How to find all pizzerias that serve every pizza eaten by people over 30?

Question

I\'m following the Stanford Database course and there\'s a question where we have Find all pizzerias that serve every pizza eaten by people over 30 using Re

Answer 1

1. On slide 6, note that n is (3 1 7).

2. On the next slide, o / n results in (4 8).

3. If o would also have (12 3) and (12 1) but not (12 7), 12 would not be part of o / n.

You should be able to fill in an example in the formula on Slide 16 and work it out.

1. In your case, we take ɑ to be:

   Chicago Pizza   cheese  cheese
   Chicago Pizza   cheese  supreme
   Chicago Pizza   supreme cheese
   Chicago Pizza   supreme supreme
   Dominos         cheese  cheese
   Dominos         cheese  supreme
   

2. Then we take β to be:

   cheese cheese
   cheese supreme
   supreme cheese
   supreme supreme
   

3. The result of ɑ / β would then be:

   Chicago Pizza
   

Dominos is not part of this because it misses (supreme cheese) and (supreme supreme).