Database Relationships and Attributes Quiz
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Questions and Answers

What is a possible cardinality ratio for binary relationships?

  • 1:2
  • N:1 (correct)
  • 3:4
  • 2:3

A weak entity type does not have key attributes of its own.

True (A)

What are the two possible participation constraints?

Total and Partial

The cardinality ratio for a 'Works For' relationship between EMPLOYEE and DEPARTMENT is ____.

<p>N:1</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Cardinality Ratio = Specifies the maximum number of relationship instances Weak Entity Type = An entity lacking key attributes Strong Entity Type = An entity with key attributes Total Participation = Entity must be related to another entity</p> Signup and view all the answers

What type of attribute holds only one value?

<p>Single-valued attributes (C)</p> Signup and view all the answers

Derived attributes are the original attributes from which other attributes are computed.

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

What are the attributes called that can have multiple values?

<p>Multivalued attributes</p> Signup and view all the answers

A special attribute called ______ is created to represent unknown values.

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

Which of the following correctly describes key attributes?

<p>Attributes whose values are distinct for each entity (A)</p> Signup and view all the answers

Match the following types of attributes with their descriptions:

<p>Simple attributes = Attributes that are not divisible Composite attributes = Attributes made from multiple attributes Multivalued attributes = Attributes that can hold multiple values Stored attributes = Attributes from which derived attributes are computed</p> Signup and view all the answers

Composite attributes are represented by brackets.

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

What is an entity set?

<p>A collection of entities that share the same attributes.</p> Signup and view all the answers

What is the primary purpose of a value set (domain) in an entity set?

<p>To specify the set of values an attribute may hold (D)</p> Signup and view all the answers

The degree of a relationship type that involves three entity types is called binary.

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

What are the key attributes of the PROJECT entity type?

<p>Name and Number</p> Signup and view all the answers

A relationship type where the same entity type participates in different roles is known as a ______ relationship.

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

Which attribute is multivalued in the DEPARTMENT entity type?

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

Match the following entity types with their corresponding attributes:

<p>DEPARTMENT = Name, Number, Locations, Manager, ManagerStartDate PROJECT = Name, Number, Location, ControllingDepartment EMPLOYEE = Name, SSN, Sex, Address, Salary, BirthDate, Department, Supervisor DEPENDENT = Employee, DependentName, Sex, BirthDate, Relationship</p> Signup and view all the answers

ManagerStartDate is an attribute that is necessary for both Employee and Department.

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

What role does an EMPLOYEE play in the WORKS_FOR relationship?

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

What is the primary purpose of the Entity Relationship Model?

<p>To design and manage databases (B)</p> Signup and view all the answers

An employee may work on several projects that are controlled by the same department.

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

What type of information is kept track of for each employee in the example application?

<p>Name, social security number, address, salary, sex, and birthdate.</p> Signup and view all the answers

A department has a specific ______ who manages it.

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

Match the following attribute types with their definitions:

<p>Simple = Cannot be divided further Composite = Can be divided into smaller parts Single valued = Contains only one value per instance Multivalued = Can contain multiple values for a single entity</p> Signup and view all the answers

Which of the following statements is true regarding attributes?

<p>Attributes can be simple, composite, single valued, or multivalued. (B)</p> Signup and view all the answers

A unique number identifies each project in the example application.

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

Relationships in the E-R model describe how entities are ______.

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

Flashcards

Entity

A real-world object with independent existence, like a car, person, or company.

Attributes

Represent characteristics or properties of an entity, like a person's name, age, or address.

Composite Attribute

An attribute composed of smaller parts with independent meaning, like address being divided into street, city, etc..

ER Model (Entity-Relationship Model)

An easy-to-understand representation of data that uses entities, attributes, and relationships.

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Entity Set

A collection of entities of the same type, like a collection of all employees in your company or all books in a library.

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Key

A special attribute uniquely identifying an entity within an entity set, like a social security number for a person.

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Relationship

A connection between entities, indicating a relationship between them, like an "employee working on a project"

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Relationship Set

A collection of relationships of the same type, like all employees working on projects.

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Cardinality Ratio

The maximum number of relationship instances an entity can participate in. For example, a Department can have many Employees (N), but an Employee can only work for 1 Department (1).

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Cardinality Ratios for Binary Relationships

The cardinality ratio specifies how many entities can be related. Possible ratios include 1:1, 1:N, N:1, and M:N.

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Weak Entity Type

A weak entity type lacks its own key attribute and depends on a strong entity type for identification. The relationship is called identifying.

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Participation Constraint

Identifies if an entity's existence depends on a relationship with another entity. Consider 'total' and 'partial' participation.

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ER Diagram Naming Conventions

Use singular names for entity types, write names in uppercase and attribute names capitalized. Use lowercase for role names.

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Atomic Attribute

An attribute that cannot be broken down into smaller parts. It represents a fundamental characteristic of an entity.

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Single-Valued Attribute

An attribute that can hold only one value at a time. For example, an employee's age.

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Multivalued Attribute

An attribute that can hold multiple values simultaneously. For example, a car can have multiple colors.

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Derived Attribute

An attribute whose value is calculated or derived from other attributes. For example, an employee's age is derived from their birth date.

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Stored Attribute

An attribute that stores the raw data used to calculate a derived attribute. For example, an employee's birth date is stored, and their age is calculated.

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Null Value

A special value used to indicate that an attribute has no applicable value. For example, an employee might not have a fax number or email address.

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Complex Attribute

A complex attribute that combines both composite and multivalued attributes. It can represent multiple values within structured parts.

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Key Attribute

An attribute whose value is unique for each individual entity within a set of entities. It helps distinguish one entity from another.

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Value Set (Domain)

The set of possible values that an attribute can possess. This is like defining the types of data an attribute can store, such as integer, text, or boolean.

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Relationship Type

A relationship type is like a connection between two or more entities, showing how they interact with each other and how they are related. It's like a description of how they are linked.

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Degree of Relationship Type

The number of entities participating in a relationship. A binary relationship has two entities, while a ternary relationship has three entities.

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Role Name

An attribute that helps to describe the role of an participating entity in a relationship type. It clarifies the meaning of the relationship.

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Recursive Relationship

A relationship type where the same entity type participates in the relationship multiple times, but in different roles.

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Relationship as Attributes

A situation where an attribute is relevant and needed for both entities involved in a relationship. Think of an attribute that bridges the gap between two entities.

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Study Notes

Database Systems Design & Management Lecture 3

  • Lecture focused on data modeling using the Entity Relationship Model (ERM)
  • Overview of high-level conceptual data models for database design
  • Covered example database applications, entity types, entity sets, attributes, and keys
  • Explored relationship types, relationship sets, roles, and structural constraints
  • Discussed ER diagrams, naming conventions, and design issues

Example Database Application

  • Company organized into departments

  • Each department has a unique name and number, managed by an employee

  • Track start date of employee managing a department

  • Departments have multiple locations

  • Departments manage multiple projects, each with a unique name, number, and location

  • Employee data stored including name, social security number, address, salary, sex, and birthdate

  • Employees assigned to one department but can work on multiple projects (not necessarily controlled by the same department)

  • Track hours per week an employee works on each project

  • Track direct supervisor of each employee

  • Track employee dependents (name, sex, birthdate, relationship) for insurance purposes

Entity Types, Entity Sets, Attributes and Keys

  • ER model describes data using entities, attributes, and relationships
  • An entity is a "thing" with independent existence (physical or conceptual)
  • Entities have attributes that describe them (e.g., employee name, address)
  • Attributes can be simple (indivisible) or composite (divisible into smaller parts)
  • Attributes can be single-valued (one value) or multi-valued (multiple values)
  • Attributes may be stored or derived
  • Attributes may hold null values if no applicable value exists
  • Composite attributes are enclosed in parenthesis
  • Multi-valued attributes enclosed in curly braces
  • Attributes with unique values are called key attributes
  • Value sets (domains) specify permissible values for attributes (e.g., integer, boolean)

Entity Types, Entity Sets

  • Databases usually contain similar entities grouped into entity types
  • Entity types are similar with same attributes
  • An collection of all entities of a particular entity type at any time is called an entity set
  • Entity type represented as a rectangle in ER diagrams

Attributes (continued)

  • Entity types have attributes, which are properties describing them
  • Attributes are named , and assigned to an entity type
  • Attributes may be simple or composite
  • Attributes may be single-valued or multi-valued
  • Attributes may be stored or derived
  • Attributes may have null values if no applicable value exists

Relationships, Relationship types, Roles & participation constraints, Cardinality ratios, key attributes

  • Relationships between entities
  • Degree of relationship - number of participating entity types (binary, ternary relationships)
  • Role names clarify the relationships
  • Recursive relationships
  • Cardinality ratios (max number of relationship instances)
    • 1:1, 1:N, N:1, M:N
  • Participation constraints (existence of one entity dependent on the other)
    • Total, Partial
  • Weak entity types do not have key attributes; dependent on other (strong) entities / relationships
  • ER diagrams, Naming conventions
    • Symbols for entities, attributes, relationships, etc
    • Naming conventions for entities, relationships, attributes
  • Initial Conceptual design of company database examples (Department, Project, Employee, Dependent)

Proper Naming of Schema Constructs

  • Use singular names for entity types
  • Entity type names and relationship types written in uppercase
  • Attribute names capitalized
  • Role names written in lower case

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Description

Test your knowledge on the cardinality ratios and participation constraints in binary relationships within database systems. Understand the concepts of entity sets, key attributes, and various types of attributes including composite and derived attributes. This quiz will challenge your understanding of fundamental database principles.

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