First of all, I don't know much of web service. But is it possible to achieve the following?

I have a table which contains two columns, first column is "date", second column is some numeric measurement, say "A". I also have a web server set up which takes a date and a numeric value and returns  another value based on the given information.

So I should get three columns, the first two being "date" and "A", and the last one is returned by the web service. I then need to plot the third column against date.

Is this possible in Tableau using Web Service Connector? There is not much in the Help and based on my try, you need to specify the query at the datasource page which (to my understanding) eliminates the chance of the query taking one column as parameter.

Please help!