Mathematics Stack Exchange
Mathematics Stack Exchange

Questions tagged [relation-algebra]

For questions about the algebra used for modeling the data stored in relational databases.

87 questions
4
votes
2 answers

Software for testing relational algebra

Does anyone know of any software to let you test relational algebra queries? By this I don't mean a database such as MySQL, something where the query can be input in some for of mathematical notation instead of SQL.
jamesj
  • 153
3
votes
3 answers

Where can I find good information, tutorials and or examples on relational algebra queries?

Taken a break from my personal project and getting some work done. I would like to find some examples, tutorials on relation algebra. Anything with good examples will be very useful
Psychonetics
1
vote
1 answer

Relational Algebra : Cross Product of a Relation with Table-Dum & Table-Dee

I am wondering what would be the result of the following operation: Let $A$ be a relation with $n$ ($n > 0$) attributes and $t$ ($t > 0$) tuples. Let $TableDum$ be a relation with $0$ attributes and $0$ tuples. Let $TableDee$ be a relation with $0$…
Ludovic
  • 31
  • 3
1
vote
1 answer

What does it mean for a relation algebra to be simple?

I am reading "Boolean Algebras with Operators part II" by Bjarni Jonsson and Alfred Tarski. On theorem 4.10 (p.132-133), they refer to a relation algebra $\mathfrak{A}$ being "simple" and proves that it is equivalent to $\mathfrak{A}$ having no…
MathTeacher
  • 1,559
1
vote
1 answer

Proof - Projection distribution over set union

I've just started databases and have exercise to proof that projection$(\pi)$ is distributive over set union$(\bigcup)$. But I suck in proofs and don't really know how to proof that: $\pi_\alpha( R \bigcup S) = \pi_\alpha(R) \bigcup \pi_\alpha(S)…
Damaon
  • 287
1
vote
1 answer

Relational Algebra: Showing equality using aggregate operator

The schemas are given here for relations $R$ and $S$: $$R(A,B)$$ $$S(C,D,E)$$ One can see that the following equality is true: $$\gamma_{B,sum(E)}(R\Join_{A=C}S) = \gamma_{B,sum(E)}(R\Join_{A=C} ({\gamma_{C,sum(E)}}S))$$ After changing the aggregate…
modulitos
  • 157
1
vote
0 answers

How can I use relational algebra to determine when changes to a relation invalidate the results of an expression?

My goal is to take a series of modifications to relations in an SQL database, and check if I need to re-run other SQL queries because their results would change. Allowing people to listen to changes to an SQL query. I found a similar problem is "how…
vaughan
  • 111
1
vote
0 answers

Relational Algebra Operator Tree

Context: All customer pairs (C1,C2) such that C1 likes some pizza that C2 does not like. LikeDislike(cname, cname2): Question: Find all customer pairs (C1,C2) such that C1 < C2 and they like exactly the same pizzas. Answer: I'm not sure about…
user8779054
  • 55
  • 1
  • 11
1
vote
0 answers

Equivalence between Basic Relational Algebra

The following relation schema: R(A,C), S(A,D), T(X,Y). Primary key attributes bolded Would like to know why the following two are not equivalent queries $Q_1 = π_A (σ_{C<10}(R))$ and $Q_2 = σ_{C<10}(π_A(R))$ The answer: $Q_2$ Invalid expression as…
user8779054
  • 55
  • 1
  • 11
1
vote
0 answers

Must relational algebra use tuples?

Please excuse me if I make glaring mistakes below – I'm a software engineer rather than a mathematician or logician, but I'm trying! My understanding of relational algebra is that relation headings and their body sets are defined in terms of…
Benjohn
  • 137
1
vote
0 answers

Relational Database Reductions

So In the study guide for our Db Design final, the professor gave us this Information preserving logical design, Where bold is a primary key and italics are a foreign key. L1: Donor: D_ID, D_Name, [0, L1, 1]D_Spouse[0, N, 1], [1, L5, 1]D_CI_ID[1,…
James Falter
  • 11
0
votes
0 answers

Need review of Relational Algebra

These are technically homework but I'd like to have verified whether what I did is right or wrong, so I don't upright ask for a solution at least. • Find the names, street address, and cities of residence of all employees who work for “First Bank…
OmniOwl
  • 225
0
votes
1 answer

Equivalence between relational algebra statements

This is a practice question for a relational algebra question which I don't understand. Consider two relations $R(A, B)$ and $S(B,C)$. Which of the following relational algebra expressions is not equivalent to the others? $\pi_{R.A, R.B} (R \Join…
jaynp
  • 2,151
0
votes
0 answers

Cartesian Product and division in relational algebra

I'm pretty sure this question has been asked before, I tried looking for something like it, however, I couldn't find anything. Given two relations $R(A,B),S(B,C)$, assuming S is not empty, prove the following equality: $$(R \times \pi_A(S)) \div…
Aa me
  • 148
0
votes
1 answer

Proving that Selection Operator on Cartesian Product of Two Relations is Equivalent to Theta-Join on Those Same Realtions

As the title suggests, I am trying to prove that $\sigma_\theta(R1\times R2) =R1 \bowtie_\theta R2$. However, as far as I know, the very definition of $\theta$-join is the LHS equation from above, so I am quite confused as to how I should generate a…
ProfileHandle
  • 1
1
2