Database Structures Homework Refer: Database System Concepts, 6th edtion for thi

Question

Database Structures Homework

Refer: Database System Concepts, 6th edtion for this assignment.

Consider the E-R diagram for the university database as given on page 282 of the text book. Answer the following questions

[5 points] Name one weak entity set.

[5 points] Name one recursive relationship set.

[5 points] What does the double line that joins the entity set instructor with the relationship set inst_dep indicate?

[5 points] What does the double-lined diamond shape around the relationship set sec_course indicate?

[30 points] Translate the lower part of the University E-R diagram, which is shown below into a relational database (i.e., translate this part of the E-R diagram into relational schemas.)

Explanation / Answer

1.)   A weak entity is the entity which can't be fully identified by its own attributes and takes the foreign key as an attribute (generally it takes the primary key of the entity it is related to) in conjunction.

Examples

The existence of rooms is entirely depended on the existence of a hotel. So room can be seen as the weak entity of the hotel. Also the room category of the room is also the weak entity.

A week entity set in ER diagram is represented by double outline rectangle.

In the above ER diagram there is no Such rectangle i.e there is no any week entity. But there is a week relationship between section and course(Sec_Course is a week relationship)

2.) A relation is Recursive relation when it participates more than one time in the realtionship. Like supervisor and employee relation. Employee can be supervisor and can be supervised also by a employee.

PreReq is a Recursive relation in the above ER diagram. Course may have prereqs and vice versa.

3.) In a ER diagram double line coming from an entity indicates Total participation of that Entity in the relationship. The Instructor Entity is fully participating in the relationship Instr-dept.that means Instructor must have a dept in the relationship Inst-dept.

4. ) As described in the ans1 , it represents a week relationship. To identify a week relationship keep two things in mind---------

Here section is child entity and doesn't contains Pk of its parent Course. and Both tables are independent.

5.)   

Entity is existence-independent of other enties

PK of Child doesn’t contain PK component of Parent Entity

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