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20 Top Question on DBMS
13 February 2023
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DBMS
Top 20 question in DBMS
Write a short notes on Integrity constraints
Integrity constraints in DBMS are used to ensure the correctness and consistency of data stored in a database. There are several types of integrity constraints that can be applied to a database, including:
- Entity Integrity: This ensures that each record in a table has a unique identifier, often in the form of a primary key.
- Referential Integrity: This ensures that relationships between tables are maintained, and that foreign keys in one table reference existing records in another table.
- Domain Integrity: This ensures that values in a table adhere to specific data types and formats.
- Check Integrity: This ensures that values in a table satisfy certain conditions or rules.
Explain Armstrong's axioms.
Armstrong's axioms, also known as Armstrong's rules, are a set of inference rules used in relational database theory to test the semantic integrity of functional dependencies in a relation. These rules are named after William W. Armstrong, who first introduced them in 1974.
The three basic rules of Armstrong's axioms are as follows:
- Reflexivity: If A is a set of attributes and B is a subset of A, then A → B (i.e., A functionally determines B) is true.
- Augmentation: If A → B is true and C is a set of attributes, then AC → BC is also true.
- Transitivity: If A → B and B → C are both true, then A → C is also true.
These three rules can be used to derive additional rules, such as decomposition, union, and pseudotransitivity. By using these axioms, we can identify the functional dependencies that hold within a relation, which can be used to ensure data integrity and optimize database design.