ERD Flashcards
A thing in the real world with an independent existence (house, person
Entity
May be an object with physical existence or with a consensual existence (course, job)
Entity
Properties that describe the entities
Attributes
TYPES OF ATTRIBUTES
Composite attributes
Simple attributes
Single valued attributes
Multivalued attributes
Derived attributes
Stored attributes
Can be divided into further parts
Composite attributes
Cannot be divided further
Simple attributes
Have a single value for a particular entity
Single valued attributes
Can have set of values for a particular entity
Multivalued attributes
Can be derived from other attributes
Derived attributes
From which the value of other attributes are derived
Stored attributes
Has multivalued and composite components in it
Complex attributes
Multivalued attributes represented within
{ }
Composite values represented within
( )
Something not applicable or unknown
Null values
Collection of entities that have the same attributes
Entity types
Collection of entities of a particular entity type at a point in time
Entity set
Attribute that is capable of identifying each entity uniquely
Key attribute
The set of values that can be assigned to an attribute
Value set of attributes
database design process
- requirements collection and analysis
- conceptual design
- logical design (data model mapping)
- physical design
Database designers understand and document the data requirements of the database users
Requirements collection and analysis
Consists of user-defined operations
Functional requirements
Creating conceptual schema
Conceptual design
Concise description of the data requirements and detailed descriptions of the entity types relationships and constraints
conceptual schema
Actual implementation of the database, using commercial DBMS
Logical design (data model mapping)
The internal storage structures, indexes, access paths are specified
Physical design
Do not key attributes of their own
WEAK ENTITY TYPES
Identified by relating to another entity type called the identifying or the owner entity type
WEAK ENTITY TYPES
Relationship between weak entity type to its owner
Identifying relationship
different symbols used in erd
entity
weak entity
attributes
key attribute
multivalued attribute
composite attribute
derived attribute
identifying relationship
Association among 2 or more entities
Relationship
Denotes the number of entity types that participate in a relationship
Degree of relationship
degrees of relationship
unary relationship
binary relationship
ternary relationship
relationship constraints
cardinality ration
participation constraints
maximum number of relationship instances that can entity can participate in (1:1, 1:N, N:1, M:N)
Cardinality ratio
specifies whether existence of an entity depends on its being related to another entity
Participation constraints
2 types of participation
total participation
partial participation
attributes of relationship types
1:1
- 1:1
1:N
M:N
Signifies the role that a participating entirety plays in each relationship instance
Role names
Same entity type participates more than once in a relationship type in different roles
Recursive relationships
enhanced er model
generalization
specialization
Bottom up approach where two lower level entities combine to form a higher level entity
Generalization
Top down approach where it defines set of subclasses on an entity type
Specialization
