Weak Entity Sets in Relational Databases
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Questions and Answers

What is the main function of a foreign key constraint in a one-to-one relationship?

  • To allow multiple references from one table to another.
  • To create duplicates in the related tables.
  • To enforce referential integrity between related entities. (correct)
  • To randomly assign unique identifiers to records.

    • What happens if a unique constraint is not applied to the foreign key in a one-to-one relationship?

  • The relationship will become one-to-many. (correct)
  • The data integrity will improve.
  • Referential integrity is guaranteed.
  • The uniqueness of records will still be maintained.

    • Which statement correctly describes the role of a composite primary key in a one-to-one relationship?

  • It ensures a unique record for each related entity pair. (correct)
  • It eliminates the need for foreign keys.
  • It reduces redundancy in the schema.
  • It allows for multiple relationships between two entities.

    • How does placing a unique constraint on both foreign keys in a one-to-one relationship affect data integrity?

    <p>It prevents duplicate entries across both tables.</p> Signup and view all the answers

    Why is a unique constraint essential in a one-to-one relationship between the Student and Advisor tables?

    <p>It ensures every student can be paired with only one advisor.</p> Signup and view all the answers

    What is a potential issue if referential integrity is not enforced in a relational database?

    <p>Inconsistent data relationships can occur.</p> Signup and view all the answers

    In which case would inserting a record lead to an insertion anomaly in a one-to-one relationship?

    <p>When both foreign keys allow null values.</p> Signup and view all the answers

    What would be the consequence of having a foreign key that is not unique in a one-to-one relationship?

    <p>Multiple records could become associated with a single entity.</p> Signup and view all the answers

    What is a defining characteristic of a superkey?

    <p>It may contain redundant attributes.</p> Signup and view all the answers

    How does a candidate key differ from a superkey?

    <p>A candidate key is always minimal, while a superkey might not be.</p> Signup and view all the answers

    Which statement is true about primary keys in a relational database?

    <p>A primary key uniquely identifies each record in a table.</p> Signup and view all the answers

    When a table has multiple candidate keys, which is selected as the primary key?

    <p>Any of the candidate keys can be selected.</p> Signup and view all the answers

    If a superkey {A, B, C} is given, which of the following could represent a valid candidate key?

    <p>{A, B}</p> Signup and view all the answers

    Can a foreign key function as a primary key within the same relation?

    <p>Yes, if it is also a candidate key.</p> Signup and view all the answers

    Which of the following properties is essential for every primary key in a relational database?

    <p>It must contain no NULL values.</p> Signup and view all the answers

    What is the primary purpose of a candidate key?

    <p>To uniquely identify records with the minimum attributes.</p> Signup and view all the answers

    What ensures that every employee must have an associated department in the Employee table?

    <p>The NOT NULL constraint</p> Signup and view all the answers

    If a foreign key allows NULL values, what is a likely consequence in terms of participation?

    <p>Partial participation is allowed</p> Signup and view all the answers

    Which of the following best defines total participation in the context of relational databases?

    <p>Each entity in a set must be linked to another entity in a different set</p> Signup and view all the answers

    In the Employee table, what does the foreign key refer to?

    <p>Department_ID</p> Signup and view all the answers

    Which statement accurately describes the implications of a foreign key with a NOT NULL constraint?

    <p>An employee must belong to at least one department</p> Signup and view all the answers

    What role does the CHECK constraint play in the definition of the foreign key?

    <p>It enforces that Department_ID cannot be NULL</p> Signup and view all the answers

    What happens to an employee's record if their Department_ID does not have a corresponding entry in the Department table?

    <p>It creates a data integrity error</p> Signup and view all the answers

    Which constraint combination ensures that no employee record can exist without a valid department association?

    <p>Foreign key and NOT NULL constraints</p> Signup and view all the answers

    What is the primary purpose of a unique constraint in a one-to-one relationship?

    <p>It guarantees that there are no duplicate entries in both tables.</p> Signup and view all the answers

    Which approach ensures that an employee can be assigned only one parking space in a database?

    <p>Utilizing a foreign key with a unique constraint on Parking_Space_ID.</p> Signup and view all the answers

    What could happen if no unique constraint is applied to the foreign key in a one-to-one relationship?

    <p>It could potentially degrade to a one-to-many relationship.</p> Signup and view all the answers

    Which statement best describes a violation of a one-to-one relationship constraint?

    <p>A foreign key in Person is not unique among the entries.</p> Signup and view all the answers

    To enforce one-to-one cardinality when a foreign key is placed in only one of the related tables, what action should be taken?

    <p>Apply a unique constraint to the foreign key.</p> Signup and view all the answers

    If a relationship between Person and SSN violates one-to-one relationship constraints, what could be a possible reason?

    <p>There are duplicate SSNs assigned to different persons.</p> Signup and view all the answers

    Why might a foreign key appear in only one of the tables in a one-to-one relationship?

    <p>To save storage space and reduce redundancy.</p> Signup and view all the answers

    What is the consequence of a foreign key being nullable in a one-to-one relationship?

    <p>It can create optional dependencies between tables.</p> Signup and view all the answers

    What is a typical outcome of merging two entity sets that share a primary key?

    <p>Elimination of redundancy.</p> Signup and view all the answers

    In a one-to-many relationship, which of the following constraints is generally applied to the foreign key?

    <p>NOT NULL</p> Signup and view all the answers

    What is often introduced in a many-to-many relationship to manage the association?

    <p>Junction table</p> Signup and view all the answers

    If a shared attribute is moved to a separate entity, the process exemplifies which concept?

    <p>Normalization</p> Signup and view all the answers

    What is the main purpose of a foreign key relationship in the relational model?

    <p>To ensure referential integrity</p> Signup and view all the answers

    Why do weak entity sets exist if they can be converted into strong entities?

    <p>They rely on identifying entities for existence.</p> Signup and view all the answers

    Which design change is most appropriate for two entity sets that have a one-to-one relationship?

    <p>Merge the two entity sets into one.</p> Signup and view all the answers

    What happens when attributes are moved to a separate entity set?

    <p>Normalization occurs.</p> Signup and view all the answers

    Study Notes

    Weak Entity Sets in Relational Databases

    • Weak entity sets are used when entities lack their own unique identifier, relying upon a separate identifying entity for existence and identification.
    • The identifying entity's primary key is crucial for deriving a primary key for the weak entity set.
    • Weak entity relationships are often represented by partial keys which is a combination of the identifying entity's primary key and a unique attribute within the weak entity set.
    • The presence of weak entity set implies a strong relationship between the entities.
    • Weak entity sets signify a fundamental design principle for relational databases for ensuring data integrity and promoting a clear structure of relationships.

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    Description

    This quiz covers the concept of weak entity sets in relational databases, detailing how they depend on identifying entities for their unique identification. It discusses the role of primary keys in weak entities and emphasizes their importance in maintaining data integrity and structure within relational designs.

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