Facebook Connect API : Data.defineAssociation - How to use it?

Question

Hello, Im using the Facebook Data Api and I want to create a Association. For this I have to use Data.defineAssociation and I want to know, how to set the parameters into a NSDictionary. Im using the Facebook iPhone Sdk:

NSDictionary *params = [NSDictionary dictionaryWithObjectsAndKeys:
// parameters ???
, nil];
[[FBRequest requestWithDelegate:self] call:@"facebook.data.defineAssociation" params:params];

I want to define a Association between the user_id and the object_id;

Here is an example (xml):

// I know how to write the first line with the iPhone SDK
$objectID = $facebook->api_client->data_createObject("foo", array("foo" => "$foo") );
$facebook->api_client->data_defineAssociation( "user_to_row", 1, array("alias" => "user_id"), array("alias" => "row_id") );

I looked on the documentation http://wiki.developers.facebook.com/index.php/Data.defineAssociation and it says that the parameter should be a complex. How can I set this parameter?

Thanks for the help!