--- title: "Web services architecture; SOAP and WSDL roles" subject: "Web Technology" chapter: 8 key: "semester_7/web_technology:web-services-soap-wsdl" source: https://www.bctengineer.com/q/semester_7/web_technology/web-services-soap-wsdl site: BCT Engineering --- # Web services architecture; SOAP and WSDL roles Web Technology · Chapter 8: Web services - Asked in: 2068 Chaitra (old course), 7 marks - Video: [API Web Services Beginner Tutorial 3 - What is WSDL and UDDI](https://www.youtube.com/watch?v=MUq_RkG7De0) — Automation Step by Step - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/web_technology/web-services-soap-wsdl - Whole chapter: https://www.bctengineer.com/md/semester_7/web_technology/chapter-8 ## Question Explain the Web services architecture. What are the roles of SOAP and WSDL? ## 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. ## Answer #### 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. ```text +--------------------+ | 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*. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which are the three roles in web services architecture? A. Client, server, proxy B. Service provider, service registry, service requester C. Sender, router, receiver D. Producer, broker, subscriber Answer: B. Provider creates and publishes, registry lists, requester finds and calls. (Key point: Three roles) 2. What are the operations of the architecture in order? A. Find, publish, bind B. Bind, find, publish C. Publish, find, bind/invoke D. Publish, bind, find Answer: C. The provider publishes, the requester finds, then binds and invokes. (Key point: Order of operations) 3. What is the role of WSDL? A. It carries the actual request and response B. It is an XML description of the service's operations, message formats, binding and endpoint C. It transports messages over the network D. It encrypts messages Answer: B. WSDL tells a requester what the service offers and how to call it; tools can generate client code from it. (Key point: Role of WSDL) 4. What is the role of SOAP in this architecture? A. Registry for finding services B. Description of service operations C. The messaging protocol defining the XML envelope for requests and responses D. A database for storing results Answer: C. SOAP is the message actually sent, carrying method name, parameters and result or Fault. (Key point: Role of SOAP) ## Related in Web Technology - [Web architecture and web-tier components](https://www.bctengineer.com/question.md?key=semester_7%2Fweb_technology%3Aweb-architecture-tiers) — Web Technology, chapter 2 - [XML document, XSLT and WSDL](https://www.bctengineer.com/question.md?key=semester_7%2Fweb_technology%3Axml-xslt-wsdl) — Web Technology, chapter 7 - [Short note: SOAP](https://www.bctengineer.com/question.md?key=semester_7%2Fweb_technology%3Ashort-note-soap) — Web Technology, chapter 8 - [Short note: SOA and SOAP](https://www.bctengineer.com/question.md?key=semester_7%2Fweb_technology%3Ashort-note-soa-soap) — Web Technology, chapter 8 - [Server side languages and multi-tier architecture](https://www.bctengineer.com/question.md?key=semester_7%2Fweb_technology%3Aserver-side-languages-multitier) — Web Technology, chapter 3 - [CMS and MVC architecture](https://www.bctengineer.com/question.md?key=semester_7%2Fweb_technology%3Acms-and-mvc) — Web Technology, chapter 5 ## Related in other subjects - [ISDN architecture, services and channels](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aisdn-architecture-channels) — Telecommunications, chapter 8, asked 2× - [Basic ISDN services and architecture](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aisdn-services-architecture) — Telecommunications, chapter 8 - [Web log mining and WWW mining architecture](https://www.bctengineer.com/question.md?key=semester_7%2Fdata_mining%3Aweb-log-mining-architecture) — Data Mining, chapter 7 - [Stateful vs stateless; NFS architecture](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Anfs-stateful-stateless) — Distributed System, chapter 2