relational calculus

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relational calculus

spectra

SSCarpal Tunnel

Points: 4120
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October 21, 2018 at 9:33 pm

#381535

I'm solving a problem using tuple relational calculus ( TRC) in DBMS.
Problem
Find the name of all the employees who work for XYZ Bank Corporation.
Solution ( as given in my book)
I don't understand why book is using S . We have t . Since both of them represents tuples , we could just use t in place of S and get moving.
Can anyone please explain why we required S ?

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Jeff Moden SSC Guru Points: 1004403 More actions · Answer 1

spectra - Sunday, October 21, 2018 9:33 PM
I'm solving a problem using tuple relational calculus ( TRC) in DBMS.
Problem
Find the name of all the employees who work for XYZ Bank Corporation.
Solution ( as given in my book)
I don't understand why book is using S . We have t . Since both of them represents tuples , we could just use t in place of S and get moving.
Can anyone please explain why we required S ?

Are you trying to write a relational database system or solve the problem of finding the name of all the employees that work for a given company? If the latter, then why the need for the relation calculus? It's akin to using calculus to create the formula for the volume of a sphere each time that you need to solve for the volume of a sphere rather than just using the proper formula, which has been proven thousands, if not, millions of times.

--Jeff Moden

RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

Change is inevitable... Change for the better is not.

Helpful Links:
How to post code problems
How to Post Performance Problems
Create a Tally Function (fnTally)

Jonathan AC Roberts SSCoach Points: 18361 More actions · Answer 2

spectra - Sunday, October 21, 2018 9:33 PM
I'm solving a problem using tuple relational calculus ( TRC) in DBMS.
Problem
Find the name of all the employees who work for XYZ Bank Corporation.
Solution ( as given in my book)
I don't understand why book is using S . We have t . Since both of them represents tuples , we could just use t in place of S and get moving.
Can anyone please explain why we required S ?

I think it's just say where t is a member of something that exists in S

spectra SSCarpal Tunnel Points: 4120 More actions · Answer 3

Jonathan AC Roberts - Monday, October 22, 2018 7:13 AM
spectra - Sunday, October 21, 2018 9:33 PM
I'm solving a problem using tuple relational calculus ( TRC) in DBMS.
Problem
Find the name of all the employees who work for XYZ Bank Corporation.
Solution ( as given in my book)
I don't understand why book is using S . We have t . Since both of them represents tuples , we could just use t in place of S and get moving.
Can anyone please explain why we required S ?
I think it's just say where t is a member of something that exists in S

Could not get you. Could you please elaborate more ?

Jonathan AC Roberts SSCoach Points: 18361 More actions · Answer 4

spectra - Monday, October 22, 2018 9:08 AM
Jonathan AC Roberts - Monday, October 22, 2018 7:13 AM
spectra - Sunday, October 21, 2018 9:33 PM
I'm solving a problem using tuple relational calculus ( TRC) in DBMS.
Problem
Find the name of all the employees who work for XYZ Bank Corporation.
Solution ( as given in my book)
I don't understand why book is using S . We have t . Since both of them represents tuples , we could just use t in place of S and get moving.
Can anyone please explain why we required S ?
I think it's just say where t is a member of something that exists in S
Could not get you. Could you please elaborate more ?

t is the set of all tuples that exist in S that are a member of the WORKS formula.

spectra SSCarpal Tunnel Points: 4120 More actions · Answer 5

Jonathan AC Roberts - Monday, October 22, 2018 10:19 AM
spectra - Monday, October 22, 2018 9:08 AM
Jonathan AC Roberts - Monday, October 22, 2018 7:13 AM
spectra - Sunday, October 21, 2018 9:33 PM
I'm solving a problem using tuple relational calculus ( TRC) in DBMS.
Problem
Find the name of all the employees who work for XYZ Bank Corporation.
Solution ( as given in my book)
I don't understand why book is using S . We have t . Since both of them represents tuples , we could just use t in place of S and get moving.
Can anyone please explain why we required S ?
I think it's just say where t is a member of something that exists in S
Could not get you. Could you please elaborate more ?
t is the set of all tuples that exist in S that are a member of the WORKS formula.

S is not a tuple ?