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Web services architecture; SOAP and WSDL roles

Short answer

Web services architecture has three roles: service provider publishes a WSDL description to a registry (UDDI), service requester finds it and binds via SOAP/HTTP. WSDL describes operations and message formats; SOAP is the XML messaging protocol that carries requests and responses.

Explain the Web services architecture. What are the roles of SOAP and WSDL?

Web service

A web service is a software component that provides functionality over the network using standard Internet protocols, so that applications written in different languages and running on different platforms can interact. Data is exchanged in XML (or JSON).

Web services architecture

It follows the service-oriented model, with three roles and three operations.

              +--------------------+
              |  Service registry  |
              |       (UDDI)       |
              +--------------------+
               ^                  ^
       2. find |                  | 1. publish (WSDL)
               |                  |
     +-----------+            +-----------+
     |  Service  |  3. bind / |  Service  |
     | requester |<---------->| provider  |
     +-----------+ SOAP / HTTP+-----------+
  • Service provider: Creates the service, describes it in WSDL, and publishes it.
  • Service registry (broker): A directory (UDDI) in which providers publish services and requesters search for them.
  • Service requester (consumer): Finds the service in the registry, reads its WSDL, and calls it.
  • Operations: publish, find, bind/invoke.

Technology stack: HTTP/SMTP (transport), SOAP (messaging), WSDL (description), UDDI (discovery), all based on XML.

Role of SOAP

SOAP is the messaging protocol. It defines the XML envelope (Header + Body) in which requests and responses travel, usually over HTTP. It carries the method name and parameters from the requester, and the result (or a Fault) back from the provider, in a platform- and language-independent way.

Role of WSDL

WSDL is an XML document that describes the service: the operations it offers, the input/output message formats and data types, the protocol binding (e.g. SOAP/HTTP) and the endpoint URL. A requester reads the WSDL to learn how to build correct SOAP messages, and tools can generate client code from it.

In short, WSDL says what the service offers and how to call it, and SOAP is the message actually sent.

✓ Answer checked by Claude Opus 5.5 (high effort)

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