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Questions and Answers
What type of relationship occurs when an entity has a relationship to itself?
What type of relationship occurs when an entity has a relationship to itself?
Which cardinality describes a scenario where a single EMPLOYEE can be associated with many COMPUTER instances?
Which cardinality describes a scenario where a single EMPLOYEE can be associated with many COMPUTER instances?
What is a necessary step when dealing with many-to-many (N:M) relationships in data modeling?
What is a necessary step when dealing with many-to-many (N:M) relationships in data modeling?
What does maximum cardinality represent in an entity-relationship model?
What does maximum cardinality represent in an entity-relationship model?
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In a scenario where both an EMPLOYEE must have a BADGE and a BADGE is allocated to an EMPLOYEE, this relationship is categorized as:
In a scenario where both an EMPLOYEE must have a BADGE and a BADGE is allocated to an EMPLOYEE, this relationship is categorized as:
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What term describes a relationship that occurs between instances of the same entity type?
What term describes a relationship that occurs between instances of the same entity type?
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Which of the following is NOT a type of cardinality in an E-R model?
Which of the following is NOT a type of cardinality in an E-R model?
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When transforming a data model into a relational database, how are relationships of all degrees treated?
When transforming a data model into a relational database, how are relationships of all degrees treated?
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What type of relationship does the Computer_Assignment represent?
What type of relationship does the Computer_Assignment represent?
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Which statement correctly describes the Qualification relationship?
Which statement correctly describes the Qualification relationship?
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What is a primary key in the context of database entities?
What is a primary key in the context of database entities?
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Which of the following describes a surrogate key?
Which of the following describes a surrogate key?
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What happens when a row in the parent table is deleted and the ON DELETE action is set to CASCADE?
What happens when a row in the parent table is deleted and the ON DELETE action is set to CASCADE?
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What is the purpose of a foreign key in a database?
What is the purpose of a foreign key in a database?
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What is the function of the SET NULL action with foreign key constraints?
What is the function of the SET NULL action with foreign key constraints?
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What distinguishes an alternate key from a primary key?
What distinguishes an alternate key from a primary key?
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What distinguishes a weak entity from a strong entity?
What distinguishes a weak entity from a strong entity?
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What is an ID-dependent entity?
What is an ID-dependent entity?
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Which statement accurately describes the relationship between STUDENT and ADVISER?
Which statement accurately describes the relationship between STUDENT and ADVISER?
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Which of the following represents a non-ID-dependent weak entity?
Which of the following represents a non-ID-dependent weak entity?
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In data modeling, how is specialization used?
In data modeling, how is specialization used?
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What is the main requirement for a weak entity to exist?
What is the main requirement for a weak entity to exist?
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Which of the following is an example of an ID-dependent entity?
Which of the following is an example of an ID-dependent entity?
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How are non-ID-dependent weak entities represented in data modeling?
How are non-ID-dependent weak entities represented in data modeling?
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Study Notes
Recursive Relationships
- A recursive relationship is a relationship between different instances of the same entity.
- It is also known as a unary relationship.
- Recursive relationships can be one-to-one (1:1), one-to-many (1:N), or many-to-many (N:M).
Ternary Relationships
- Ternary relationships involve three entity classes.
- They are represented as combinations of binary relationships in relational database designs.
Cardinality
- Cardinality defines the number of entity instances that can participate in a relationship.
Maximum Cardinality
- One-to-one (1:1) relationship: At most one entity instance of each type is related.
- One-to-many (1:N) relationship: One entity instance can be associated with many instances of another type, but the reverse is not true.
- Many-to-many (N:M) relationship: Multiple instances of each entity type can be associated with each other.
Minimum Cardinality
- Minimum Cardinality specifies the minimum number of entity instances that must participate in a relationship instance.
Relationship Types Based on Minimum Cardinality
- Mandatory-to-mandatory (M-M) relationship: Entities are required on both sides of the relationship.
- Optional-to-optional (O-O) relationship: Neither entity is required to participate in the relationship.
- Optional-to-mandatory (O-M) relationship: An entity must be related to at least one instance of the other entity, but not vice versa.
Data Modeling Concepts: Identification
- Candidate key: A key that can serve as the primary key of an entity.
- Primary key: The candidate key selected to uniquely identify an entity instance.
- Alternate key: A candidate key that is not chosen as the primary key.
- Surrogate key: A DBMS-supplied identifier for each row of a table.
- Foreign key: A primary key of an entity used in another entity to identify related instances.
Action with Foreign Key Constraint
-
ON UPDATE
andON DELETE
actions specify how child table rows are affected when a parent table row is updated or deleted. - Actions include:
-
NO ACTION
: The operation on the parent table is rolled back. -
CASCADE
: The child rows are updated or deleted in the same way as the parent row. -
SET NULL
: Child rows are set to NULL. -
SET DEFAULT
: Child rows are set to their default values.
-
Strong Entities and Weak Entities
- A strong entity can exist independently.
- A weak entity depends on the presence of another entity for its existence.
- ID-dependent entities: Their identifier includes the identifier of another entity.
- Non-ID-dependent weak entities: They have their own identifier but still depend on another entity.
The Ambiguity of the Weak Entity
- A business rule may require a relationship, but logically, an entity can exist without it.
- Example: A STUDENT may need an ADVISER, but it can still exist without one.
Specialization and Generalization
- Specialization: Subgrouping entities of an entity type based on distinguishing characteristics.
- Generalization: Combining entities of different subtypes into a single entity type.
Crow's Foot Model
- A graphical representation of entity-relationship diagrams (ERDs) using symbols to represent relationships.
- It uses lines and symbols to depict the relationship's cardinality and participation constraints.
- The symbol is used to represent a relationship's type, such as 1:1, 1:N, or N:M.
- Participation constraints indicate whether an entity is required to participate in a relationship.
- Crow's foot notation provides a visual representation of data model relationships, helping to understand how entities connect and how data is structured.
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Description
Test your knowledge on recursive and ternary relationships in databases, along with concepts of cardinality. This quiz covers key definitions and examples to enhance understanding of how entities interact in relational database designs.