In Amazon Mechanical Turk, when creating an External Question then it will send you each assignment like this:
http://tictactoe.amazon.com/gamesurvey.cgi?gameid=01523
&hitId=123RVWYBAZW00EXAMPLE
&assignmentId=123RVWYBAZW00EXAMPLE456RVWYBAZW00EXAMPLE
Surprisingly, it doesn't send me the workerId and I can't find any way to do this. The closest method is GetAssignmentsForHIT which only gives me the assignment already submitted but I need to render the assignment based on the worker history.
A recent addition to the API is the GetAssignment call, which takes the assignment ID as an argument and will return the Worker ID inside the Assignment data structure.
As msha points out, the sending of a workerID parameter to an ExternalQuestion page seems to be deprecated, or at least taken out of the latest version of the documentation.
However, a fellow researcher who's been using MTurk a lot says: "People seem to be using it in the forums. I would go ahead with it...if it ever actually disappears, I'm sure that the developer community will yell very loudly. :) "
I tried it empirically today (2011-08-19), and indeed a workerID is being sent to the ExternalQuestion page I set up on my own server, after the HIT has been accepted. This was in the sandbox. My ExternalQuestion page contained a Java Web Start button (as described here: http://download.oracle.com/javase/tutorial/deployment/deploymentInDepth/createWebStartLaunchButtonFunction.html ); I don't know if that made any difference.
According to the MTurk docs here,
When a Worker accepts your HIT, you can get the ID of the Worker. If your HIT contains a Java Applet, an IFrame, or embedded binary data, the URL contains a value for the workerId. If your HIT does not contain these types of data, or if a Worker has not accepted the HIT, the workerId element doesn't appear.
Haven't tried to confirm this myself yet.
