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Questions tagged [relational-theory]

On this site this tag applies to questions about Relational Model theory. The Relational Model for database management is an approach to managing data using a structure and language consistent with first-order predicate logic. In the Relational Model of a database, all data is represented in terms of tuples, grouped into relations. A database organized in terms of the Relational Model is a relational database.

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18 views

Entity Relationship Diagram - Entity depending on attribute

I have an ER-Diagram containing the entity employees. When employees have high skills they may supervise lower skilled employees. How can I model that in an ER-Diagram? My initial approach of was to ...
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1answer
34 views

Why is this relation not in Boyce-Codd Normal Form (BCNF)?

I have the relation (A,B,C,D,E). The relevant functional dependencies are: { E,B,C } → { D } { A,B } → { C } { E,B,D } → { C } { E,A,B } → { D } The candidate key is (E,A,B). I do not understand ...
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1answer
46 views

Finding all possible minimal covers

I have a relation schema R = {A, B, C} and the following functional dependencies: A → B A → C B → A B → C C → A C → B How many different minimal covers can I derive from this relation schema? I have ...
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1answer
26 views

What is a “part-key”?

I'm a beginner and student with regards to database design. The tutor recently discussed “part-keys”. I am struggling to find any information on what a part-key is, and I suspect it probably goes by ...
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1answer
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How do I bring a relation/table to first normal form (1NF) when one of the attributes/columns can hold any number of values?

For example, MOVIES (movieid, movietitle) where movietitle can be any number of words, so I believe it's not atomic. How do you bring something like that to 1NF?
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Normalization with two potential primary keys

I have the following STUDENT relation in first normal form, where id has been identified as the primary key (email here is also unique for all tuples): STUDENT(id, email, first_name, last_name) I ...
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38 views

Design issue in transitive dependencies between tables

This is a made-up scenario, but I imagine that it can be of general interest, so I'll post it here. Imagine the following business rule: A course has a grade scale that determines what grades a ...
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2answers
75 views

Does a computed column break 3NF (third normal form)?

From my understanding of 3NF, there should not be any transitive dependency. However, this is what I found from the AdventureWorks2012 database Production.WorkOrder table. Since StockedQty is ...
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1answer
30 views

Show that functional dependency pseudotransivity holds using closure test

I'm currently studying a basic database course with the course literature Database Systems - The Complete Book1. In one of the book's exercises you are asked to Show that the following rules hold,...
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1answer
35 views

Determining minimal cover of a relation

I am having trouble understanding why a certain set of functional dependencies is not minimal. We have a relation R(A,B,C,D,E,F,G) with the following dependencies F: 1. A->CDE 2. B->FG 3. AB-&...
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1answer
165 views

Does using composite keys violate 2NF?

From all of the database related reference books that I have come across, there is a universal rule that state a database table should be at least 3NF. From what I understand, a table is considered ...
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1answer
98 views

Why should foreign keys be implemented in my relational database? [duplicate]

Earlier today, I sparked a rather unexpected debate with my professional peers on the topic of foreign keys in our company's databases. In a nutshell, a software engineer who is senior to me stated ...
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Relational Algebra: how to express the combination of aggregation and projection?

Here I have a table, I would like to query the average salary of departments, the SQL statement should be select dept_name, avg(salary) from employee I try to express this SQL in relational algebra....
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Write aggregate function in select predicate in relational algebra

Can i write aggregate function in select predicate in relational algebra? I am trying to find the maximum salary in the table Employee(name,salary) I am doing this to get max salary. σₛₐₗₐᵣᵧ=Gₘₐₓ₍...
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1answer
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Can and should relational database contain tables that don't have primary keys? [duplicate]

So this site says: "All tables in a relational database should have a primary key". Here it also says that every table should have a primary key. But if I look here and here they say that tables ...
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1answer
31 views

Decompose a relation to 2NF and preserve all the functional dependencies

For example, consider the following relation: R(A, B, C, D, E) With the functional dependencies (FDs) shown below: {A→B, BC→E, D→C} Here candidate key is {AD} and the relation is not in second ...
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0answers
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Is a relation with two attributes always in Boyce-Codd Normal Form (BCNF)?

I went through some tutorials on BCNF and got that a relation with two attributes is always in BCNF. My question What if a relation with two attributes has no prime or non-prime attributes? That is,...
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2answers
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Is a table without a primary key normalized?

In a lecture, my lecturer showed us a table without a primary key. Upon questioning, he said that in 3NF when you remove transitive dependencies it's ok to then have a table without a primary key. ...
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2answers
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Is saving disk space still considered an advantage of normalization?

I have read a while back that one of the advantages of normalization is to save disk space (since normalization minimizes redundancy), but is saving disk space still considered an advantage of ...
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2answers
173 views

Does the concept of candidate key exist only in theory?

I know the concept of candidate key in RDBMS theory, but do candidate keys really exist in actual SQL engines? I mean is there any way to designate a particular column or set of columns as a candidate ...
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0answers
47 views

How To Query Databases in Subject-Predicate Format?

I have csv data in this format: id fieldname fieldvalue -- --------- ---------- 1 fieldA A1 1 fieldB B1 2 fieldA A2 2 fieldA B2 If I upload this to MySQL, how can I ...
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1answer
222 views

What is the meaning of “minimal key”?

In the definition, it says minimal key is a minimal set of attributes needed to identify the table. Does the "minimal" part mean "minimal number of attributes" or "cannot be eliminated"? For example: ...
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0answers
216 views

How to write group by and having in a relational algebra interpreter?

I am practising writing relational algebra (RA) expressions in RA interpreter from Duke, but I can't figure out how to represent group by or having (from SQL). I have this expression, but I need to ...
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Can the Chase test algorithm only modify attributes on the right side of a functional dependency?

I'm attempting to apply the Chase Algorithm to determine if a decomposition is a lossless join decomposition. Functional Dependencies = {A → C, B → D, C → D, DE → C, CE → A} Here is my initial ...
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1answer
181 views

BCNF decomposition does not prevent insert anomaly?

I am in the process of designing a schema for a simple polling app and have tried to normalize it with the decomposition algorithm from this lecture. Requirements A poll has a unique id (poll_id), a ...
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70 views

Equi Join On Union- and Intersection-Compatible Relations

Suppose that I have two union- and intersection-compatible relations; i.e., R1(A,B) and R2(C,D) as: Now , I want to find the join of both relations with equality conditions A=C and B=D. I have ...
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Finding Exclusive Pairings in Relational Algebra

classId | studentId 0 0 0 1 0 2 1 0 1 1 1 2 2 2 How do you find the pairs of students (s1, s2) that ONLY have classes with ...
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1answer
98 views

Inserting data into a 3NF database [closed]

I have 6 tables with ~2-15 attributes each, each one of these 6 tables has an ID which is constrained from another table. This 7th table has its own ID and the 6 other table ID's, as well as a date ...
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82 views

Third Normal Form (3NF) Decomposition Scenario

I am trying to understand what are the steps to check if a decomposition of table is in 3NF. There is a specific exercise I'm trying to solve with no success. Given that R={A1,A2,A3,A4} and F={A1→...
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1answer
130 views

For BCNF decomposition, is it okay to have a relation with none of the original functional dependencies?

Given the relation R[c, f, g, h, e, j, a, b, d, i] with the below functional dependencies I have come up with the below solution. However, I am unsure about it, considering R8 has none of the listed ...
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1answer
50 views

Confusion with Tuple Relation Calculus Operations

I came upon a question like, Given the following relational schemas Student (studId, name, age, sex, deptNo, advisor) Department (deptId, DName, hod, phoneNo) Which of the following will be the ...
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1answer
38 views

Are these relations in BCNF?

I have a homework question that I am trying to understand but having a tough time with this question. Any explanation or even pointers would be very appreciated (no exact answer expected - I am trying ...
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1answer
163 views

Is sql_variant compatible with First Normal Form (1NF)?

1NF rule says that we should not keep data of different types in one single column. Does it mean that sql_variant is not compatible with first normal form hence should not be used?
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1answer
68 views

Questions Concerning the Chase Test

For the question above, my work for each of the questions is below the concerns. Here are my main concerns: Does the order in which you use the relations matter? Can you end up with less tuples with ...
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1answer
39 views

Question concerning minimal/cannonical cover

For the question above, I am confused with how to approach simplifying the left hand side of BDCE->A. Do I get rid of E, as D depends on it, or do I get rid of CD as well, as CD->A? Here's what I ...
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3answers
240 views

What normalization rules does this table break

Our previous DBA got fed up with the development teams frequent requests to change the database schema to add and delete columns. He then advised to the developers that he would create simple tables ...
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1answer
1k views

How to represent NULL in relational algebra?

In the 3rd part of the question below: Study the tables given below and write relational algebra expressions for the queries that follow. STUDENT(+ROLLNO, NAME, AGE, GENDER, ADDRESS, ADVISOR) ...
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1answer
106 views

Is it Important to Understand Each Normal Form?

I have been studying database design and programming for quite some time now, but I still can't get a grasp of understanding each individual normal form (that is, 1NF, 2NF and 3NF). Seeing as anytime ...
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1answer
31 views

Relations and Sets

From my understanding, One = {1,2,3,4,5...20}, and then if Two = {1}, then One won't map into Two. On that token, how come the answer is d instead of a?
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1answer
62 views

Assessing the normal form for a relation with a multi-valued attribute

Assume that you have designed the following schema of relations: COURSES (CID, CNAME) STUDENTS(SID, SNAME, FAV_CIDS) However, you can not have a relation with set valued attributes (Did not really ...
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369 views

Counting in Tuple Relational Calculus

Given the following schema: Staff (sid, sname) Project (pid, pdesc, pfrom, pto) Asset (aid, acat, adesc) Workfor (sid, pid, wfrom, wto) Assignment (aid, sid, pid, afrom, ato) Note: The bold ...
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1answer
228 views

Equivalent of SQL’s “INNER JOIN USING” in relational algebra

I'm following a course in databases (Standford introduction to databases on YT) and, at some point, it's mentioned that t1 INNER JOIN t2 USING attr1, attr2 is equivalent to the NATURAL JOIN symbolized ...
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2answers
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Is there a name for this pattern, representing one-to-many relationships by adding columns with an index to a single table?

So a domain expert wants the following relation: CarOwners(owner_id, name, address, car_1_registration, car_2_registration, car_3_registration, car_4_registration) The reason given that most people ...
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1answer
45 views

If A -> B is augmented with C, is AC -> B legal?

Given the augmentation axiom and the decomposition axioms of functional dependencies and a relation of R(A,B,C) with an FD of: A -> B I can augment A -> B with C to get AC -> BC. Can I then ...
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1answer
119 views

Assessing statement about third normal form

Consider the following statements: A relation R, is in 3NF if every non-prime attribute of R, is fully functionally dependent on some key of R. State True or False. The answer given ...
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1answer
104 views

In which normal form is the relation R?

Hello Community, To prepare for my exam I have completed many exercises. Most of them were solvable without any problems. But the following task I could not solve until now. It is: You are given ...
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2answers
4k views

How does normalization fix the three types of update anomalies?

I have been reading 'Database Systems: A practical approach to design, implementation and management' by Connolly and Begg in order to understand database normalization (chapter 14). I now better ...
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2answers
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Difference between functional dependency and join dependency

By definition, a functional dependency is defined as Let X and Y be subsets of attributes of a relation R. A functional dependency X → Y holds over R if and only if for any instance r of R, ...
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0answers
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Difference Between Implication and Conjunction in Domain Relational Calculus

I was reading my notes, and I came across this: Another example would be to find the names of the lecturers teaching all modules. We might reach for the following incorrect expression: {<N&...
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1answer
95 views

Do my relational algebra operations produce the desired results?

I have these tables: Sailors sid sname rating age --- ------ ------ --- 22 dustin 7 45 31 john 8 55 58 ben 10 35 Boats ...