In database management systems, candidate key determination is a crucial process that helps identify the minimal set of attributes that can uniquely identify each tuple or row in a relational database table. These candidate keys serve as a basis for establishing relationships between tables and ensuring data integrity.

Why Candidate Key Determination is important?

Determining the candidate keys is essential for proper database design and normalization. It helps eliminate redundant data and ensures that each tuple is uniquely identifiable. By identifying the candidate keys, we can establish relationships between tables in a database, define primary keys, and establish referential integrity.

How to Determine Candidate Keys?

To determine the candidate keys for a given relational table, we need to follow these steps:

1. Identify the attributes (columns) within the table.

2. Analyze the functional dependencies between attributes. A functional dependency exists when the value of one attribute uniquely determines the value of another attribute.

3. Determine the closure of each attribute set. The closure of an attribute set is the set of all attributes that can be determined by that set through functional dependencies.

4. Identify the attribute sets that satisfy the key properties: uniqueness and minimality. A candidate key should uniquely identify each tuple, and it should not be a subset of any other candidate key.

Example

Let’s consider a simple example to illustrate the process of determining candidate keys. Suppose we have a table representing students in a college:

Table: Students
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| Student_ID | Name | Age |
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|    1       | John |  20 |
|    2       | Jane |  21 |
|    3       | Alex |  19 |
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In this example, the Student_ID column uniquely identifies each student, so it can be a candidate key. Similarly, the combination of Name and Age is also unique for each student, making it another candidate key.

Thus, the candidate keys for this table are {Student_ID} and {Name, Age}.

Conclusion

Determining candidate keys is a crucial step in database design. It helps ensure data integrity and establishes relationships between tables. By identifying the minimal set of attributes that can uniquely identify each tuple, we can define primary keys and maintain the quality and consistency of our data.

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