18. Consider the relation schema CLASS with attributes Student, Subject, and Teacher. The meaning of this relation is that the specified student is taught the specified subject by the specified teacher. Assume that semantic rules, depicted by the following functional depen- dencies, exist: {Student, Subject} → Teacher Teacher → Subject Subject A Teacher {Student, Teacher} → Subject а. What do these rules mean in words? Are all these rules necessary? If not, explain which are not needed. b. Is the following sample data consistent with these rules? Why or why not? Student Subject Teacher Smith Math White Smith Physics Green Jones Math White Jones Physics Brown С. What causes CLASS to contain a BCNF violation? What anomalies does it exhibit? d. Decompose CLASS if necessary so that the resulting relational schema is in BCNF. Is your design attribute-preserving, dependency-preserving, and a lossless-join decompo- sition? Exnlain

Database System Concepts
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ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
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18. Consider the relation schema CLASS with attributes Student, Subject, and Teacher. The
meaning of this relation is that the specified student is taught the specified subject by the
specified teacher. Assume that semantic rules, depicted by the following functional depen-
dencies, exist:
{Student, Subject} → Teacher
Teacher → Subject
Subject A Teacher
{Student, Teacher} → Subject
a. What do these rules mean in words? Are all these rules necessary? If not, explain
which are not needed.
b. Is the following sample data consistent with these rules? Why or why not?
Student
Subject
Teacher
Smith
Math
White
Smith
Physics
Green
Jones
Math
White
Jones
Physics
Brown
С.
What causes CLASS to contain a BCNF violation? What anomalies does it exhibit?
d. Decompose CLASS if necessary so that the resulting relational schema is in BCNF. Is
your design attribute-preserving, dependency-preserving, and a lossless-join decompo-
sition? Explain.
Transcribed Image Text:18. Consider the relation schema CLASS with attributes Student, Subject, and Teacher. The meaning of this relation is that the specified student is taught the specified subject by the specified teacher. Assume that semantic rules, depicted by the following functional depen- dencies, exist: {Student, Subject} → Teacher Teacher → Subject Subject A Teacher {Student, Teacher} → Subject a. What do these rules mean in words? Are all these rules necessary? If not, explain which are not needed. b. Is the following sample data consistent with these rules? Why or why not? Student Subject Teacher Smith Math White Smith Physics Green Jones Math White Jones Physics Brown С. What causes CLASS to contain a BCNF violation? What anomalies does it exhibit? d. Decompose CLASS if necessary so that the resulting relational schema is in BCNF. Is your design attribute-preserving, dependency-preserving, and a lossless-join decompo- sition? Explain.
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