Relational Data Model Overview
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Questions and Answers

What is the primary purpose of a unique identifier in the United States?

  • To categorize different states.
  • To track employment and tax relations. (correct)
  • To determine academic performance.
  • To assign names to individuals.

Which data type is used for employee ages in a company?

  • Real (floating-point) numbers.
  • Integer values between 15 and 80. (correct)
  • Decimal numbers above 0.
  • Random strings.

What is the relationship between a relation name R and its attributes Ai?

  • Attributes represent the roles played by domains. (correct)
  • The relation name is just a placeholder.
  • Attributes define the relation name.
  • The relation name includes domain definitions.

What is the significance of the degree (or arity) of a relation?

<p>It signifies the number of attributes in the relation schema. (C)</p> Signup and view all the answers

What must be included when defining domains like Person_weights?

<p>Units of measurement such as pounds or kilograms. (A)</p> Signup and view all the answers

Which of the following is NOT a valid format for a domain?

<p>Random alphanumeric characters. (A)</p> Signup and view all the answers

How are academic department names defined in a university context?

<p>As a set of valid character strings. (C)</p> Signup and view all the answers

What defines a relation schema R?

<p>A name and a list of attributes. (A)</p> Signup and view all the answers

What is essential for an attribute to be designated as a key in a relation?

<p>It must be time-invariant and remain unique regardless of new data. (A)</p> Signup and view all the answers

In a relation schema, what is a candidate key?

<p>An attribute that uniquely identifies tuples and can be chosen as a primary key. (D)</p> Signup and view all the answers

Why is it generally discouraged to use names as keys in relation schemas?

<p>Two individuals can share the same name, leading to ambiguity. (C)</p> Signup and view all the answers

What distinguishes a primary key from other candidate keys?

<p>The primary key is selected for its minimal length and uniqueness. (C)</p> Signup and view all the answers

What notation is typically used to represent primary keys in a relation schema?

<p>Underlined attributes (C)</p> Signup and view all the answers

What happens when a relation schema has multiple candidate keys?

<p>One is designated as the primary key while others become unique keys. (B)</p> Signup and view all the answers

Which of the following best defines a superkey?

<p>A superkey is a candidate key that includes additional redundant attributes. (C)</p> Signup and view all the answers

When are multiple candidate keys particularly useful in a relation schema?

<p>When there's a need for multiple ways to access data. (B)</p> Signup and view all the answers

What does the attribute Dno represent in the EMPLOYEE relation?

<p>The department for which an employee works (C)</p> Signup and view all the answers

What condition must a value of Dno satisfy in the EMPLOYEE relation?

<p>It must have a corresponding value in the primary key of DEPARTMENT (D)</p> Signup and view all the answers

Can a foreign key reference its own relation? If so, provide an example.

<p>Yes, Super_ssn in EMPLOYEE refers to another employee as a supervisor. (A)</p> Signup and view all the answers

What is the role of the foreign key in a database?

<p>To ensure referential integrity between relations (C)</p> Signup and view all the answers

In the example provided, which employee references Franklin Wong as a supervisor?

<p>John Smith (A)</p> Signup and view all the answers

How can referential integrity constraints be visually represented?

<p>By drawing a directed arc from each foreign key to the relation it references (D)</p> Signup and view all the answers

What does it mean if a foreign key can be NULL?

<p>The foreign key does not link to any existing entity. (B)</p> Signup and view all the answers

What does a directed arc from a foreign key to a primary key signify?

<p>The foreign key is a foreign reference. (C)</p> Signup and view all the answers

What are state constraints primarily used for in a database?

<p>To define valid states that the database must satisfy (A)</p> Signup and view all the answers

Which of the following correctly describes transition constraints?

<p>They define conditions for data updates and changes (C)</p> Signup and view all the answers

What operation is NOT one of the basic update operations in the relational model?

<p>Alter (D)</p> Signup and view all the answers

Which operation would you use to remove tuples from a relation?

<p>Delete (D)</p> Signup and view all the answers

How does relational algebra primarily assist users in a database?

<p>By allowing formulation of queries to retrieve data (D)</p> Signup and view all the answers

What is a key characteristic that differentiates a relation from ordinary tables or files?

<p>A relation is not sensitive to the ordering of tuples. (A)</p> Signup and view all the answers

Which type of constraint is NOT classified as a database constraint?

<p>Operational constraints (C)</p> Signup and view all the answers

What happens when a database update operation violates integrity constraints?

<p>The operation is automatically rolled back (B)</p> Signup and view all the answers

What is the main purpose of a trigger in a database?

<p>To enforce a certain constraint automatically during a transaction (C)</p> Signup and view all the answers

What does a NULL value in a tuple typically represent?

<p>Missing or unknown information (C)</p> Signup and view all the answers

What is the term used to describe a list of attributes that describes the structure of a relation?

<p>Relation schema (D)</p> Signup and view all the answers

In the context of relational databases, what does the Update operation do?

<p>It alters the values of attributes in existing tuples. (D)</p> Signup and view all the answers

What should be avoided as much as possible in a relational database?

<p>NULL values (C)</p> Signup and view all the answers

What is one of the consequences when a database management system (DBMS) encounters a referential integrity violation?

<p>It may delete offending tuples from related tables. (A)</p> Signup and view all the answers

What happens if a referencing attribute that causes a referential integrity violation is part of the primary key?

<p>It cannot be set to NULL as it would violate entity integrity. (B)</p> Signup and view all the answers

What is an example of a valid response a DBMS can take when a referential integrity violation occurs?

<p>Set the offending attributes to reference a default valid tuple. (D)</p> Signup and view all the answers

What is a potential result of updating an EMPLOYEE tuple's Dno to a value that violates referential integrity?

<p>The operation will be rejected as unacceptable. (A)</p> Signup and view all the answers

When should a database designer specify options for handling referential integrity violations?

<p>During the specified DDL phase. (A)</p> Signup and view all the answers

Which option is NOT available for handling violations of referential integrity constraints?

<p>Automatically back up the entire database... (D)</p> Signup and view all the answers

What is the purpose of the Update operation in a relational database?

<p>To modify attribute values in existing tuples. (C)</p> Signup and view all the answers

Which of the following combinations could lead to a violation of referential integrity?

<p>Updating a tuple's primary key to an invalid value. (D)</p> Signup and view all the answers

Flashcards

Domain

A set of possible values for an attribute in a relation.

Attribute

A named property or characteristic of an entity in a relation.

Relation Schema

A description of a relation, including its name and attributes.

Relation

A table that represents data.

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Data Type

Specifies the format of values allowed for an attribute.

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Employee_Ages (domain)

Possible employee ages (integers between 15 and 80).

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Degree/Arity

Number of attributes in a relation's schema.

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Usa_phone_numbers (domain)

Telephone numbers in the form (ddd)ddd-dddd, with valid area codes.

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Candidate Key

A key that uniquely identifies each tuple in a relation.

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Primary Key

The chosen candidate key used to uniquely identify tuples.

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Unique Key

A candidate key that is not the primary key.

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Key Determination

Determining a key based on attribute meaning and time-invariance.

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Time-invariant Attribute

An attribute that always holds true for a tuple

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Superkey

Set of attributes that uniquely identify tuples in a relation.

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Tuple

A row (record) in a table. Represents a specific instance in a relation.

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Referential Integrity Constraints

Rules that ensure relationships between tables are valid and consistent. Foreign keys are essential.

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Foreign Key (in relation to Referential Integrity)

An attribute in one relation that references a primary key in another relation, maintaining consistency between them.

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Foreign Key in EMPLOYEE relation

The attribute (e.g., Dno) in the EMPLOYEE relation that points to a department in DEPARTMENT relation.

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Self-Referencing Foreign Key

A foreign key that references the same relation.

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Super_ssn Attribute

A foreign key in EMPLOYEE relation referencing the supervisor in the same EMPLOYEE relation.

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NULL Value in Foreign Key

Indicates that a record may not be associated with a record related in another table.

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Database Relationship

The connection or link between different records.

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State Constraints

Rules defining constraints that a valid database state must satisfy.

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Transition Constraints

Rules that govern changes (transitions) in a database's state.

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Update Operations

Database operations that modify the data (insert, delete, update).

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Insert Operation

Adding new data rows to a table.

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Delete Operation

Removing data rows from a table.

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Update (Modify) Operation

Changing existing data in a table.

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Relational Algebra

Set of operations for retrieving data from a relational database.

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Integrity Constraints

Rules ensuring data in a database is valid and consistent.

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What is a relation state?

A set of tuples that conforms to a relation schema. It's essentially a snapshot of the data at a given time.

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What are NULL values?

They represent missing or unknown information in a tuple. It signifies a value is not applicable, known, or available.

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Why should NULL values be avoided?

NULLs can complicate data analysis and query processing, potentially leaving results ambiguous.

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What are schema-based constraints?

Rules explicitly defined in the database schema to ensure data integrity.

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What are semantic constraints?

These are business rules that are not directly enforced by the database schema but define the meaning and relationships of data.

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Referential Integrity

A constraint that ensures relationships between tables are consistent, preventing data inconsistencies. It dictates that a value in a referencing attribute (a foreign key) must match an existing value in the referenced attribute (a primary key).

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Referential Integrity Violation

Occurs when a value in a foreign key attribute does not match any existing value in the referenced primary key attribute. It breaks the relationship between tables.

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What are the three potential actions taken by a DBMS on a Referential Integrity violation?

  1. Restrict: Decline the action that would cause the violation.
  2. Cascade: Delete or update the referencing tuple(s) to maintain consistency.
  3. Set Null/Default: Change the referencing attribute value to NULL or a default value.
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Update Condition

A condition specified during the update operation that defines which tuple(s) to be targeted for modification. This condition is often based on attribute values.

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Valid Update

An update operation that does not violate any data constraints, including referential integrity.

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Invalid Update

An update operation that would violate a data constraint, such as referential integrity, resulting in an error.

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Update Operation Example

An example of the update operation would be changing an employee's salary. For example, "Update the salary of the EMPLOYEE tuple with Ssn = '999887777' to 28000." This would change the salary of a specific employee.

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Study Notes

Relational Data Model and Constraints

  • Relational databases were introduced by Ted Codd in 1970.
  • The model uses relations (tables) as its foundation.
  • The relational model has a theoretical basis in set theory and first-order predicate logic.
  • Early implementations appeared in the 1980s (e.g., SQL/DS, Oracle).
  • Popular commercial RDBMSs include DB2, Oracle, Sybase, SQL Server, Microsoft Access, MySQL, and PostgreSQL.
  • Many commercial and open source systems now implement relational models.

Relational Model Concepts

  • A domain is a set of atomic values represented by a data type (e.g., phone numbers, social security numbers).
  • An attribute is the name of a role played by a domain within a relation schema.
  • A tuple is an ordered list of attribute values, a row in the table.
  • The degree (arity) of a relation is the number of attributes in the relation schema.
  • A relation schema defines a relation (e.g., STUDENT (Name, SSN, Home_phone, Address...).
  • A relation state is the set of tuples in a given relation schema at a specific time.

Relational Model Constraints

  • Domain Constraints: Each value in a tuple must come from the appropriate domain (data type).
  • Key Constraints: A key of a relation schema is a minimum superkey (a set of attributes with unique values for each tuple).
  • Entity Integrity Constraint: Key values cannot be NULL.
  • Referential Integrity Constraint: A foreign key in one table must reference an existing primary key in another table.
  • NULL Values: Used to represent unknown or inapplicable values.

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Relational Data Model & Database Constraints PDF

Description

Explore the foundational concepts of the relational data model, introduced by Ted Codd in 1970. This quiz covers key elements such as domains, attributes, and relational databases. Test your knowledge on the early implementations and popular RDBMSs.

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