Spot the relational concept that does NOT belong

Exercise and reference answers

Questions

1. Items

   1. Primary key
   2. Object key
   3. Foreign key
   4. Candidate key

   Reason

   'Object key' is not a relational-model concept; the others are.

   Odd item

   Object key

2. Items

   1. Projection
   2. Selection
   3. Polymorphism
   4. Join

   Reason

   Polymorphism is an OO concept; the others are relational algebra operations.

   Odd item

   Polymorphism