Relational Model
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Questions and Answers

Which of the following is a possible meaning of a null value in a relation?

  • The value is unknown (correct)
  • The value is not applicable
  • The value does not exist
  • The value is not available

    • What can be interpreted as a fact in a relation?

  • The declaration or assertion
  • The relation schema
  • The attributes in the relation
  • Tuples in the relation (correct)

    • Which characteristic of a relation does not require any particular order to be maintained when displaying it as a table?

  • Ordering of tuples within a relation (correct)
  • Ordering of values within a tuple
  • Values and nulls in a tuple
  • None of the above

    • Why are composite attributes not allowed in relational databases?

    <p>Composite attributes are not atomic values</p> Signup and view all the answers

    Which of the following is a condition that a foreign key must satisfy?

    <p>It must be of the same domain as the attribute it refers to</p> Signup and view all the answers

    What is the purpose of a foreign key?

    <p>To establish a relationship between two relations</p> Signup and view all the answers

    Constraints are the ________ or the limitations on data in the database.

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

    The first constraint under schema based constraint is the ________ constraints.

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

    A ________ is a set of attributes that can help in identifying each tuple in relation uniquely.

    <p>super key</p> Signup and view all the answers

    Foreign key must be of the same ______ as the attribute it refers to

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

    What are the conditions that a foreign key must satisfy?

    <p>A foreign key must satisfy two conditions: 1) It has to be of the same domain as the attribute it refers to. 2) The value of the foreign key in a tuple either occurs as a value of the primary key or is null.</p> Signup and view all the answers

    What is the entity integrity constraint?

    <p>The entity integrity constraint states that no primary key value can be null.</p> Signup and view all the answers

    What is the referential integrity constraint?

    <p>The referential integrity constraint states that a tuple in one relation that refers to another relation must refer to an existing tuple in that relation.</p> Signup and view all the answers

    What are the three categories of constraints in the relational model?

    <p>The three categories of constraints in the relational model are inherent model-based constraints, schema-based constraints, and application-based constraints.</p> Signup and view all the answers

    What is a domain constraint?

    <p>A domain constraint specifies that within each tuple or row, the value of each attribute has to be atomic or indivisible. It also checks the data type of the values of each attribute.</p> Signup and view all the answers

    What is a key constraint?

    <p>A key constraint ensures that tuples in a relation are unique. It defines an attribute or set of attributes that can uniquely identify each tuple in a relation.</p> Signup and view all the answers

    Which of the following is a condition that a foreign key must satisfy?

    <p>The value of the foreign key in a tuple must occur as a value of the primary key.</p> Signup and view all the answers

    What is the purpose of a foreign key?

    <p>To refer to the primary key of another relation.</p> Signup and view all the answers

    What is a key constraint?

    <p>A set of attributes that can help in identifying each tuple in a relation uniquely.</p> Signup and view all the answers

    Which category of constraints in the relational model cannot be directly defined in the schemas and are expressed and enforced by the application programs?

    <p>Application based constraints</p> Signup and view all the answers

    What is the purpose of domain constraints in the relational model?

    <p>To restrict the data type of attribute values within each tuple</p> Signup and view all the answers

    What is a key in the context of key constraints in the relational model?

    <p>An attribute that can uniquely identify each tuple in a relation</p> Signup and view all the answers

    What is the purpose of the entity integrity constraint?

    <p>To ensure that no primary key value can be null</p> Signup and view all the answers

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