Lecture 4- Entity Relations Model Flashcards
Describe the database design process
What are the three things that describe ER model
- Entities
- Relationships
- Attributes
What is an entity?
A distinguishable object
What is an entity set?
A set of entities fo the same type
What is a relationship?
Represents the fact that certain entities are related to each other
What is a relationship set?
Set of relationships of the same type
What is an attribute?
Describes a property of an entity or a relationship
What is a key?
A minimal set of attributes that uniquely identifies each entity in an entity set
What is a role?
The function of an entity set in a relationship set
What type of relationship is this?
Binary, many to many
What type of relationship is this?
Binary, many to one
What type of relationship is this?
Binary, one to one
What type of relationship is this?
Ternary relationship
What type of relationship is this?
Participation constraint
What is this double circle?
Set value attributes
What relationship is this?
Weak entity
What is a weak entity?
A weak entity models an entity which is part of an owner entity, and it cannot be uniquely identified without the primary key of the owner entity
What type of relationship is a weak entity?
Many to one
____ cannot be uniquely identified by their own attributes alone and rely on the strong entitys primary key for their identification
Weak entities
What type of relationship is this?
ISA Hierarchy
What are some properties of ISA?
- Inheritance
- Transitivity = hierarchy of IsA
- Reasons for using IsA
Superclass vs subclass
- Superclass = generalization (it contains attributes that are common to all entities in the hierarchy)
- Subclass = specialization (it inherits all the attributes of the superclass and can have additional attributes of its own)
Review the types of relationships
Create this table
