Is it possible to publish a synchronous web service from Appian? The

The Call Web Service Smart Service allows you to integrate data from web services within your process and automatically create a custom data type with it.
Checkout:
forum.appian.com/.../Call_Web_Service_Smart_Service

You can use the Call Web Service SS to call a web service and fetch values in return.
You may test the smart service using one of the freely available web services from the following link:
www.webservicex.net/.../WSDetails.aspx
Invoking the above webservice will automatically create data types(forum.appian.com/.../Call_Web_Service_Smart_Service for you which you can use to store values.

Thanks for the answer guys however you're both talking about consuming an external service whereas I'm interested in creating a webservice for others to use.

It is not possible to return any values as this triggers a process that doe possibly run for weeks until completed. So you can start a process via WS from another system. To return any data you need a seperate path like a DB or a WS callback to the other system.

Thanks Stefanh - that's what I'd assumed as well but I wanted to be sure. Looks like asynchronous service calls only.