WSDL - WSDL, SOAP, and UDDI Overview

1. WSDL, SOAP, and UDDI Overview

They work together in a Service-Oriented Architecture (SOA):

• WSDL defines what the service does and how to use it.

• SOAP defines how messages are sent.

• UDDI helps find the service and retrieve its WSDL.

2. How WSDL, SOAP, and UDDI Work Together

The interaction follows the Publish → Discover → Bind model:

Step 1 — Publish (Provider → UDDI)

• The Service Provider creates a WSDL file.

• Publishes it to the UDDI registry for discovery.

• Example:

  Service: CustomerService
  WSDL: http://example.com/services/customer?wsdl
  Endpoint: http://example.com/services/customer
  

Step 2 — Discover (Consumer → UDDI)

• The Service Consumer queries the UDDI registry to find services.

• UDDI returns the WSDL URL and metadata.

Step 3 — Bind & Invoke (Consumer → Provider via SOAP)

• The Consumer downloads the WSDL.

• Uses it to generate client code using tools like:

  • Java → wsimport

  • .NET → svcutil

  • Python → zeep

• The consumer sends SOAP requests to the Service Provider.

• The provider sends back SOAP responses.

3. Example of WSDL + SOAP + UDDI

Scenario: Bank Account Service

• Provider: ABC Bank

• Consumer: XYZ Corp

• Registry: UDDI Directory

Step 1 — WSDL Created

ABC Bank creates a WSDL for AccountService:

<definitions name="AccountService"
  targetNamespace="http://abcbank.com/account"
  xmlns:tns="http://abcbank.com/account"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema"
  xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
  xmlns="http://schemas.xmlsoap.org/wsdl/">

  <message name="GetBalanceRequest">
    <part name="accountID" type="xsd:int"/>
  </message>
  <message name="GetBalanceResponse">
    <part name="balance" type="xsd:decimal"/>
  </message>

  <portType name="AccountPortType">
    <operation name="GetBalance">
      <input message="tns:GetBalanceRequest"/>
      <output message="tns:GetBalanceResponse"/>
    </operation>
  </portType>

  <binding name="AccountBinding" type="tns:AccountPortType">
    <soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http"/>
  </binding>

  <service name="AccountService">
    <port name="AccountPort" binding="tns:AccountBinding">
      <soap:address location="http://abcbank.com/services/account"/>
    </port>
  </service>
</definitions>

Step 2 — WSDL Published to UDDI

• ABC Bank registers the WSDL in the UDDI directory.

Step 3 — Consumer Discovers WSDL

• XYZ Corp queries UDDI:

  find_service("AccountService")
  

• UDDI returns:

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

Step 4 — Consumer Uses SOAP

XYZ Corp generates client code:

AccountService service = new AccountService();
AccountPort port = service.getAccountPort();
double balance = port.getBalance(101);
System.out.println(balance);

• Request: SOAP XML request sent to ABC Bank.

• Response: SOAP XML response with account balance.

4. WSDL + SOAP + UDDI Workflow

Architecture Steps:

1. Service Provider

   • Creates WSDL → Publishes to UDDI.

2. Service Registry (UDDI)

   • Stores and organizes WSDLs → Makes them searchable.

3. Service Consumer

   • Finds WSDL in UDDI → Generates client code → Calls service using SOAP.

5. Roles in SOA

6. Key Points

• WSDL → Defines the what and how of the service.

• SOAP → Handles communication between consumer and provider.

• UDDI → Helps discover available services.