Mapping ER Diagrams to Relational Databases

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Questions and Answers

What role does the primary key of the owner entity play in a weak entity relationship?

  • It serves as a unique identifier for all entities.
  • It is included as a foreign key in the weak entity table. (correct)
  • It is not necessary for the weak entity relationship.
  • It becomes the primary key of the weak entity.

In the mapping of binary M:N relationships, what is the key of the new table created?

  • The key of the new table is the total number of students.
  • The primary key of the new table is the maximum credit hours.
  • The key of the new table is the course name.
  • The key of the new table is the concatenated keys of the two owner entities. (correct)

Which attribute defines a weak entity's primary key in the given example?

  • Last_name
  • Dependent_name
  • First_name (correct)
  • Employee_id

What is the foreign key in the Dependent entity table in this context?

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

In a binary 1:1 relationship, what should be done to relate the two entities?

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

Which of the following statements is true regarding the Employee and Dependent relationship?

<p>Each employee can have multiple dependents. (C)</p> Signup and view all the answers

How is the relationship between Course and Student entities defined in a mapping of binary M:N relationships?

<p>A student can enroll in multiple courses, and each course can have multiple students. (B)</p> Signup and view all the answers

What components make up a primary key in a weak entity?

<p>A partial key combined with the owner's primary key. (D)</p> Signup and view all the answers

What is the primary key (PK) in the student table?

<p>Student_id (D)</p> Signup and view all the answers

Which of the following relationships is typically represented with a foreign key (FK) in a database?

<p>1:N relationships (C)</p> Signup and view all the answers

In the case of a recursive 1:N relationship, what should be included in the same table?

<p>The primary key of the table (A)</p> Signup and view all the answers

How should M:N recursive relationships be mapped in a database?

<p>With a separate table for the relationship (C)</p> Signup and view all the answers

Which statement correctly describes the function of foreign keys in the context of binary relationships?

<p>They serve as identifiers for primary keys in other tables (A)</p> Signup and view all the answers

What characterizes a 1:N mapping in entity relationships?

<p>Multiple entities can relate back to one entity (B), One entity can relate to multiple entities (C)</p> Signup and view all the answers

What determines the choice between using a separate table and using PK/FK mapping for entity relationships?

<p>The necessity for additional attributes in the relationship (A)</p> Signup and view all the answers

In the example of an employee managing another employee, what does the 'Manage_id' represent?

<p>The identifier of the manager employee (A)</p> Signup and view all the answers

What is the correct method to map strong entities with atomic attributes?

<p>Form columns from the atomic attributes in a new table. (D)</p> Signup and view all the answers

What should be done for entities with composite attributes when mapping to a relational database?

<p>Form columns from the elementary parts of the composite attributes. (D)</p> Signup and view all the answers

How should multi-valued attributes be handled when mapping to a relational database?

<p>Placed in a separate table with the original table's primary key as a foreign key. (D)</p> Signup and view all the answers

What is required when mapping weak entities?

<p>A new table is created for each weak entity. (B)</p> Signup and view all the answers

Which of the following statements about primary keys is true when mapping strong entities?

<p>The indicated key of the strong entity becomes the primary key of the new table. (A)</p> Signup and view all the answers

What is the primary characteristic of atomic attributes?

<p>They cannot be divided and represent a single piece of data. (C)</p> Signup and view all the answers

When dealing with binary M:N relationships, what is a common approach in mapping?

<p>A junction table is created to link the two entities. (B)</p> Signup and view all the answers

Which attribute type requires creating a new table solely for that attribute during mapping?

<p>Multi-valued attributes (D)</p> Signup and view all the answers

Flashcards

Strong Entity Mapping

Create a new table for each strong entity, using the entity's key as the table's primary key.

Atomic Attribute

A single, indivisible data value (like an integer or string).

Composite Attribute

An attribute composed of multiple atomic attributes.

Multi-valued Attribute

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

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Primary Key

A unique identifier for each row in a table.

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Foreign Key

A column in one table that refers to the primary key of another table.

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Weak Entity Mapping

Create a new table for each weak entity, following similar steps as for strong entities.

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Weak Entity Relationship

A weak entity is dependent on another entity (strong entity) for its existence. It cannot exist without its owner.

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Owner Entity

The entity that a weak entity depends on for its existence.

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Partial Key

The primary key of a weak entity, composed in part from the key of the owner entity.

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Foreign Key in Weak Entity

The primary key of the owner entity included as a foreign key in the weak entity table.

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M:N Relationship

A relationship where multiple instances of one entity can be related to multiple instances of another entity.

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New Table for M:N

Create a new dedicated table to represent the relationship between two entities in an M:N relationship. This table combines both primary keys as its primary key.

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1:1 Relationship

A relationship where one instance of an entity can only be linked to one instance of another entity and vise versa.

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Foreign Key in 1:1 Relationship

The primary key of one entity is included as a foreign key in the other entity table.

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1:N relationship

A relationship between two entities where one entity can have multiple related entities, but each related entity can only have one corresponding entity in the parent entity.

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PK/FK method

A method to map 1:N relationships in a database. The primary key (PK) of the parent table is included as a foreign key (FK) in the child table.

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Primary Key (PK)

A unique identifier for each record in a table. No two rows can have the same PK value.

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Foreign Key (FK)

A field in a child table that refers to the primary key of the parent table.

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Recursive relationship

A relationship between entities of the same type.

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1:N recursive relationship mapping

In a 1:N recursive relationship, the primary key of the table participating in the recursive relationship is repeated in the same table.

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M:N recursive relationship mapping

For M:N recursive relationships, a separate table is created to represent the relationship.

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Study Notes

Lecture 1: Mapping ER Diagram to a Relational Database

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

M1. Map Strong Entities

  • Create a new table for each strong entity.
  • Use the entity's primary key as the table's primary key.
  • Choose one candidate key if multiple exist.
  • Attributes are categorized as: atomic, composite, and multi-valued.

M1.A. Atomic Attributes

  • Create a column for each atomic attribute in the table.

M1.B. Composite Attributes

  • Create columns from the elementary parts of the composite attribute.

M1.C. Multi-valued Attributes

  • Create a separate table for the multi-valued attribute.
  • Include the primary key from the original table as a foreign key.
  • The new table's key is the primary key.

M2. Map Weak Entities

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

M3. Map Binary M:N Relationships

  • Create a new table for each M:N relationship.
  • Include the primary keys of both entities as foreign keys.
  • The concatenated foreign keys of both entities represent the primary key in the new table.

M4. Map Binary 1:1 Relationships

  • Include the primary key of entity A as a foreign key into entity B (the relationship).

M5. Map Binary 1:N Relationships

  • Most 1:N relationships are mapped using the primary-key/foreign-key method.
  • A separate table can also be created following M3 rules.

M6. Map Recursive Relationships

  • For 1:N recursive relationships, re-include the primary key of the table into the same table to establish the recursive relationship.
  • For M:N recursive relationships, create a separate table for the relationship.

M7. Map n-ary Relationships

  • Create a new table for each n-ary relationship.
  • Include all attributes of the relationship in the table.
  • Use the keys of the connected entities as foreign keys, combining them for the primary key of the new table.

M8. Map Generalizations/Specializations

  • Create one table for the generalization entity and one for each specialization entity.

  • Place attributes for each entity in its corresponding table.

  • Include the primary key of the generalization entity in the specialization entity table.

  • This is an example of an ERD:

    • A person can be an employee or a customer.
    • An employee can be an officer, teller, or secretary.
    • Each has specific attributes.

Summary of Mapping Constructs and Constraints

  • This table summarizes the correspondence between ER and relational models.
    • ER model elements (entity type, relationship type, attributes) and their relational model counterparts (Entity relation, foreign key, attribute, relationship relation) are listed.

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Lecture 1: Mapping ER Diagram to Relational Database PDF

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