Contents
- 1 Do functional dependencies work both ways?
- 2 How do you know if functional dependencies are equivalent?
- 3 How many functional dependencies can be there in table?
- 4 How do you find the minimal set of functional dependencies?
- 5 Which is the best definition of a functional dependency?
- 6 When to break up a table for functional dependency?
Do functional dependencies work both ways?
A Ward will always have the same number and name making the functional dependency go both ways.
Which type of functional dependency is always valid?
C->C : Valid (Trivial Dependency always valid according to Reflexive Axiom) AB->A : Valid (A’s values are unique hence determinant AB’s values will also be unique, hence dependent A’s value could be anything, AB->any attribute of above relation will be valid)…Example:
| A | B | C |
|---|---|---|
| 5 | 2 | 3 |
| 6 | 3 | 2 |
How do you know if functional dependencies are equivalent?
Definition: Two or more than two sets of functional dependencies are called equivalence if the right-hand side of one set of functional dependency can be determined using the second FD set, similarly the right-hand side of the second FD set can be determined using the first FD set.
Are functional dependencies bad?
Why a bad functional dependency will cause anomalies: Since the LHS (= PNumber) of the functional dependency is not a key: You can have multiple tuples in the database with the same PNumber value.
How many functional dependencies can be there in table?
There are mainly four types of Functional Dependency in DBMS.
What are functional dependencies based on?
The functional dependency is a relationship that exists between two attributes. It typically exists between the primary key and non-key attribute within a table. The left side of FD is known as a determinant, the right side of the production is known as a dependent.
How do you find the minimal set of functional dependencies?
A set of FDs F is minimum if F has as few FDs as any equivalent set of FDs….Simple properties/steps of minimal cover:
- Right Hand Side (RHS) of all FDs should be single attribute.
- Remove extraneous attributes. [What is extraneous attribute? Refer here].
- Eliminate redundant functional dependencies.
How do you do functional dependencies?
A functional dependency is denoted by an arrow “→”. The functional dependency of X on Y is represented by X → Y. Let’s understand Functional Dependency in DBMS with example. In this example, if we know the value of Employee number, we can obtain Employee Name, city, salary, etc.
Which is the best definition of a functional dependency?
Chapter 11 Functional Dependencies. A functional dependency (FD) is a relationship between two attributes, typically between the PK and other non-key attributes within a table.
How are axioms used to infer functional dependencies?
Axioms is a set of inference rules used to infer all the functional dependencies on a relational database. It is a rule that suggests if you have a table that appears to contain two entities which are determined by the same primary key then you should consider breaking them up into two different tables.
When to break up a table for functional dependency?
It is a rule that suggests if you have a table that appears to contain two entities which are determined by the same primary key then you should consider breaking them up into two different tables. It is displayed on the right side of the functional dependency diagram.
When is a DBMS dependency a non-trivial dependency?
Non Trivial Functional Dependency in DBMS Functional dependency which also known as a nontrivial dependency occurs when A->B holds true where B is not a subset of A. In a relationship, if attribute B is not a subset of attribute A, then it is considered as a non-trivial dependency.