hi everyone...i'm a newbie and this is my first database design. i'm trying to create a database that holds information for different sporting entities/bodies/associations. an entity can be one of three distinct types: NSA, SRE or SP. each entity has the basic information such as name, address etc...a sporting entity, (according to its type), can have members (these members can be thought of as an executive) and the sport entity can control various sports clubs...for example an Athletic Association (sport entity) can control athletic club A, athletic club B, etc.

now the challenge that i'm facing is that each sport entity can only be of a certain type (NSA, SRE or SP) and this type determines various characteristics. So if i put a type column in the sport entity table, i would have to put all the attributes that are related to each type and this of course will generate a lot of nulls depending on the type selected.

i have the following tables:

1) sportentity(se_id(pk), se_name, se_address)

2) sportentity_NSA/SRE(NSA/SRE_id(pk), se_id(pk), date_established, designation)

3) sportentity_SP(sp_id(pk), se_id(pk), period_of_service)

4) members(mem_id(pk), se_id(fk), mem_firstname, mem_lastname, mem_position)

5) club(club_id(pk), se_id(fk), club_name)

based on the above info:

1) are my tables made up correctly?
2) if so, how do i implement the relationships?
3) if not, how should i re-structure my design?