WSDL - SOAP is Called a Communication Protocol

1. What is SOAP?

SOAP stands for Simple Object Access Protocol.
It is a protocol used to exchange structured information between systems over a network.

• Type: Communication protocol

• Format: Uses XML to structure messages.

• Transport: Usually works over HTTP or HTTPS, but can also use SMTP, JMS, etc.

• Purpose: Allows different applications (built on different platforms or languages) to communicate with each other.

In simple terms:
SOAP = Rules for sending and receiving XML messages between systems.

2. Why SOAP is Called a Communication Protocol

SOAP provides standardized rules for communication between a service provider and a service consumer.

It defines:

• How to format the request and response messages.

• How to send messages over the network.

• How errors are handled.

• How the client and server interoperate, even if they use different programming languages.

For example:

• A Java service provider can communicate with a .NET or Python consumer using SOAP because both follow the same protocol rules.

3. SOAP and WSDL Relationship

• WSDL: Describes what the service does and how to call it.

• SOAP: Defines how to send the message according to the WSDL.

Example:

• WSDL defines:

  • Operation: getBalance(accountID)

  • Input: accountID

  • Output: balance

• SOAP defines the XML format for sending the request and receiving the response.

4. SOAP Message Structure

A SOAP message is always an XML document with a fixed structure.

SOAP Request Example

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
                  xmlns:acc="http://abcbank.com/account">
   <soapenv:Header/>
   <soapenv:Body>
      <acc:GetBalanceRequest>
         <acc:accountID>101</acc:accountID>
      </acc:GetBalanceRequest>
   </soapenv:Body>
</soapenv:Envelope>

SOAP Response Example

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
                  xmlns:acc="http://abcbank.com/account">
   <soapenv:Header/>
   <soapenv:Body>
      <acc:GetBalanceResponse>
         <acc:balance>2500.75</acc:balance>
      </acc:GetBalanceResponse>
   </soapenv:Body>
</soapenv:Envelope>

5. SOAP Message Components

6. How SOAP Works in Web Services

Step 1 — WSDL Defines the Contract

• The WSDL file tells the consumer:

  • Which operations are available.

  • What SOAP XML format to use.

  • Which endpoint URL to send the request to.

Step 2 — SOAP Sends the Request

• The service consumer generates a SOAP XML request based on WSDL.

• Sends it to the service provider via HTTP.

Step 3 — SOAP Receives the Response

• The provider processes the request.

• Sends a SOAP XML response back to the consumer.

7. Example Workflow

Scenario:

ABC Bank provides a GetBalance web service.

1. Consumer reads WSDL:

   http://abcbank.com/services/account?wsdl
   

2. Consumer generates SOAP request:

   <soap:Body>
     <GetBalanceRequest>
       <accountID>101</accountID>
     </GetBalanceRequest>
   </soap:Body>
   

3. Provider responds with SOAP:

   <soap:Body>
     <GetBalanceResponse>
       <balance>2500.75</balance>
     </GetBalanceResponse>
   </soap:Body>
   

8. SOAP Features

• Platform-independent → Works across Java, .NET, PHP, Python, etc.

• Language-neutral → Uses XML, so any programming language can read/write.

• Protocol-independent → Works over HTTP, HTTPS, SMTP, JMS, etc.

• Extensible → Supports security, authentication, and transactions.

• Strict → Strongly typed and follows WSDL definitions exactly.

9. SOAP vs REST (Quick Comparison)

10. Summary

• SOAP is a communication protocol for exchanging XML-based messages.

• It works with WSDL to define the structure of requests and responses.

• It often integrates with UDDI for service discovery.

• It ensures platform-independent and language-neutral communication.