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2 votes

Relational calculus to SQL

I am somewhat aware of the correspondence between (tuple and domain) relational calculus, relational algebra, and SQL. To the best of my understanding, one should be able to automatically convert a ...
AntC's user avatar
  • 487
1 vote

Use of existential quantifier in tuple relational calculus

Something like { c.name | ... } is shorthand for something like {z : (name) | (∃c) (z.name = c.name ^ ...) }. As described ...
Derek Elkins left SE's user avatar
1 vote
Accepted

Tuple relational calculus: existential quantifiers

Let me concentrate, as you asked, on section $(\exists d)(\exists t)(\cdots)$. In case when one part of conjuction is "not depend" on letter under existence quantifier, holds $$(\exists d)(A ...
zkutch's user avatar
  • 2,364
1 vote
Accepted

Check if a relation is reflexive, symmetric and transitive

"If xRy and yRz": Look at the definition of R. You have x = 0 and y ≥ 0 because xRy. You have y = 0 and z ≥ 0 because of yRz. If you have xRy and yRz then you have x = 0 and z ≥ 0, therefore ...
gnasher729's user avatar
  • 30.1k
1 vote

Need help understanding the tuple relational calculus

From Wikipedia: A tuple is of the form $T=(D,R,h)$ where $D$ is the domain, $R$ is a set of relation names, and $h$ is a mapping that associates a column name to each relation in $R$. To represent a ...
BearAqua in Agua's user avatar
1 vote
Accepted

Normal form after decomposition of a relation

I think you are wrong. Here is a rough sketch of a proof (by contradiction) that the original claim is true. Suppose that the claim is false: this means that R1 or R2 (or both) are not in 3NF. ...
Renzo's user avatar
  • 809
1 vote

Whether same output is obtained for the two queries

where Eid field is empty. What do you mean by "empty"? Perhaps you mean 'null'? What words exactly does your "solution manual" use? "empty" or "null"? If the Eid ...
AntC's user avatar
  • 487
1 vote
Accepted

Normal form of relation R

If you bring the functional dependencies of R in a canonical form, you can have only dependencies in which the right part is constituted only by a single attribute, which is prime, so we are sure that ...
Renzo's user avatar
  • 809

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