Apologies, I meant LSA (Light Sports Aircraft).
There used to be a category called SLA (Small Light Aeroplane) but it got merged into microlight. I could explain that history, but I suspect that nobody's deeply interested.
SSDR is, again, an airworthiness, not a licencing category. It stands for "Single Seat, DeRegulated" and now co-incides with the single seat microlight definition. It has nothing to do with licencing, which is the same as for any other microlight.
G