Let R(D,E,F) be a relational schema. determine for each of the following equalit

Question

Let R(D,E,F) be a relational schema. determine for each of the following equalities whether both sides have the same result. Justify the reply. Consider the following relational schema; the schema describes a database containing data about theses carried out by students of a master degree. Theses have supervisors and co-supervisors. The underlined attributes denote the primary keys of the relations. determine for each relation, the foreign keys. Based on the primary and foreign keys of the relations, answer the following questions (justify your answers): Can a professor supervise more than one thesis? Can a thesis have multiple supervisors? Can a thesis have multiple co-supervisors? Consider the relational schema in question (2) above. Discuss if and when Pi_rate These = Pi_rate (Theses Theses-Co-Supervisors) Express the following queries in relational algebra determine the topic of the thesis by student Bob Rossi. determine the name of the co-supervisor(s) of the thesis by student Bob Rossi. determine if there is any professor that has supervised no thesis.

Explanation / Answer

1.

i. both side are equal

when F=7 not exists between 10 and 15 of D value

if F=7 value exists for rows coresponding for D > 15 only the sides are equals

ii. both sides are equal

when F=7 for all corresponding D values between 10 and 15

  

2.

a.

forign key of each relation in the relatioanl shema:

students forign key is S#

thesis T#

professors prof#

thesis co-super visor T# and Prof#

2.

b. can a professor suerise more than one thesis :yes

explanation:

in relation thesis each thesis T# the professor prof# may be any one for different T# same prof# may exist , there is no restriction on that.

can a thesis have multiple supervisors : no

expalnation:

each T# in thesis only one value prof# will exist no multple values in prof# entry.

an a thesis have multiple co- supervisors : no

expalnation:

each T# in co-suervisor only one value prof# will exist no multple values in prof# entry.

3. this is query when no co-supervisor exist for a particular thesis, natural join of thesis and thesis-co-supervisor gives details of table that includes

X <T#,title,topic,prof#,s#,evaluation>, say X

among the above details from the column titles ,the above query extracts title which are not there in X, then it gives title those who dont have co-supervisors.

  

4.

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