Last Updated on April 17, 2023 by Prepbytes
Multivalued dependency in dbms (MVD) is an important concept in the field of database design and management. It is a logical relationship that exists between the attributes of a relation in a database. MVDs describe the relationship between a set of attributes, and how the values of these attributes relate to each other.
MVDs play a crucial role in ensuring that databases are designed in a way that is efficient, effective, and scalable. They help to reduce redundancy, improve data integrity, and increase the speed and accuracy of data retrieval. Here we will discuss the significance of Multivalued dependency in dbms, its representation, the conditions for its existence, and an example of Multivalued dependency in DBMS along with verification.
What is Multivalued Dependency in DBMS?
MVD stands for multivalued dependency in dbms, which is a concept in database design. MVDs are used to represent dependencies between sets of attributes in a relation, where a change in one set of attributes may result in multiple values for another set of attributes. An MVD X->Y holds if and only if for any two tuples t1 and t2 in the relation R with the same values for attributes in X, there exist two tuples t3 and t4 with the same values for attributes in X and Y such that t1Y = t3Y and t2Y = t4Y.
Multivalued dependency in dbms are important in database normalization, which is the process of organizing a database in a way that minimizes data redundancy and improves data integrity. In normalized databases, each attribute depends only on the primary key and not on any non-key attributes. Understanding MVDs is crucial for designing efficient and scalable databases.
Representation of Multivalued Dependency in DBMS
Multivalued dependency in dbms can be represented using a notation similar to that used for functional dependencies. An MVD is represented by a double-headed arrow (⇒) between two sets of attributes, where the left-hand side (LHS) is a subset of the attributes of the relation, and the right-hand side (RHS) is a subset of the attributes that are not functionally dependent on the LHS. For example, consider a relation R(A, B, C, D), where A → B and B → C. An MVD exists between A and C if A ⇒⇒ C.
Condition for Multivalued Dependency in DBMS Exists
A Multivalued dependency in dbms exists between two sets of attributes X and Y in a relation R if and only if there are two other sets of attributes A and B, where X ⊆ A ⊆ R and Y ⊆ B ⊆ R and A and B are not functionally dependent on each other, but they are functionally dependent on X. In other words, there must be two subsets of R that are functionally dependent on X but are not functionally dependent on each other.
Example of Multivalued Dependency in DBMS
Consider a relation R(S, P, C) that describes the sales of a product P by a salesperson S to a customer C. Assume that each salesperson can sell the same product to multiple customers, and each customer can buy multiple products from the same salesperson. In this case, there is an MVD between S and P if and only if a salesperson can sell multiple products to multiple customers, but the products sold by the salesperson are independent of each other.
To verify the existence of an MVD between S and P, we need to identify two other sets of attributes A and B, where A and B are not functionally dependent on each other, but they are functionally dependent on S and P. Let A = {S, P} and B = {S, C}. We can see that A and B are not functionally dependent on each other, but they are functionally dependent on S and P. Therefore, an MVD exists between S and P in relation to R.
Conclusion
When the values of two independent attributes, say b and c, are determined by the third attribute a, multivalued dependence exists.
The symbol for MVD is ‘a –> b’.
As a result, we can state that in order for a multivalued dependency to exist in a relation R.
Two components of a single attribute, say B and C, should be mutually independent of each other.
For two tuples of R, say A and B, the entire attributes of A may have different values for component B.
Similarly, For two tuples of R, say A and C, the component C may have different values for the entire attributes of A.
The concept of multivalued dependency (MVD) in database design is an extension of the functional dependency (FD) concept. MVDs are used to represent dependencies between sets of attributes in a relation, where a change in one set of attributes may result in multiple values for another set of attributes.
Frequently Asked Questions
Here we have FAQs on multivalued dependency in dbms
Q1. Can an MVD always be replaced by a set of functional dependencies?
Ans. No, not all MVDs can be replaced by a set of functional dependencies. This is because MVDs represent a one-to-many relationship between sets of attributes, which cannot be expressed using functional dependencies. In some cases, a single MVD may be equivalent to multiple functional dependencies, but this is not always the case.
Q2. How do MVDs affect database performance?
Ans. MVDs can affect database performance by introducing data redundancy, which can slow down data retrieval and increase storage requirements. However, MVDs can also improve database performance by enabling more efficient queries and reducing the number of join operations required to retrieve data.
Q3. How are MVDs used in database normalization?
Ans. MVDs are used in third normal form (3NF) and higher levels of normalization to eliminate data redundancy and improve data integrity. By identifying MVDs in a relation, we can split the relation into multiple relations, each containing a subset of the original attributes. This reduces data redundancy and improves data integrity by ensuring that each attribute depends only on the primary key.
Q4. Can MVDs be used in non-relational databases?
Ans. MVDs are primarily used in relational databases, which are based on the relational model. However, the concept of MVDs can be applied to other types of databases, such as graph databases and document databases, where there is a one-to-many relationship between sets of attributes.