Question

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In DBMS, what would you use to obtain information about the current logical structure of the database? How this information is recorded in the DBMS and who is responsible to maintain it?

Question Two

Consider the following schema:

Student(id, name)

Registration(id, code)

Course(code, instructor)

1. Explain how we can violate the foreign key constraint from the id attribute of Registration to the Student relation.
2. Give the following queries in the relational algebra.

       1-What are the names of students registered in IT244?            

2-What are the names of students registered in both IT244 and CS141

3-What are the names of students who are taking a subject not taught by Philips?

3. For each of the following relational algebra queries, write in English what they mean.

1. Π_instructor (σ_{code=IT446 or code=IT230}(Course))                 

2. Π_name (σ_code=IT446 (Student ⋈ Registration)) ⊔ Π_name (σ_code=IT441(Student ⋈ Registration))

Answer 1

If you have any doubts, please give me comment..

A)

Let me take Student table have some ids i.e 101, 102, 103, 104. Then if we want to insert tuples into Register table other than which are existed in Student table. Suppose if we want to insert Student registration of 105, then it violates the foreign key constraint, because student id 105 doesn't exists in Student.

B)

1)

2)

3)

C)

1) Find the name of instructors, who teach course code IT446 or IT230.

2) Find the name of the students, who registered subjects IT446 or IT441