The next step is to identify the responsibilities of the domain objects. At this stage, it can also be helpful to use "computer-free" techniques such as CRC cards to identify responsibilities, entering the results as new responsibility elements. (CRC cards--"Class-Responsibility-Collaboration" cards--are a technique developed by Ward Cunningham and Kent Beck using index cards to represent candidate objects in a system and elucidate their collaborations.)
To find responsibilities, go through the text of a use case and identify what the things and actors must do. You can then assign each responsibility to the appropriate thing or actor. In addition, each responsibility can be linked to collaborating participants, the other things or actors that participate in the responsibility.