Database-Relational Algebra

Question

Given the following relations

Vehicle(reg_no,make,colour)

Person(eno,name,address)

Owner(eno,reg_no)

List the names of persons who own only Maruti Cars.

 

So, in person relation there may be three types of people

(1)Person who don’t own any car

(2)Person Who own only Mutiple cars of different make.

(3)Persons who own only Maruti Cars.

So, I have to select only 3^rd Type of person from person relation.

I do following set of computations

(1)$T_1\leftarrow \pi _{eno}(vehicle \bowtie_{make \neq Maruti} Owner)$ // Now T1 contains all eno of person who own a non-Maruti car.

(2)$T_2 \leftarrow \pi_{eno}(Owner)-T_1$ //Now T2 will contain eno of all those people who own only Maruti Car

(3)$\pi_{name}(Person \bowtie T_2)$ //Now this shall give me names of persons who own only Maruti Cars.

Am I correct?

 

Comments

Yes I think it is correct..

Answer 1

$\pi_{\text{name}} $ (  $\sigma_{\text{make}=maruti}$ ( vehicle $\bowtie$ person $\bowtie$ owner )) – $\pi_{\text{name}} $ (  $\sigma_{\text{make} \neq maruti}$ ( vehicle $\bowtie$ person $\bowtie$ owner )) this is correct

$\pi_{\text{name}} $ (  $\sigma_{\text{make}=maruti}$ ( vehicle $\bowtie$ person $\bowtie$ owner )) this is not correct