Questions tagged [relational-calculus]
15 questions
1
vote
1 answer
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 formula in relational calculus to an SQL query…
zpavlinovic
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0 answers
Relational calculus: "Find all X with at least y amount of Z"
Assuming I have two relations:
Supplier [ID (PK), Name, City, Country] and
Item [ID (PK), Name, Department, Price, Stock, Supplier_ID (FK)]
What would be the easiest way to determine the following statement both in domain and tuple relational…
T.E.
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1
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0 answers
Division in tuple relational calculus
$ \newcommand{\Set}[2]{%
\{\, #1 \mid #2 \, \}%
}$
I've been trying to find how to express relational division operation in tuple relational calculus. The only thing I found is this presentation where on the page 4 it is said that for relations $R…
tomashauser
- 127
- 4
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1 answer
Check if a relation is reflexive, symmetric and transitive
I want to better understand how this actually works, as my solutions are
sometimes not 100% correct.
I have the following relation:
Check if the following relation is reflexive, symmetric, and/or
transitive:
$$ R_1 = \{ (x,y) \mid x,y \in…
Prometheus
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- 5
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Relational calculus expression for projection (Database Management)
I recently came across this question:
Let the following relation schemas be given:
$R=(A,B,C)$
$S=(D,E,F)$
Let relations r(R) and s(S) be given. Give an expression in the tuple relational
calculus that is equivalent to the following:
a.…
Abhilash Mishra
- 323
- 5
- 16
0
votes
1 answer
Use of existential quantifier in tuple relational calculus
It is somewhat confusing to me when to use quantifiers in tuple relational calculus (TRC). I stumbled upon following problem and I am still scratching my head thinking why not TRC query can be constructed without using existential quantifier.
The…
RajS
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0
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2 answers
Logical equivalence priority
I have the logical formula
$$
A \Leftrightarrow B \Leftrightarrow C
$$
In order to make the truth table I'm not sure wheither I should interpret it as
$A \Leftrightarrow B \Leftrightarrow C$ or $A \Leftrightarrow (B \Leftrightarrow C)$
Here is my…
tixerauRIP
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- 3
0
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0 answers
Is it possible to convert any relational algebra expression into a relational calculus expression?
Let's for the sake of simplicity only focus on tuple relational calculus.
Every relational algebra query can be broken down into the 5 atomic operations - projection, selection, set union, set difference, cartesian product (I'm excluding renaming as…
tomashauser
- 127
- 4
0
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1 answer
Tuple relational calculus: existential quantifiers
I have the following question and given answer:
Question: List the names of managers who have at least one dependant.
Answer: {e.Fname, e.Lname | EMPLOYEE(e) AND (∃d)(∃t)(DEPARTMENT(d) AND DEPENDANT(t) AND e.Ssn = d.Mgrssn AND t.Essn = e.Ssn) }
My…
pk00
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Relation Closure for F+
$A \rightarrow B C$
$C D \rightarrow E$
$B \rightarrow D$
$E \rightarrow A$
I have these Relations for R={A,B,C,D,E}
Now I have to calculate the closure $F^+$ and give the candidate keys
I came to these relations
$A \rightarrow A$
$A \rightarrow…
Rapiz
- 53
- 5
0
votes
1 answer
Need help understanding the tuple relational calculus
We say that a query in a TRC is a statement of the form $\{T: P(T)\}$, where $T$ is a tuple variable and $P(T)$ is a formula.
Now my question is, what are the possible tuples $T$ to be tested i.e., what are the types and values for tested…
Sepehr23
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0
votes
1 answer
Normal form after decomposition of a relation
I came across a text recently which claims that if we perform a lossless decomposition of a relation R into smaller relations R1 and R2, and if R is in 3NF, both R1 and R2 are 3NF.
I felt a bit suspicious regarding this claim, but couldn't find…
Abhilash Mishra
- 323
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- 16
0
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1 answer
Whether same output is obtained for the two queries
Consider the following SQL Queries executed on the relation Employee:
Employee (Eid, Ename, sal)
Eid is the primary key
Queries:
S1:SELECT count (*) FROM Employee;
S2: SELECT count (Eid) FROM Employee;
Will these queries return the same result…
Abhilash Mishra
- 323
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- 16
0
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1 answer
Normal form of relation R
It is given that for a relation R all the attributes of the relation appear in some of the candidate keys. It is also given that there is only one compound candidate key which exists for a relation, all the other candidate keys are simple candidate…
Abhilash Mishra
- 323
- 5
- 16
-1
votes
2 answers
Intuition for a projection in tuple relational calculus
Let's have a relation $R = (name, surname, age)$. I want to obtain a new relation with only the $name$ attribute. In relational algebra I would simply do $\Pi_{\mathrm{name}}(R)$ but in relational calculus the general way of doing that…
tomashauser
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