Dialogs can store additional parameters. These parameters can be used to store an additional data. Also these parameters can be used in dialogs retrieval requests.
To start use additional parameters it needs to create an additional schema of your parameters. This is a CustomObjects class. Just create an empty class with all needed fields. These fields will be your dialog additional parameters.
Next, to set additional parameters to a dialog use next additional parameters in a creation request:
data[class_name] - should contain CustomObjects class name created above
data[field1]
data[...]
data[fieldN]