That said, you can approximate an IS-A relationship between tables, but it's cumbersome and prone to mistakes.

This statement seems contradictory to your idea about a separate table for optional attributes. That is merely a further generalization of the approximate IS-A relationship, and is equally cumbersome and prone to mistakes, if not moreso.

How is it more cumbersome to have the tables 

Animal
  .id
  .name
  .type

Mammal
  .animal_id
  .hair_color

Reptile
  .animal_id
  .num_of_limbs

[download]

Than to have the tables you are proposing? 

Animal
  .id
  .name
  .type

AnimalAttribute
  .animal_id
  .attribute_id
  .value

Attribute
  .id
  .name

[download]

--Solo
--
You said you wanted to be around when I made a mistake; well, this could be it, sweetheart.

In reply to Re^3: OO concepts and relational databases by Solo
in thread OO concepts and relational databases by dragonchild

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