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Questions and Answers
What does the entity integrity constraint ensure regarding primary key values?
What does the entity integrity constraint ensure regarding primary key values?
Which statement best describes referential integrity?
Which statement best describes referential integrity?
In the context of a foreign key, what is required of the attributes in FK?
In the context of a foreign key, what is required of the attributes in FK?
What does it mean if a foreign key value is NULL in the referencing relation?
What does it mean if a foreign key value is NULL in the referencing relation?
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Which of the following statements is NOT a characteristic of primary keys?
Which of the following statements is NOT a characteristic of primary keys?
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What is the role of a foreign key in relation to referential integrity?
What is the role of a foreign key in relation to referential integrity?
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If a foreign key in EMPLOYEE references the Dnumber in DEPARTMENT, what must be true?
If a foreign key in EMPLOYEE references the Dnumber in DEPARTMENT, what must be true?
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What happens if a primary key in the referenced relation is updated?
What happens if a primary key in the referenced relation is updated?
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What does a referential integrity constraint from R1 to R2 ensure?
What does a referential integrity constraint from R1 to R2 ensure?
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In the EMPLOYEE relation, what does the Dno attribute represent?
In the EMPLOYEE relation, what does the Dno attribute represent?
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Which attribute serves as a foreign key that references the EMPLOYEE relation itself?
Which attribute serves as a foreign key that references the EMPLOYEE relation itself?
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How can referential integrity constraints be visually indicated in a relational database schema?
How can referential integrity constraints be visually indicated in a relational database schema?
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What requirement must be fulfilled for a foreign key to reference another relation?
What requirement must be fulfilled for a foreign key to reference another relation?
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When can a foreign key in the EMPLOYEE relation be set to NULL?
When can a foreign key in the EMPLOYEE relation be set to NULL?
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What is a common method for specifying integrity constraints in a relational database?
What is a common method for specifying integrity constraints in a relational database?
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What role do referential integrity constraints play in a relational database?
What role do referential integrity constraints play in a relational database?
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Study Notes
Entity Integrity
- Entity integrity constraint ensures no primary key value can be NULL; it is essential for identifying individual tuples in a relation.
- NULL primary key values result in ambiguous identification, complicating tuple references.
Referential Integrity
- Referential integrity constraint maintains consistency between tuples in two relations.
- A tuple must refer to an existing tuple in another relation for the referential integrity to hold.
- Example: In the EMPLOYEE relation, the Dno attribute must match existing Dnumber values in the DEPARTMENT relation.
Foreign Keys
- A foreign key in relation schema R1 references relation R2 based on specific rules:
- Attributes in the foreign key (FK) share the same domain as primary key attributes (PK) in R2.
- A value of FK in relation R1 must either correspond to a PK value in R2 or be NULL.
- R1 is referred to as the referencing relation, while R2 is the referenced relation.
Relationships in Databases
- Referential integrity constraints often arise from relationships between different entity schemas in a database.
- Example: In EMPLOYEE, Dno indicates the department an employee works for, which is a foreign key pointing to DEPARTMENT.
Self-Referencing Foreign Keys
- A foreign key can refer to its own relation, as seen with the Super_ssn attribute in EMPLOYEE, indicating an employee's supervisor.
- Example: John Smith references Franklin Wong as his supervisor within the EMPLOYEE relation.
Diagrammatic Representation
- Referential integrity constraints can be visually represented with directed arcs showing relationships between foreign keys and their referenced tables.
- Arrowheads point to primary keys of the referenced relations for clarity.
Database Schema and Integrity Constraints
- All integrity constraints need to be defined within the relational database schema for enforcement by the DBMS.
- Data Definition Language (DDL) provisions allow for the specification of various constraints to ensure rules are automatically enforced.
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Description
This quiz covers essential concepts related to entity integrity, referential integrity, and the role of foreign keys in relational databases. Understanding these principles is crucial for maintaining the integrity and reliability of database systems. Test your knowledge and grasp of these foundational elements.