Partial Dependency in DBMS

The functional dependency (FD) that a relation holds happens to be partial when the removal of one determining attribute gives a functional dependency that holds in the given relation. The FD that is not partial refers to being full.

In this article, we will take a look at the Partial Dependency in DBMS according to the GATE Syllabus for CSE (Computer Science Engineering). Read ahead to learn more.

Table of Contents

• What is Partial Dependency in DBMS?
• When does Partial Dependency occur?
  • Example
• Practice Questions on Partial Dependency in DBMS
• FAQs

What is Partial Dependency in DBMS?

The FD (functional dependency) A->B happens to be a partial dependency if B is functionally dependent on A, and also B can be determined by any other proper subset of A. For instance, we have a relationship like MO->N, M->P, and P->N. In this case, M is alone capable of determining N. It means that N is dependent partially on MO.

When does Partial Dependency occur?

A partial dependency would occur whenever a non-prime attribute depends functionally on a part of the given candidate key. The 2NF (Second Normal Form) eliminates partial dependency. Let us take an example to understand this.

Example

<Employee_Task>

In the table given above, we have a partial dependency. Here is how:

Here, the prime key attributes are Employee_ID and Task_No, and also:

Employee_ID = A unique ID of the employee

Employee_Name = Name of the employee

Task_No = A unique ID of the task

Task_Name = The name of the task

As stated above, the non-prime attributes are Employee_Name and Task_Name. These must be dependent functionally on the part of the candidate key so as to be Partial Dependent.

The Employee_Name can be determined using the Employee_ID. It actually makes the relation Dependent Partially.

The Task_Name can be determined using the Task_No. It makes the relation Dependent Partially.

Thus, the <Employee_Task> relation would violate the Second Normal Form in Normalization and is considered to be a bad database design.

We decompose the tables to remove Partial Dependency along with the violation on the second normal form:

<Employee_Info>

<Task_Info>

Thus, the relation happens to be in the second normal form in the case of Database Normalization.

Practice Questions on Partial Dependency in DBMS

1. The relation that does not consist of any partial dependency happens to be in which of these normal forms?

A. Third

B. Second

C. First

D. BCNF

Answer: B. Second

2. The functional dependency that is present between multiple non-key attributes is known as:

A. Functional dependency

B. Partial transitive dependency

C. Transitive dependency

D. Partial functional dependency

Answer: C. Transitive dependency

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Also Explore,

• Introduction to DBMS
• Lossless Decomposition in DBMS
• Lossy Decomposition in DBMS
• Multivalued Dependency in DBMS
• Decomposition in DBMS
• First Normal Form in DBMS
• Functional Dependency in DBMS
• Normal Forms in DBMS
• Functional Dependency in DBMS
• Transitive Dependency in DBMS
• Join Dependency in DBMS