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

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

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

See similar textbooks

Similar questions

Show that the following decomposition of the schema R of Exercise 7.1 is not alossless decomposition:(A, B, C)(C, D, E).Hint: Give an example of a relation r(R) such that ΠA, B, C (r) ⋈ ΠC, D, E (r) ≠ r
Consider a relation schema R(A, B, C, D, E, G) and a set of functional dependencies F = {A → C, AD → CE, B → ACD, C → B}. (a) Show the steps of computing a canonical cover for F. (b) Compute the closure of AG and then determine whether or not AG is a candidate key. (c) Determine whether or not (A, E, G) is in BCNF and justify your answer using the transitive closure of a set of attributes. If (A, E, G) is not in BCNF, find a BCNF decomposition of it. (d) Assume that (A, E, G) is decomposed into (A, G) and (E, G). Given the above functional dependencies, is this decomposition always lossless? If so, prove this. Otherwise, explain it using an example (i.e., a case of decomposing a table containg rows and columns into two tables). (e) Assume that R is decomposed into R1(A, B, C, D) and R2(A, E, G). Is this decomposition dependency preserving? Justify your answer.
6.a. Draw dependency graphs corresponding to each grammarrule of Example 6.14(page 283) and for expression 7/4/3.0 6.b. Describe the two passes needed to compute the attributes onthe syntax tree of 7/4/3.0, including a possible order in which thenodes could be visited and the attribute values computed at eachpoint. and 6.14(page 283) is in the photo
The relation R defined on ℝ where aRb if and only if a< b is an equivalence relation. True or False
2) A relation schema R is defined tot be in 2NF if every nonprime attribute of R is blank the primary key of R.A) transitively dependent on B) fully functionally dependent onC) a candidate key of D) partially functionally dependent onE) part of
Consider a relation schema R = {A, B, C, D, E, G} and its functional dependency set F = {A → BCD,BC →DE,B → D,D → A}. Compute B+and choose the answer.(a) B+= AB(b) B+= ABC(c) B+= ABCD(d) B+= ABCDE(e) none of the above
Is it true that associative entities are likewise considered to be weak entities? What is your reasoning or lack thereof? If so, what distinguishes their "weakness" from others?
Consider a relation schema R = {A, B, C, D, E} and its functional dependency set F = {A → BC,CD → E,B →D,E → A}. Let R be decomposed into R1 and R2, where R1 = (A,B,C) and R2 = (A,D,E). Is the decompositionlossless? Is the decomposition dependency preserving? (a) The decomposition is lossless and dependency preserving.(b) The decomposition is neither lossless nor dependency preserving.(c) The decomposition is not lossless but dependency preserving.(d) The decomposition is lossless but not dependency preserving.
Our discussion of lossless decomposition implicitly assumed that attributes on the left-hand side of a functional dependency cannot take on null values. What could go wrong on decomposition, if this property is violated?
Consider a relation schema R = {A, B, C, D, E} and its functional dependency set F = {A → B,CD → E,B →D,E → A}. Compute A+ and choose the answer.(a) A+ = AB(b) A+ = ABC(c) A+ = ABCD(d) A+= ABCDE(e) none of the above
1. What technique is used to model the situation that Student may have multiple addresses? A) Associative Entity (gerund)B) Weak entitiesC) Super/sub typesD) Recursive relationships 2.There is m:m relationship between students and classes. Which technique is used forrepresenting the student grade? A) Associative Entity (gerund)B) Weak entitiesC) Super/sub typesD) Recursive relationships 3. An associative Entity (gerund) may be used whenever there are data that depends on twoentities even when their relationship is 1:m. True or FalseA) TrueB) False 4. (check all that apply) When do you use recursive relationships?A) the relationship between employees and their supervisorsB) the relationship between employees and their dependentsC) the relationship between employees and their departmentsD) the relationship between employees and their team membersE) the relationship between employees and their job assignments 5. How is a gerund converted into a relational model?A) ignore the gerund in the…
Can relationship exist if cardinality is reduced to zero. Provide reason and Explain with the help of example