Wsdl
WSDL is a markup language that describes a web service. To use this web service, client application developers need to know the methods provided by the web service and the parameters that must be passed to these methods. It is imperative that access to these methodologies is available at design time, and it is this need that is associated with WSDL.
DISCO
The Web Service Discovery Tool ( DISCO ) is used to discover the URLs of XML web services located on a web server and stores documents associated with each XML service on a local drive. DISCO takes the URL and detects and publishes documents for discovery (.wsdl, .xsd, .disco, and .dicomap files) as arguments. Some of the features available for use with this tool are:
/ d [omain]: domain - specifies the domain name that will be used when connecting to a proxy server that requires authentication
/ nosave - does not save the detected document or results
/ nologo - Suppresses Microsoft startup banner display
/ o [ut]: directoryName - specifies the output directory in which to save the detected documents. The current directory is the default.
/ p [assword]: password - specifies the password to use when connecting to the proxy server
/ proxy: url - Specifies the URL of the proxy server that will be used for HTTP requests.
DISCO is a tool, not a web service.
EVENT
if you mean WS-Eventing, see here .