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DBMS Chap 3

Here are the key points about representing weak entity sets in an ER diagram: - A weak entity set is dependent on a strong/parent entity set. It cannot exist without an instance of the parent entity set. - A weak entity set is represented by placing its name inside a double rectangle in the ER diagram. - A double diamond symbol is drawn from the weak entity set to the parent entity set to represent the many-to-one relationship between them. - Attributes that form the primary key of the weak entity set are underlined. These attributes must contain the primary key of the parent entity set to identify an instance of the weak entity set. So in summary, the double diamond symbol is used to

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101 views5 pages

DBMS Chap 3

Here are the key points about representing weak entity sets in an ER diagram: - A weak entity set is dependent on a strong/parent entity set. It cannot exist without an instance of the parent entity set. - A weak entity set is represented by placing its name inside a double rectangle in the ER diagram. - A double diamond symbol is drawn from the weak entity set to the parent entity set to represent the many-to-one relationship between them. - Attributes that form the primary key of the weak entity set are underlined. These attributes must contain the primary key of the parent entity set to identify an instance of the weak entity set. So in summary, the double diamond symbol is used to

Uploaded by

Harsh Ojha
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Exercise normalization

The following table is already in first normal form (1NF). There is only one entry per field. Please convert this table to
the third normal form (3NF) using the techniques you learned in this Unit. Write a short report about your solution and
post it in the discussion board. Check the other solutions and comment them, if necessary. If you have questions, you
can also post them in the discussion board. A tutor will look at the questions regularly and give feedback and answers.

A table with the students and their grades in different topics.

UnitID StudentID Date TutorID Topic Room Grade Book TutEmail

U1 St1 23.02.03 Tut1 GMT 629 4.7 Deumlich tut1@fhbb.ch

U2 St1 18.11.02 Tut3 GIn 631 5.1 Zehnder tut3@fhbb.ch

PU1 St4 23.02.03 Tut1 GMT 629 4.3 Deumlich tut1@fhbb.ch

U5 St2 05.05.03 Tut3 PhF 632 4.9 Dümmlers tut3@fhbb.ch


UnitID StudentID Date TutorID Topic Room Grade Book TutEmail

U4 St2 04.07.03 Tut5 AVQ 621 5.0 SwissTopo tut5@fhbb.ch

Consider the relation scheme R = {E, F, G, H, I, J, K, L, M, M} and the set of functional


dependencies {{E, F} -> {G}, {F} -> {I, J}, {E, H} -> {K, L}, K -> {M}, L -> {N} on R. What is
the key for R?

Consider a relation scheme R = (A, B, C, D, E, H) on which the following functional


dependencies hold: {A–>B, BC–> D, E–>C, D–>A}. What are the candidate keys of R?

Consider the two tables below:


Student

StudentCourse
 INNER JOIN
 LEFT JOIN
 RIGHT JOIN
 FULL JOIN

1. Consider the following employees and departments tables from the sample
database:

 find all employees who locate in the location with the id 1700.
 finds the employees who have the highest salary:

 The following statement finds all employees who salaries are greater
than the average salary of all employees:

 finds all departments which have at least one employee with the salary
is greater than 10,000:
 finds all departments that do not have any employee with the salary
greater than 10,000:
 finds all employees whose salaries are greater than the lowest salary of
every department:

The following database diagram illustrates the HR sample database:


2. Which one of the following is used to represent the supporting many-
one relationships of a weak entity set in an entity-relationship diagram?

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