For personal educational purposes I am making a site for a conference. One of the object that exist in a conference is a session, which has different states and in each state it has slightly different attributes:

1. When submitted it has a speaker (User in the system), Title and abstract.
2. When under review it has reviews and comments (in addition to the basic data)
3. When accepted it has a defined time-slot but no reviewers anymore.

I feel that it is not the best thing to add a "status" attributes and start adding many if statements...
So I thought it would be better to have different classes for each state each with it's own validations and behaviors.

What do you think about this design? Do you have a better idea?

*I must add this out of frustration: I had several edits of the question, including one major change but no one actually gave any hint or clue on which direction should i take or where is a better place to ask this... Hardly helpful.