Mapping ER Diagrams to Relational Databases
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Mapping ER Diagrams to Relational Databases

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Questions and Answers

What is the primary key of the weak entity 'Dependent' as stated in the context?

  • Dlast_name
  • Birth_date
  • Dfirst_name (correct)
  • Employee_id

    • In a binary M:N relationship, how is the new table structured?

  • By mapping the primary key of the first entity only.
  • With the foreign key of both entities as a single composite key. (correct)
  • Creating a unique key that incorporates timestamps of each entry.
  • Using random attributes from both entities as keys.

    • What is the role of the primary key from the owner entity in relation to a weak entity?

  • It serves as the primary key of the weak entity table.
  • It acts as a foreign key in the weak entity table. (correct)
  • It is ignored in weak entity relationships.
  • It becomes a unique index for the weak entity.

    • For a binary 1:1 relationship, how should the foreign keys be configured?

    <p>The primary key of Entity A is included in Entity B.</p> Signup and view all the answers

    What information does the weak entity 'Dependent' primarily rely on from its owner entity?

    <p>The foreign key reference from the Employee entity.</p> Signup and view all the answers

    To accurately establish entities in a relational database, which of the following must be true regarding weak entities?

    <p>Their existence is dependent on the owner entity's primary key.</p> Signup and view all the answers

    What does the 'Enroll' table in the context represent?

    <p>A mapping of students to courses they are enrolled in.</p> Signup and view all the answers

    In the context of mapping entities, which attribute must the 'Course' entity possess?

    <p>A credit hours column.</p> Signup and view all the answers

    What does the PK/FK method achieve in mapping binary 1:N relationships?

    <p>It ensures each entry in the child table can only link to one entry in the parent table.</p> Signup and view all the answers

    Which mapping rule is utilized for 1:N recursive relationships?

    <p>Keep the primary key in the same table along with the recursive key.</p> Signup and view all the answers

    In the context of the provided content, what does a recursive relationship imply?

    <p>An entity can relate to itself in a parent-child format.</p> Signup and view all the answers

    What is a characteristic feature of M:N recursive relationships as mentioned in the content?

    <p>They require the creation of a separate table to manage the relationship.</p> Signup and view all the answers

    When mapping the Student and Car relationship, what type of relationship is being established?

    <p>1:N relationship where a student can own multiple cars.</p> Signup and view all the answers

    What is the purpose of mapping binary relationships?

    <p>To clarify the connections between different entities in a data model.</p> Signup and view all the answers

    In a scenario where multiple employees report to the same manager, which mapping would correctly represent this relationship?

    <p>A 1:N mapping with one manager linked to many employees.</p> Signup and view all the answers

    What is a potential drawback of using the PK/FK method for mapping relationships?

    <p>It may complicate the design of the database schema.</p> Signup and view all the answers

    What should be done when mapping multiple candidate keys for a strong entity in a relational database?

    <p>Choose one candidate key as the primary key.</p> Signup and view all the answers

    How should multi-valued attributes be handled in the mapping process?

    <p>Create a separate table for the multi-valued attribute.</p> Signup and view all the answers

    Which attribute types require different mapping strategies when forming tables?

    <p>Atomic, composite, and multi-valued attributes.</p> Signup and view all the answers

    What is the primary key in the table created for multi-valued attributes?

    <p>The original table's primary key as a foreign key.</p> Signup and view all the answers

    In the mapping of weak entities, what is the first step to take?

    <p>Create a new table and include a foreign key related to a strong entity.</p> Signup and view all the answers

    How should attributes for a composite entity be formed when mapping?

    <p>By forming columns from the elementary (atomic) parts of the composite.</p> Signup and view all the answers

    Which of the following best describes the mapping of relationships in relational databases?

    <p>Different types of relationships such as M:N, 1:1, and 1:N require different mapping techniques.</p> Signup and view all the answers

    Which of the following is true regarding strong entities in a relational database?

    <p>They are represented as separate tables with their indicated keys as primary keys.</p> Signup and view all the answers

    Study Notes

    Lecture 1: Mapping ER Diagram to a Relational Database

    • The lecture covers mapping Entity-Relationship (ER) diagrams to relational databases.
    • The outline includes mapping strong entities, weak entities, different types of relationships (M:N, 1:1, 1:N, recursive, n-ary), and generalizations/specializations.

    Mapping Strong Entities (M1)

    • For strong entities, create a new table for each entity.
    • The indicated key of the strong entity becomes the primary key of the table.
    • Choose one candidate key as the primary key if multiple exist.
    • Attributes can be atomic, composite, or multi-valued.

    Atomic Attributes (M1.A)

    • Atomic attributes are mapped to columns in the table.

    Composite Attributes (M1.B)

    • Composite attributes are broken down into their atomic components, each becoming a separate column in the table.

    Multi-valued Attributes (M1.C)

    • Create a separate table for multi-valued attributes.
    • The primary key from the original table becomes a foreign key in the new table.
    • The key of the new table is the primary key.

    Mapping Weak Entities (M2)

    • Create a new table for each weak entity.
    • Use the same steps as in M1.
    • Include the primary key of the owner entity as a foreign key in the weak entity table.
    • The primary key of the weak entity table is a partial key.

    Mapping Binary M:N Relationships (M3)

    • For M:N relationships, create a new table.
    • The primary keys from both entities become the combined primary key in the new table.

    Mapping Binary 1:1 Relationships (M4)

    • For 1:1 relationships, include the primary key of the first entity into the second entity as a foreign key.

    Mapping Binary 1:N Relationships (M5)

    • Most 1:N relationships are mapped using the primary key/foreign key method.
    • A separate table can also be used for this.

    Mapping Recursive Relationships (M6)

    • For 1:N recursive relationships, the primary key of the table is re-included in the table.
    • For M:N recursive relationships, a separate table is created.

    Mapping n-ary Relationships (M7)

    • For n-ary relationships, create a table including all attributes of the relationship.
    • Include the keys from all connected entities as foreign keys.
    • Concatenate the foreign keys to form the primary key.

    Mapping Generalizations/Specializations (M8)

    • Create a table for the generalization entity and a table for each specialization entity.
    • Put attributes in corresponding columns.
    • Include the primary key of the generalization entity in the specialization entity tables.

    Summary of Mapping Constructs and Constraints (Table 1)

    • Provides a correspondence between ER model and relational model elements.
    • Lists the equivalent constructs in both models: entities, relationships, attributes, etc.

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    Lecture 1: Mapping ER Diagram to Relational Database PDF

    Description

    This quiz covers the principles of mapping Entity-Relationship diagrams to relational databases. It focuses on defining strong entities, weak entities, and various relationship types while explaining how to handle different attribute types including atomic, composite, and multi-valued attributes.

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