DATA MODELLING
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Questions and Answers

Which of the following statements accurately describes an entity in an entity relationship diagram (ERD)?

  • It is defined by its relationships with other entities.
  • It does not require a primary key.
  • It can exist independently of other entities. (correct)
  • It is always represented as a double rectangle.

What distinguishes a weak entity from a strong entity?

  • A weak entity is always a composite attribute.
  • A weak entity depends on a strong entity. (correct)
  • A weak entity has a primary key.
  • A weak entity cannot have relationships.

Which type of attribute can have multiple values associated with it?

  • Multivalued Attribute (correct)
  • Key Attribute
  • Derived Attribute
  • Composite Attribute

Which of the following correctly defines a composite attribute?

<p>An attribute that can be broken down into smaller sub-attributes. (A)</p> Signup and view all the answers

In the context of attributes, what does a foreign key represent?

<p>It references a primary key in another table. (D)</p> Signup and view all the answers

What type of attribute would 'Age' be classified as if it is derived from 'BornDate'?

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

Which of the following best describes a primary key in a relational database?

<p>An attribute that uniquely identifies each record in a table. (C)</p> Signup and view all the answers

Which of the following correctly represents a one-many relationship in a relational database schema?

<p>CREATE TABLE Student (StudentID, Name, Age, Email, PhoneNum ); CREATE TABLE Subject (SubjectID, Subject_name, Subject_time, StudentID ); (D)</p> Signup and view all the answers

What is the primary key in the following schema: CREATE TABLE Student (StudentID, Name, Age, Email, PhoneNum );

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

In a many-one relationship schema, which table would contain the foreign key referencing the other?

<p>Assign table referencing the Group table (B)</p> Signup and view all the answers

In the context of a relational database schema, what does the syntax 'CREATE TABLE Table_name (list of Attribute);' signify?

<p>It defines a structure for the entities to be stored. (D)</p> Signup and view all the answers

Which of the following configurations would represent a many-many relationship in a relational database?

<p>CREATE TABLE Student (StudentID, Name); CREATE TABLE Subject (SubjectID, Subject_name, Subject_time ); CREATE TABLE Enrollment (StudentID, SubjectID ); (C)</p> Signup and view all the answers

What describes a one-to-many relationship?

<p>One element of an entity is linked to many elements of another entity. (D)</p> Signup and view all the answers

Which of the following best exemplifies a many-to-many relationship?

<p>A student enrolled in multiple subjects. (B)</p> Signup and view all the answers

What is the cardinality of the relationship between students and assignments?

<p>M:N (B)</p> Signup and view all the answers

In which scenario would a one-to-one relationship be applicable?

<p>An employee receiving a salary once a month. (C)</p> Signup and view all the answers

What does a many-to-one relationship indicate?

<p>Several elements of one entity relate to a single element of another entity. (C)</p> Signup and view all the answers

Which phrase accurately defines cardinality in the context of relationships?

<p>The specific number of relationships that one entity can have. (B)</p> Signup and view all the answers

Which of these examples does NOT illustrate a many-to-many relationship?

<p>A child having one parent. (D)</p> Signup and view all the answers

What best represents a one-to-one relationship in a real-world scenario?

<p>A traveler using one passport. (C)</p> Signup and view all the answers

Which of the following statements is true regarding a one-to-many relationship?

<p>One lecturer can teach multiple students. (A)</p> Signup and view all the answers

Which statement best describes the concept of relationships in relational databases?

<p>Relationships dictate the structure of data stored within a database. (D)</p> Signup and view all the answers

Flashcards

Entity Relationship Diagram (ERD)

A graphical representation of data entities, their attributes, and relationships between them.

Entity

A fundamental building block of an ERD, representing a distinct object or concept in the data model.

Attribute

A characteristic or property of an entity.

Relationship

An association between two or more entities, indicating how they are related.

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Key Attribute

An attribute that uniquely identifies each instance of an entity, like a student ID number.

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Multivalued Attribute

An attribute that can hold multiple values for a single instance of an entity, like a student's phone numbers.

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Derived Attribute

An attribute whose value is derived from other attributes, like a student's age calculated from their birth date.

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Cardinality

The possible number of occurrences of an entity in a relationship.

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One-to-One Relationship

One entity can be linked to only one entity on the other side of the relationship.

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One-to-Many Relationship

One entity can be linked to multiple entities on the other side of the relationship.

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Many-to-One Relationship

Multiple entities can be linked to only one entity on the other side of the relationship.

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Many-to-Many Relationship

Multiple entities can be linked to multiple entities on the other side of the relationship.

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Database Schema

A database schema is a structured representation of data in a database. It describes the data types, relationships, and constraints of the database.

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Translating Conceptual ERD

A process of translating the conceptual ERD into a relational database model using tables, rows, and columns.

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Relational Database

A database model that uses tables to represent an entity and rows and columns to represent an attribute.

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Relational Schema

Describes the structure and organization of a relational database, showing tables, columns, relationships, and constraints.

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Primary Key

A special attribute uniquely identifying each record in a table. It helps to maintain data integrity and prevent duplicate entries.

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Foreign Key

A key attribute in one table that refers to the primary key in another table. It establishes a link between related tables, enforcing data consistency.

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Study Notes

Data Modeling Introduction

  • Data is represented using Entity-Relationship Diagrams (ERD).
  • Common data manipulation language includes CRUD (create, read, update, delete).
  • ERDs are frequently used in relational databases.

Entity-Relationship Diagram (ERD)

  • Entity: An object or component of data (represented in rectangles). Entities are independent and complete in themselves, not dependent on other entities. They have a primary key.
  • Attributes: Characteristics of the entity or relationship (represented in ellipses/ovals).
  • Relationships: Associations between two or more entities.

Entity Types

  • Strong Entity: Represented in a rectangle. Independent and complete. Holds its own primary key.
  • Weak Entity: Represented in a double rectangle. Dependent on another (strong) entity for its identity. Does not have a primary key.

Attributes Types

  • Key Attribute: Uniquely identifies an individual record (data pointer). Includes primary keys (underlined) and foreign keys (dash underlined), which refer to primary keys in other tables.
  • Multivalued Attribute: Relates to foreign keys, can hold multiple values.
  • Derived Attribute: Value derived from another attribute (e.g., age derived from birthdate).
  • Composite Attribute: A combination of multiple attributes (e.g., full name composed of first name and last name).

Relationships (Cardinality)

  • Relationship Types:
    • One-to-one (1:1): One element of an entity is linked to only one element of another entity (e.g., student to transport, one capital per nation).
    • One-to-many (1:N): One element links to more than one element of another entity. (e.g., student to subject).
    • Many-to-one (N:1): Many elements of an entity are linked to only one element of another entity (e.g., student to group).
    • Many-to-many (M:N): Many elements in one entity are linked to many elements in another entity (e.g., student to assignments).

Relational Database Schema

  • Conceptual ERDs need conversion into relational schema for database systems.
  • Syntax for creating relational tables using SQL is provided (CREATE TABLE).

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