0

I've been reading the book "Database System Concepts Seventh Edition".

and the author says

A lower-level entity set (or subclass) also inherits participation in the relationship sets in which its higher-level entity (or superclass) participates.

does that also apply on a total participation constraint ?

for example, if the higher-level entity set has a total participation in a relationship "R"

then it also enforces each entity of the lower-level entities sets to participate in the relationship "R" ?

here is another example, suppose we have an entity set "Staff" and it has arbitrary subclasses "Doctor" and "Teacher".

Let's also assume that we have a separate entity set called "Building".

and we have a relationship set called "works_at".

the Building entity set has partial participation in relationship set "works_at"

and Staff entity set has a total participation in relationship set "works_at"

if Staff has total participation, then "Doctor" and "Teacher" also have total participations in "works_at" relationship ?

here is a diagram. enter image description here

AngryJohn
  • 576
  • 4
  • 10
  • a picture would help in this case – nbk Aug 20 '22 at 14:52
  • @nbk i've attached a diagram :) – AngryJohn Aug 20 '22 at 15:09
  • yes they have, as teachers and doctors are the staff, which is also true for all subclasses, they inherit it from its p0arent class – nbk Aug 20 '22 at 15:29
  • @nbk Thank you, and i have one last question, if add entity to the "Teacher" entity set will the entity "theoretically" also appear in the staff entity set ?(i just couldn't find an answer for that) – AngryJohn Aug 20 '22 at 17:27
  • if you add a relationship between teacher and staff, you don't have a subclass any more, so it doesn't inherit – nbk Aug 20 '22 at 17:31

0 Answers0