Disco: The Discovery (or Disco) protocol helps developers automatically determine what services and features are provided in a Web service. It defines both a discovery format based on XML and a protocol for retrieving that discovery document. The thing to remember is that Disco has to have a known URL to search for services.
SOAP: The Simple Object Access Protocol (SOAP) is basically there for information exchange. Its specs define an extensible message format and binds to the HTTP protocol.
WSDL: Web Services Description Language (WSDL) is an extensible service description language that is often used. It’s really an XML-based contract language.
UDDI: Universal Description, Discovery, and Integration (UDDI) was created specifically as a way to discover service providers, without knowing the URL.