Database Systems Quiz

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Questions and Answers

What is the correct terminology for the components of a relation?

  • Entity, instance, value
  • Table, row, column
  • Relation, tuple, attribute (correct)
  • Set, element, property

What is a key characteristic of a relation in a database?

  • Tuples are distinct; there are no duplicates (correct)
  • The order of attributes has significance
  • Tuples can have duplicate values
  • Attributes can have duplicate names

What is a super key in the context of database systems?

  • A set of attributes that uniquely identifies a tuple within a relation (correct)
  • The primary key of a relation
  • An attribute that uniquely identifies a relation
  • A foreign key referencing another relation

What is true about a candidate key in a database system?

<p>It is a super key with no proper subset being a super key (D)</p> Signup and view all the answers

What is a composite key in a database system?

<p>A key consisting of more than one attribute (D)</p> Signup and view all the answers

What does a foreign key represent in a database system?

<p>An attribute that matches the primary key of another relation (D)</p> Signup and view all the answers

What does the entity integrity constraint state in a database system?

<p>No attribute of a primary key can be null (A)</p> Signup and view all the answers

What is a base relation in a database system?

<p>A named relation stored in the database (B)</p> Signup and view all the answers

What represents a physically stored relation in the database?

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

What is represented by an entity type in the ER model?

<p>A relationship between objects (B)</p> Signup and view all the answers

What is a relationship type in the ER model?

<p>A set of meaningful associations among entity types (B)</p> Signup and view all the answers

What is an attribute in the ER model?

<p>A property of an entity or a relationship type (A)</p> Signup and view all the answers

What is the difference between a composite attribute and a simple attribute?

<p>Composite attributes can be divided into smaller subparts; simple attributes cannot (B)</p> Signup and view all the answers

What is a multivalued attribute?

<p>An attribute that can have multiple values for each entity (C)</p> Signup and view all the answers

What is a derived attribute?

<p>An attribute that is calculated from other attributes (D)</p> Signup and view all the answers

What does a value set or domain represent for an attribute?

<p>The set of all possible values for an attribute (C)</p> Signup and view all the answers

Flashcards

Relation components

Relation, tuple, and attribute.

Key relation characteristic

All tuples (rows) are distinct; no duplicates are allowed.

Super key

A set of attributes that uniquely identifies each tuple (row) in a relation (table).

Candidate key

A super key where no subset of its attributes is also a super key (minimal super key).

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Composite key

A key that consists of two or more attributes combined to uniquely identify a tuple.

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Foreign key

An attribute in one relation that refers to the primary key of another relation.

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Entity integrity constraint

No attribute of a primary key can contain a null value.

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Base Relation

A relation that is physically stored in the database.

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Relation (physical)

A named relation stored in the database.

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Entity Type

A collection of entities that share common properties.

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Relationship type

A set of meaningful associations among two or more entity types.

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Attribute (ER Model)

A property or characteristic of an entity or relationship.

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Composite vs. Simple Attribute

Composite attributes can be divided; simple attributes cannot.

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Multivalued attribute

An attribute that can hold multiple values for a single entity.

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Derived attribute

An attribute calculated from other attributes; it's not directly stored.

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Value set / Domain

The set of all possible values an attribute can hold.

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Study Notes

Database Systems: Components and Terminology

  • A relation consists of tuples (rows) and attributes (columns)
  • Correct terminology: relation, tuple, attribute
  • Attributes can have distinct names, but no duplicates

Properties of Relations

  • Each cell contains exactly one atomic value
  • Tuples are distinct, no duplicates
  • The order of attributes has no significance

Keys

  • A super key is a set of attributes that uniquely identifies a tuple within a relation
  • A candidate key is a super key with no proper subset being a super key
  • A primary key is a selected candidate key for each relation
  • A composite key consists of more than one attribute

Foreign Keys

  • A foreign key represents an attribute that matches the primary key of another relation
  • Foreign keys must match a candidate key value or be null

Entity Integrity Constraint

  • No attribute of a primary key can be null

Base Relations and Views

  • A base relation is a named relation stored in the database
  • A view is a dynamic result of relational operations on base relations

ER Model: Entity Types, Relationships, and Attributes

  • An entity type represents a group of objects with the same properties
  • A relationship type represents a set of meaningful associations among entity types
  • An attribute is a property of an entity or a relationship type

Attributes in ER Model

  • A composite attribute can be divided into smaller subparts
  • A multivalued attribute can have multiple values for each entity
  • A derived attribute is calculated from other attributes
  • A value set or domain represents the set of all possible values for an attribute

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