Web services allow applications to expose functions and messages over the web using open standards like XML, SOAP, and HTTP. There are two main types: SOAP and RESTful web services. Web services provide interoperability between different applications and low-cost communication through standardized protocols. The web service architecture involves service providers that implement and publish services, service requestors that consume existing services, and service registries that provide a central directory. Key components of the architecture include transport layers, XML messaging, service descriptions using WSDL, and service discovery using UDDI.