Question :

Explain Domain Key Normal Form DKNF with example.

Subject

Database Management System

Standard

Computer Science Engineering

Views

638

Asked By

Alexandria

Knowledge
Answer / Solution

Domain Key Normal Form (DKNF) is the highest level of database normalization, ensuring that a relational database schema is free from all modification anomalies. It goes beyond the Boyce-Codd Normal Form (BCNF) and addresses additional constraints that BCNF might not capture. DKNF requires that all constraints in a database be explicitly defined using integrity constraints.

Knowledge
Answer / Solution

To understand DKNF, let's first review the concept of functional dependency. In a relational database, a functional dependency occurs when the value of one or more attributes determines the value of another attribute. For example, in a table of employees, the employee ID uniquely determines the employee's name, so there is a functional dependency between the employee ID and name.

Now, let's consider an example to explain DKNF. Suppose we have a relational database table called "Orders" with the following attributes: OrderID, CustomerID, ProductID, Quantity, and TotalPrice. The primary key of this table is the combination of OrderID and ProductID.

In BCNF, we would ensure that for every functional dependency, the determinant (attributes determining other attributes) is a candidate key. However, BCNF may not address all constraints, leading to anomalies like redundancy, update anomalies, or insertion anomalies.

To achieve DKNF, we need to explicitly define integrity constraints to ensure that the table is free from all these anomalies. In our example, let's say we have an additional constraint that each order should have a unique CustomerID associated with it. This constraint is not captured by BCNF but can be enforced using an integrity constraint.

To satisfy DKNF, we would modify the table structure as follows:

  • Orders(OrderID, ProductID, Quantity, TotalPrice)
  • OrderCustomer(OrderID, CustomerID)

By splitting the original "Orders" table into two separate tables, we create a one-to-one relationship between OrderID and CustomerID. Now, we can enforce the constraint that each order has a unique CustomerID without introducing any anomalies.

In summary, DKNF ensures that a relational database is free from all modification anomalies by explicitly defining integrity constraints and going beyond the requirements of BCNF. It is the highest level of normalization, providing a solid foundation for maintaining data integrity in a database.

Knowledge
Answer / Solution

Domain Key Normal Form (DKNF) is a higher level of normalization in database design that extends the concepts of the Third Normal Form (3NF) and Boyce-Codd Normal Form (BCNF). It ensures that a database schema is free from all possible redundancy and dependency anomalies by addressing the constraints imposed by the domain, key, and integrity rules.

To understand DKNF, let's first discuss the concept of a superkey. A superkey is a set of attributes that uniquely identifies a tuple (row) in a relation (table). A candidate key is a minimal superkey, meaning it cannot have any redundant attributes.

Now, let's define the DKNF. A relation is said to be in DKNF if and only if every constraint on the relation is a logical consequence of the domain constraints and the key constraints. In simpler terms, DKNF ensures that all constraints in a relation are derived solely from the domains and keys of the relation.

Here's an example to illustrate DKNF:

Consider a database schema with two relations: "Customers" and "Orders."

Customers (CustomerID, CustomerName, CustomerEmail) Orders (OrderID, CustomerID, ProductName, Quantity)

In this example, the CustomerID attribute in the Orders relation is a foreign key referencing the primary key CustomerID in the Customers relation. We can assume that CustomerID is the primary key in the Customers relation.

To determine if the schema is in DKNF, we need to check if all the constraints are derived from domain and key constraints.

Domain Constraints:

  • CustomerID in Customers relation must be unique.
  • CustomerEmail in Customers relation must be a valid email address.
  • OrderID in Orders relation must be unique.
  • Quantity in Orders relation must be a positive integer.

Key Constraints:

  • CustomerID is the primary key in the Customers relation.
  • OrderID is the primary key in the Orders relation.

If all the constraints in the schema can be derived from these domain and key constraints, then the schema is in DKNF.

For example, we can derive the following constraint: "A customer cannot place an order if the customer does not exist in the Customers relation." This constraint can be derived from the foreign key constraint between CustomerID in the Orders relation and CustomerID in the Customers relation.

Overall, DKNF ensures that all constraints in a database schema are logically derived from the domain and key constraints. It eliminates redundancy and dependency anomalies, leading to a well-structured and normalized database design.


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