

Simple Object Access Protocol (SOAP)

It is a XML based network protocol that is used for exchanging structured data between nodes. It operates over application layer protocols such as HTTP and SMTP for formatting and transmitting messages. It makes sure that messages are are platform-independent and readable by different systems.

Architecture of SOAP Message

It has 4 layers present in its architecture :

• Envelope: Wraps the entire message.
• Header (optional): Contains information like authentication.
• Body: Holds the actual data or request.
• Fault (optional): Provides error handling information.

Example

Let's consider a sample SOAP message,

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"

xmlns:gfg="http://www.geeksforgeeks.org/webservice">

<soapenv:Header>

<gfg:AuthToken>ABC123XYZ</gfg:AuthToken>

</soapenv:Header>

<soapenv:Body>

<gfg:GetArticleDetails>

<gfg:ArticleID>12345</gfg:ArticleID>

</gfg:GetArticleDetails>

</soapenv:Body>

</soapenv:Envelope>

When a client wants to get article details from the GeeksforGeeks web service, it sends a SOAP message containing the request inside the Body (e.g., ArticleID) and an AuthToken inside the Header. The server checks the token for authentication, processes the request, and sends back a SOAP response with the requested article details in the response Body.

Characteristics of SOAP

It is more supportive than WSDL as it has three important characteristics which are,

• Independence: SOAP can work across different operating systems and programming languages.
• Neutrality: It can use various transport protocols like HTTP, SMTP, or TCP.
• Extensibility: SOAP allows additional features (like security or transactions) to be added via headers without breaking existing functionality.

Read more about Simple Object Access Protocol (SOAP).

Web Services Description Language (WSDL)

It was developed together by IBM and Microsoft and identified on June 26, 2007 by the W3C. It is XML based interface definition language that is used in describing the web service functionalities. Generally, a typical WSDL defines the implementation and communication process with XML based services. 

Architecture of WSDL Document

It has four main elements present in its architecture :

• <types> : Specifies the data types (using XML Schema) that the web service will use.
• <message> : Describes the individual pieces of data exchanged in each operation.
• <portType> : Lists the available operations and the messages they use for input and output.
• <binding> : Indicates the communication protocol and message format associated with each operation

Example

Given below is a simple example for understanding how messages and operations are defined in WSDL

<message name="simpleRequest">

<part name="input" type="xs:string"/>

</message>

<message name="simpleResponse">

<part name="output" type="xs:string"/>

</message>

<portType name="SimpleService">

<operation name="getResult">

<input message="simpleRequest"/>

<output message="simpleResponse"/>

</operation>

</portType>

Here,

• simpleRequest: The input message with one string parameter.
• simpleResponse: The output message with one string result.
• SimpleService: The service interface.
• getResult: The operation being performed (e.g., a lookup or calculation).

Read more about Web Services Description Language (WSDL).

Difference between SOAP and WSDL