E-R Modeling in Database Design
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Questions and Answers

What is a candidate key?

  • A key that identifies a class of objects uniquely.
  • A super key from which extraneous attributes have been removed. (correct)
  • Any key that is chosen as the primary key.
  • A key containing all attributes of an entity.

    • What defines a weak entity?

  • An entity that can be uniquely identified by its own attributes.
  • An entity dependent on another entity for its identification. (correct)
  • An entity that has a super key.
  • An entity that can exist independently.

    • In an ER diagram, what does 'ISA' represent?

  • A mapping cardinality relationship.
  • A hierarchy depicting generalization and specialization. (correct)
  • Employee associated with a customer.
  • An identification method for weak entities.

    • Which of the following mapping cardinalities describes a relationship where one entity in E1 could relate to multiple entities in E2?

    <p>One to many (A)</p> Signup and view all the answers

    What characterizes a primary key?

    <p>It is chosen from candidate keys for the database implementation. (D)</p> Signup and view all the answers

    What indicates that an entity set does not have a super key?

    <p>It cannot be uniquely identified by its attributes. (D)</p> Signup and view all the answers

    In a many to many relationship, how many entities can be related?

    <p>Any number of entities from both sides can be related. (C)</p> Signup and view all the answers

    What is the purpose of the Entity-Relationship model?

    <p>To represent a logical design of a database (C)</p> Signup and view all the answers

    What defines an entity set?

    <p>A collection of all similar entities (C)</p> Signup and view all the answers

    What is the role of an ER diagram in database design?

    <p>It captures possible entity sets, attributes, and relationships. (A)</p> Signup and view all the answers

    Which of the following correctly describes attributes?

    <p>They are characteristics describing any entity (A)</p> Signup and view all the answers

    What is a super key?

    <p>One or more attributes that help uniquely identify an entity (A)</p> Signup and view all the answers

    In the example given, what is the relationship between 'Student' and 'School'?

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

    Which relationship set is represented by the connection between a job and a database?

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

    Which of the following statements about candidate keys is true?

    <p>They are a minimal subset of a super key (B)</p> Signup and view all the answers

    What can be true about attributes of an entity?

    <p>An entity can be described by zero or more attributes (A)</p> Signup and view all the answers

    Flashcards

    Entity Set

    A group of similar entities.

    Entity

    A real-world object or concept.

    Attribute

    A characteristic of an entity.

    Relationship

    Association among entities.

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    Super Key

    Attributes that uniquely identify an entity.

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    Candidate Key

    Smallest part of Super Key that uniquely identifies.

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    ER Diagram

    A visual way to show database structure using entities and relationships.

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    E-R Modeling

    Conceptual design of databases using entities and relationships.

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    Weak Entity

    An entity that depends on another entity for its existence and cannot be uniquely identified by its own attributes.

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    Prime Attribute

    An attribute that is part of any super key, meaning it contributes to uniquely identifying an entity.

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    Primary Key

    A candidate key chosen to be the unique identifier for an entity in a database.

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    What is Entity Generalization?

    Combining multiple entity sets with similar characteristics into a more general entity type.

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    What is Entity Specialization?

    Breaking down a general entity type into more specific subtypes with additional characteristics.

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    One-to-Many Mapping

    A relationship where one entity in the first set can relate to multiple entities in the second set, but each entity in the second set can only relate to one entity in the first set.

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    Many-to-Many Mapping

    A relationship where any number of entities in either set can relate to any number of entities in the other set.

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    Study Notes

    E-R Modeling from Problem Statements

    • E-R modeling is a crucial step in database design.
    • It provides a conceptual/logical model of the database before creating specific database tables and relationships.
    • This process uses Entity-Relationship diagrams.

    Introduction

    • Developing databases is a critical task in system development.
    • Before creating database tables and defining relationships, E-R diagrams provide a logical representation.
    • This study will demonstrate identifying entities and defining relationships.

    Objectives

    • After completing this lesson, students will be able to:
      • Identify entity sets, their attributes, and relationships.
      • Create a data model using an E-R diagram.

    Entity Relationship Model

    • The Entity-Relationship model is used for designing databases.
    • It represents real-world objects as entities.
    • Relationships between these objects are crucial and modeled as well.
    • Examples: Student and School are entities, related by "Studies in" relationship; Job and Database - related by "Updates" relationship.

    Entity Set and Relationship Set

    • An entity set is a collection of similar entities.
    • Examples: Student, School.
    • A relationship set is a collection of similar relationships.
    • Entities like Ram and John are specific entities within the Student entity set.

    Attributes of Entities

    • Attributes describe the characteristics of an entity.
    • Entities can have zero or more attributes.
    • Example: A student has attributes like name, age, address, roll number, and grade.

    Keys

    • Keys are used to uniquely identify entities.
    • A super key is a set of attributes that uniquely identifies an entity within a set.
    • Examples: School grade and roll number uniquely identify a student.
    • A candidate key is a minimal super key; removing any attribute from it would no longer allow unique identification.
    • The primary key is the candidate key chosen for a particular database implementation.
    • Prime attribute: Any attribute that is part of a super key.

    Weak Entity

    • A weak entity is dependent on another entity for its identification.
    • It cannot be uniquely identified by its attributes alone.
    • For example, a family needs the employee to exist.

    Entity Generalization and Specialization

    • Entities can have similarities or be specialized (e.g., customers and employees are forms of people).
    • Entity models often use ISA hierarchies to display these specializations and generalizations.

    Mapping Cardinalities

    • Mapping cardinalities define relationships between entities.
    • The relationship can be:
      • One-to-one (one entity from set A to one entity from set B)
      • One-to-many (one entity from set A to many entities from set B)
      • Many-to-one (many entities from set A to one entity from set B)
      • Many-to-many (many entities from set A to many entities from set B).

    ER Diagram

    • An ER diagram is a pictorial representation of entities, attributes, and relationships.
    • The diagram uses specific notations to represent different elements.

    Graphical Notations for ER Diagram

    • The study notes include examples highlighting graphical elements (rectangles, ellipses, diamonds, etc.) and how to denote them in diagrams
    • These elements denote specific elements of the diagram (entities, attributes, relationships).

    Importance of ER Modeling

    • The first step in relational database implementation is defining an ER diagram.
    • ER diagrams are crucial because they ensure efficient and accurate data storage and maintenance by identifying and visualizing data relationships in a problem statement.
    • Normalizing tables in order to remove redundant data is also a significant stage following the ER diagram creation.

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    Related Documents

    E-R Modeling from the Problem Statements PDF

    Description

    This quiz focuses on E-R modeling, an essential step in database design. Students will learn to identify entities, their attributes, and relationships, as well as create data models using E-R diagrams. Mastery of these concepts is crucial for effective database development.

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