Podcast
Questions and Answers
What is a characteristic of a strong entity?
What is a characteristic of a strong entity?
- Dependent on another entity
- Cannot exist on its own
- Does not have a unique identifier
- Has its own unique identifier (correct)
How is a weak entity different from a strong entity?
How is a weak entity different from a strong entity?
- Has a unique identifier
- Can exist on its own
- Exists independently of other entities
- Dependent on a strong entity (correct)
What does a double underline in an entity box signify?
What does a double underline in an entity box signify?
- Unique identifier
- Strong entity
- Partial identifier (correct)
- Weak entity
In the context of identifying relationships, what do they link together?
In the context of identifying relationships, what do they link together?
When should a relationship with attributes become an associative entity?
When should a relationship with attributes become an associative entity?
What is an entity in the context of a database?
What is an entity in the context of a database?
Which of the following is a characteristic of identifiers (keys) in a database?
Which of the following is a characteristic of identifiers (keys) in a database?
What does a composite attribute refer to in a database?
What does a composite attribute refer to in a database?
In the context of attributes, what does 'single-valued' imply?
In the context of attributes, what does 'single-valued' imply?
What is the purpose of an identifier (key) in a database?
What is the purpose of an identifier (key) in a database?
How are identifiers (keys) differentiated from other attributes in a database?
How are identifiers (keys) differentiated from other attributes in a database?
What describes features pertaining to the association between entities in a relationship?
What describes features pertaining to the association between entities in a relationship?
In the E-R model, what is the degree of a relationship?
In the E-R model, what is the degree of a relationship?
What type of relationship involves three different entity types related to each other?
What type of relationship involves three different entity types related to each other?
What does 'One-to-Many' cardinality mean in a relationship?
What does 'One-to-Many' cardinality mean in a relationship?
What defines the minimum number of instances one entity can be associated with another in an E-R diagram?
What defines the minimum number of instances one entity can be associated with another in an E-R diagram?
In an E-R model, what is an instance between specific entity instances?
In an E-R model, what is an instance between specific entity instances?
Which type of constraint specifies the maximum number of instances one entity can be associated with another in a relationship?
Which type of constraint specifies the maximum number of instances one entity can be associated with another in a relationship?
What does a Unary Relationship involve in the E-R model?
What does a Unary Relationship involve in the E-R model?
What is represented by Multiple Relationships in an E-R diagram?
What is represented by Multiple Relationships in an E-R diagram?
How is 'Many-to-Many' cardinality defined in a relationship?
How is 'Many-to-Many' cardinality defined in a relationship?
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Study Notes
Entity Characteristics
- A strong entity has a unique existence, independent of other entities.
- A weak entity, on the other hand, exists only in relation to another entity.
Entity Representation
- A double underline in an entity box signifies a weak entity.
Relationships
- Relationships link together entities.
- A relationship with attributes becomes an associative entity when it has its own attributes.
Entity Definition
- In the context of a database, an entity is an object or concept that has existence and can be described with a set of attributes.
Identifier (Key) Characteristics
- An identifier (key) is a unique characteristic that distinguishes one entity from another.
- Identifiers (keys) are differentiated from other attributes by being unique and non-null.
Attribute Characteristics
- A composite attribute is made up of multiple simpler attributes.
- A single-valued attribute implies that each entity instance has only one value for that attribute.
Identifier (Key) Purpose
- The purpose of an identifier (key) is to uniquely identify each instance of an entity.
Relationship Descriptions
- Features pertaining to the association between entities in a relationship are described by relationship attributes.
E-R Model Concepts
- The degree of a relationship refers to the number of entities involved in the relationship.
- A ternary relationship involves three different entity types related to each other.
- One-to-Many cardinality means that one instance of an entity can be associated with multiple instances of another entity.
- The participation constraint defines the minimum number of instances one entity can be associated with another in an E-R diagram.
- A unary relationship involves only one entity type.
- Multiple relationships are represented by multiple lines connecting entities in an E-R diagram.
- Many-to-Many cardinality means that multiple instances of one entity can be associated with multiple instances of another entity.
- The cardinality constraint specifies the maximum number of instances one entity can be associated with another in a relationship.
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