creating a query using relational calculus (tuple relational calculus)

Question

I have the following database scheme:

student: sid
course: pid
prerequisite: cid, precid
records: sid, cid

How do I go about creating a query in relational calculus such that i need to find all courses for which all its prerequisites have been taken by every student who has taken the course PSY100? I want to write this with at least one universal quantification ?.

My idea was to find courses for which, for all courses to return, and for all students in records, there exist a student who took PSY100, that has also taken the prerequisite of that course to return.

so i have it written like this

{x:cid | ? c IN course [c(cid) = x(cid) AND
  ? y IN course ? r record
  ( y(cid) = c(cid) AND r(cid) = c(cid)
   → ? p IN prerequisite ( r(cid) = PSY100 AND r(cid) = p(pid) )] 

I am really confused about this. I am pretty sure this is wrong. any help would be greatly appreciated!

question from:https://stackoverflow.com/questions/65931324/creating-a-query-using-relational-calculus-tuple-relational-calculus

Answer 1

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