Relational Data Model Overview
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Questions and Answers

What distinguishes a primary key from other candidate keys in a relation?

  • A primary key can be NULL.
  • A primary key must be underlined. (correct)
  • A primary key can have multiple values.
  • A primary key is always an integer.

    • What does the relational model primarily represent?

  • A collection of programming languages
  • A collection of file structures
  • A collection of data types
  • A collection of relations (correct)

    • What does the entity integrity constraint ensure in a relational database?

  • Unique keys can contain duplicates.
  • All attributes are mandatory.
  • Primary keys can be NULL.
  • No primary key value can be NULL. (correct)

    • In a relation schema denoted by R(A1, A2,...,An), what does 'n' represent?

    <p>The number of attributes in the relation schema</p> Signup and view all the answers

    Which statement best describes referential integrity?

    <p>It maintains consistency across tuples in two relations.</p> Signup and view all the answers

    In a relational database, what constitutes an invalid state?

    <p>At least one integrity constraint is violated.</p> Signup and view all the answers

    What is an attribute in the context of a relational model?

    <p>The role played by a domain in the relation schema</p> Signup and view all the answers

    Which of the following describes a tuple in a relational database?

    <p>An individual entry or row in a table</p> Signup and view all the answers

    What is a characteristic of a foreign key in a relational database?

    <p>It has the same domain as the referenced primary key.</p> Signup and view all the answers

    What is a domain in the context of a relational database?

    <p>A set of atomic values that attributes can have</p> Signup and view all the answers

    Which operation on a relational database can potentially cause a constraint violation?

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

    If a column is designated for 'Age', which of the following could be an appropriate domain?

    <p>Integers ranging from 0 to 120</p> Signup and view all the answers

    Which of the following statements about unique keys is true?

    <p>Unique keys can be NULL but must be unique if not.</p> Signup and view all the answers

    What operation is NOT typically categorized under basic operations that change the states of relations?

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

    Which of the following accurately defines the term 'degree' in relation to a relational database?

    <p>The number of attributes in a relation schema</p> Signup and view all the answers

    What typically corresponds to a real-world entity or relationship in the relational model?

    <p>A tuple in a table</p> Signup and view all the answers

    What is a characteristic of multivalued attributes in a relational database?

    <p>They must be represented by separate relations.</p> Signup and view all the answers

    Which of the following correctly describes composite attributes?

    <p>They should only be stored as their individual components.</p> Signup and view all the answers

    What does a NULL value signify in a database?

    <p>The attribute value is unknown or does not apply to the tuple.</p> Signup and view all the answers

    Which type of constraint can be directly expressed in the schemas of a data model?

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

    Which of the following is an example of an application-based constraint?

    <p>Password length requirement.</p> Signup and view all the answers

    What is meant by domain constraints in a database?

    <p>They specify restrictions on the format of data types.</p> Signup and view all the answers

    How are key constraints defined in a relational database?

    <p>They ensure no two tuples have the same combination of values for all attributes.</p> Signup and view all the answers

    What does it mean when a constraint is inherent to the model?

    <p>It is derived from the rules of the miniworld it represents.</p> Signup and view all the answers

    In relational model notation, what does the notation STUDENT(Name, Ssn,...) imply?

    <p>It refers to a set of tuples in the STUDENT relation schema.</p> Signup and view all the answers

    What is the purpose of domain constraints in a relational database?

    <p>To apply restrictions on attribute values based on type.</p> Signup and view all the answers

    What happens when an insertion violates one or more constraints?

    <p>The insertion is rejected.</p> Signup and view all the answers

    Which of the following is a way to enforce an integrity constraint violation when inserting a department with an existing DNUMBER?

    <p>Reject the insertion.</p> Signup and view all the answers

    What must be done when the Mgr_ssn does not match any existing SSN in the EMPLOYEE relation?

    <p>Change Mgr_ssn to an existing SSN value.</p> Signup and view all the answers

    What type of integrity constraint is violated when an employee with an existing SSN is referenced in a new department entry?

    <p>Referential integrity.</p> Signup and view all the answers

    If an insertion is attempted with a duplicate DNUMBER in the DEPARTMENT table, what type of constraint is violated?

    <p>Key constraint.</p> Signup and view all the answers

    What is the default option for handling inserted records that violate integrity constraints?

    <p>Reject the insertion.</p> Signup and view all the answers

    Which operation is NOT a way to handle key constraint violations during insertion?

    <p>Allow duplicate entries temporarily.</p> Signup and view all the answers

    What is a consequence of inserting a record with a salary that is not in decimal format?

    <p>The record is rejected due to format constraints.</p> Signup and view all the answers

    What happens when a delete operation violates referential integrity?

    <p>The deletion can be restricted or cascaded.</p> Signup and view all the answers

    What does the 'set null' option do in the context of a delete operation?

    <p>It changes the values of the referencing attributes to null.</p> Signup and view all the answers

    What must be specified to avoid issues during an update operation?

    <p>A condition on attributes of the relation.</p> Signup and view all the answers

    What violation occurs when updating a foreign key to a non-existent primary key value?

    <p>Violation of referential integrity.</p> Signup and view all the answers

    When deleting a DEPARTMENT tuple with Dnumber = 1, what integrity constraint is violated?

    <p>Referential integrity.</p> Signup and view all the answers

    What is one way to enforce referential integrity when a delete operation is performed?

    <p>Reject the deletion.</p> Signup and view all the answers

    Which of the following would NOT typically cause problems during an update operation?

    <p>Updating an attribute not part of any key.</p> Signup and view all the answers

    What does the DELETE command shown for the employee table do?

    <p>Deletes specific records based on the given condition.</p> Signup and view all the answers

    Study Notes

    Relational Data Model Overview

    • The relational model emerged with the first commercial implementations in the early 1980s.
    • It has been widely adopted in numerous commercial systems.

    Relational Model Concepts

    • Data is represented as a collection of relations (tables).
    • Each table includes a name (relation name) and consists of rows (tuples).
    • Tuples correspond to a collection of related data values, often representing real-world entities.

    Domains, Attributes, Tuples, and Relations

    • A domain defines a set of atomic values an attribute may hold (e.g., age as integers from 0 to 120).
    • A relation schema is denoted as R(A1, A2,...,An), indicating the relation name R and its attributes.
    • The degree (or arity) of a relation is the number of attributes it contains.

    Characteristics of Relations

    • Multivalued attributes must be represented in separate relations.
    • Composite attributes, like an address, should consist of simple attributes in a basic model.
    • NULL values indicate unknown or inapplicable attributes, with specific meanings such as value unknown or value does not apply.

    Relational Model Notation

    • Relation schema name (e.g., STUDENT) signifies the current set of tuples.
    • Attributes can be qualified with their relation name using dot notation (R.A).

    Relational Model Constraints

    • Constraints impose restrictions on database values, stemming from the miniworld rules.
    • Implied constraints are inherent to the data model (e.g., age must be positive).
    • Explicit constraints can be directly expressed in schema (e.g., age > 18).
    • Application-based constraints are business rules enforced through application programs.

    Domain Constraints

    • Domains can include various data types such as integers, strings, booleans, dates, money, etc.

    Key Constraints and NULL Value Constraints

    • No two tuples can have identical values for all attributes.
    • Candidate keys may exist, and a primary key is designated from these, denoted with an underline.
    • Referential integrity constraints ensure the value of foreign keys corresponds to primary keys.

    Integrity Constraints

    • Entity integrity requires that no primary key value can be NULL.
    • Referential integrity ensures consistency between tuples in different relations.
    • Invalid states fail to meet integrity constraints, while valid states satisfy all specified constraints.

    CREATE TABLE Example

    • An employee table schema example shows attribute types including strings, dates, and decimals.

    Update Operations and Transactions

    • Relational operations are grouped into retrievals and updates, which include insert, delete, and update actions.
    • Each operation can potentially violate constraints; for example, an insert might be rejected if it conflicts with existing constraints.

    The Insert Operation

    • Inserting a new tuple requires specifying attribute values and adhering to constraints.
    • An example shows the correct syntax for inserting data into the employee table.

    DELETE Operation

    • Deletes can violate referential integrity if they remove tuples referenced by foreign keys.
    • Options for enforcing referential integrity include restricting the delete, cascading the delete, or setting values to NULL.

    The Update Operation

    • Updates require conditions to select tuples for modification.
    • Changing primary/foreign key values can lead to integrity constraint violations.

    These notes serve as a structured overview of the relational model, its components, constraints, and standard operations, useful for understanding the foundations of relational databases.

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    Elmasri_6e_GE Ch 3 (1).ppt

    Description

    This quiz covers the fundamental concepts of the relational data model as outlined by Ramez Elmasri and Shamkant Navathe. It delves into the structure of relational databases, including relations, tables, and attributes. Perfect for students studying database systems or computer science.

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