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. (D)</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. (C)</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. (D)</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. (D)</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. (D)</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. (C)</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. (A)</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. (C)</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. (A)</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. (B)</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. (B)</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. (D)</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. (C)</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. (D)</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. (B)</p> Signup and view all the answers

Which attribute types require different mapping strategies when forming tables?

<p>Atomic, composite, and multi-valued attributes. (B)</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. (D)</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. (A)</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. (C)</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. (C)</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. (A)</p> Signup and view all the answers

Flashcards

Strong Entity Mapping

A strong entity is mapped into a new table, using the entity's key attribute as the table's primary key.

Atomic Attribute

Atomic Attribute is a basic data type attribute. It cannot be further divided into sub-parts.

Composite Attribute

Composite Attribute is an attribute with multiple parts. Each part is an atomic attribute, and these are mapped into columns in the table.

Multi-valued Attribute

A Multi-valued Attribute is an attribute that can have multiple values.

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Primary Key

Primary key is unique identifier for each row in a table.

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Foreign Key

Foreign key is a field (or set of fields) in one table that refers to the primary key of another table.

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Weak Entity Mapping

Weak entities are mapped to a new table in a relational database, with similar steps as strong entities.

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Weak Entity Mapping

Weak entities are linked to their owner entity by including the owner's primary key as a foreign key in the weak entity table.

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Foreign Key

A field in a table that references the primary key of another table, establishing a link between tables.

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Primary Key

A unique identifier for each record (row) within a table.

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Partial Key

Used as the primary key for a weak entity; it's a combination of attributes.

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1:N Relationship (Mapping)

One record in the first table maps to zero or more records in the second table.

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M:N Relationship (Mapping)

Creating a new table for many-to-many relationships, combining primary keys from each original table

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1:1 Relationship (Mapping)

One record in each of two tables is linked by replicating the primary key of one table in the other as a foreign key.

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1:N Relationship Mapping

A binary relationship where one record in a table can relate to multiple records in another table. It's often mapped using a primary key (PK) and a foreign key (FK).

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PK/FK Method

A common way to map 1:N relationships in relational databases. The foreign key in the related table references the primary key in the first table.

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Separate Table Mapping

An alternative method to map 1:N relationships by creating a separate table for the related entities.

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Recursive Relationship (1:N)

A relationship where an entity relates to itself, with one record in the table potentially related to multiple different records within the same table (in a hierarchical/managerial context.)

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Recursive Relationship (M:N)

When an entity can be related to multiple other entities of the same type (many-to-many).

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Foreign Key (FK)

A field (or set of fields) in one table that refers to the primary key of another table establishing a link between two tables.

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Primary Key (PK)

Unique identifier for each record in a table

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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 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

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