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  1. Discuss insertion, deletion, and modification anomalies. Why are they considered bad? Illustrate with examples.
  2. What is meant by the closure of a set of functional dependencies?
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Data Anomalies and Functional Dependencies

Data Anomalies

Data anomalies occur when inconsistencies arise in a database due to redundant or missing information. They can lead to data integrity issues, inaccurate reporting, and difficulty in maintaining data consistency.

Types of Anomalies:

  1. Insertion Anomaly: This occurs when it’s impossible to add new data to the database without also adding data to another related table. For instance, in a database without a separate table for customers, it would be impossible to store information about a customer until they make a purchase.

Full Answer Section

 

 

 

  1. Deletion Anomaly: This happens when deleting one piece of data results in the accidental loss of other related data. For example, if a customer table is not normalized, deleting a customer might also delete their order history.
  2. Update Anomaly: This arises when updating data in one place requires updating it in multiple places, leading to inconsistencies. For instance, if a customer’s address is stored in multiple tables, updating it in one place might not update it in all locations.

Closure of a Set of Functional Dependencies

A set of functional dependencies, F, is said to be closed if it contains all the functional dependencies that logically follow from F. In other words, it is closed under implication.

Example:

Consider a relation R(A, B, C) with the following functional dependencies:

  • A -> B
  • B -> C

The closure of F, denoted as F+, would include:

  • A -> B
  • B -> C
  • A -> C (derived from the transitive rule)

Closure is essential in database design as it helps identify redundant data and potential anomalies. By understanding the closure of functional dependencies, database designers can create efficient and reliable database schemas.

References:

  1. Elmasri, R., & Navathe, S. B. (2011). Fundamentals of Database Systems. Addison-Wesley.
  2. Silberschatz, A., Korth, H. F., & Sudarshan, S. (2010). Database System Concepts. McGraw-Hill Education.

 

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