Chapter 3 Flashcards
Entity
A thing in a real world with independent existence.
Ex: house ,person,job…
Attributes
Properties that describe the entities.
Ex: name,age,phone…
Composite attributes
Can be divide into further parts. Ex name-> last name,first name, middle name
Simple attributes
Cannot be divided into further parts. Ex:weight
Single valued attributes
Have a single value for a particular entity
Multivalued attributes
Can have set of values for a particular entity.
Ex: degree
Derived attributes
Can be derived from other attributes.
Ex: age can be derived from DOB
Stored attributes
From which the values of other attributes are derived
Ex: DOB
Complex attributes
Multivalued and composite
Multivalued {}
Composite()
Ex: {college degree(year,degree,field)}
Null values
Not applicable or unknown
Entity type
A collection of entities that have the same attributes
Entity set
Collection of entities of a particular entity type at a point in time.
key attribute
That attributes that is capable of identifying each entity uniquely
Relationship
Association among 2 or more entites
Degree of relationship
Denotes the number of entity types that participates in a relationship
Unary relationship
Relation with one entity maa hala
Binary relationship
Relation with 2
Ternary relationship
Relation with 3 entities
Cardinality ratio
Maximum number of relationship instance that an entity can participate in.
Participation constraints
Total participation
Partial participation
Enhanced er model
Generalization : bottom-up approach lower level entities combine to form a higher level entity
Specialization: top-down higher level creat lower level entities
