Proposed solution for WS-I Web Services:

The default solution for asynchronous services in the WS stack is to use [attachment:ticket:1:True-Asynchronous-Model-from-Gent.png callback operations]. In the bioinformatics domain we can not assume that  client would have the possibility to expose an external service interface, this does not seem like a viable solution for now.    

[attachment:ticket:1:Polling-Asynchronous-Model-from-Gent.png A solution based on polling] is more light-weight since it does not assume that a client exposes a service interface. 
As there are no available standards for such an interface, we are free to define one. One solution is to use the soaplab async. interface.
This is [http://soaplab.sourceforge.net/soaplab1/images/soaplab-api.jpg described in the soaplab documentation], but would be useful if it were defined in a wsdl file, which could then be imported into the wsdl of the service you wish to provide a asyc interface to.