Database Management System
Q82.
Consider the following relational schema:Student(school-id,sch-roll-no,sname,saddress) School(school-id,sch-name,sch-address,sch-phone) Enrolment(school-id,sch-roll-no,erollno,examname) ExamResult(erollno,examname,marks) Consider the following tuple relational calculus query. \begin{array}{l} \{t \mid \exists E \in \text { Enrolment } t=E \text { .school-id } \\ \wedge \mid\{x \mid x \in \text { Enrolment } \wedge x . \text { school-id }=t \wedge(\exists B \in \text { ExamResult } B . \text { erollno }=x . \text { erollno } \wedge B \\ \text { examname }=x . \text { examname } \wedge B . \text { marks }>35)\}|\div|\{x \mid x \in \text { Enrolment } \wedge x . \text { school-id }=t\} \mid \\ * 100>35\} \end{array}If a student needs to score more than 35 marks to pass an exam, what does the query return?Q83.
The following functional dependencies hold for relations R(A, B, C) and S(B, D, E) B \rightarrowA, A \rightarrowC The relation R contains 200tuples and the relation S contains 100tuples. What is the maximum number of tuples possible in the natural join R\Join S?Q84.
Consider the following relation schemas : b-Schema = (b-name, b-city, assets) a-Schema = (a-num, b-name, bal) d-Schema = (c-name, a-number) Let branch, account and depositor be respectively instances of the above schemas. Assume that account and depositor relations are much bigger than the branch relation. Consider the following query: \Pi _{c-name}(\sigma _{b-city="Agra" \wedge bal \lt 0} (branch \Join (account \Join depositor))) Which one of the following queries is the most efficient version of the above query ?Q85.
Information about a collection of students is given by the relation studinfo(\underline{studId}, name, sex). The relation enroll(\underline{studId}, courseId) gives which student has enrolled for (or taken) what course(s). Assume that every course is taken by at least one male and at least one female student. What does the following relational algebra expression represent?Q87.
Let r be a relation instance with schema R = (A, B, C, D). We define r_{1}=\Pi _{A,B,C}(R) and r_{2}=\Pi _{A,D}(R). Let s=r_1*r_2 where * denotes natural join. Given that the decomposition of r into r_1 and r_2 is lossy, which one of the following is TRUE?Q88.
Suppose the adjacency relation of vertices in a graph is represented in a table Adj(X,Y). Which of the following queries cannot be expressed by a relational algebra expression of constant length ?Q89.
Which of the following query transformations (i.e., replacing the l.h.s. expression by the r.h.s expression) is incorrect? R_1 and R_2 are relations, C_1 and C_2 are selection conditions and A_1 and A_1 are attributes of R_1.Q90.
Given the relations employee (name, salary, dept-no), and department (dept-no, dept-name,address), Which of the following queries cannot be expressed using the basic relational algebra operations \left(\sigma, \pi,\times ,\Join, \cup, \cap,-\right)?