Lesson 3 - Extended ER Model Flashcards
a detailed, logical representation of the data for an organization or for a business area.
E-R Model
Name this E-R Diagram Notation: Oval
Simple Attribute
Name this E-R Diagram Notation: Oval with Underline
Key Attribute
Name this E-R Diagram Notation: Oval with sub Attributes
Composite Attributes
Name this E-R Diagram Notation: Dashed Oval
Composite Attributes
Name this E-R Diagram Notation: Rectangle
Strong Entity
Name this E-R Diagram Notation: Double Rectangle
Weak Entity
Name this E-R Diagram Notation: Double Oval
Multivalued Attributes
Name this E-R Diagram Notation: Diamond
Relationship
includes all the modeling
concepts of the E-R Model and the concepts
of specialization, generalization, attributes
inheritance and aggregation
Extended ER Model
The process of designating subgrouping within an entity set is called
_____________.
For example, an entity set person, with attribute name, street and city. A
person may be further classified as one of the following:
* Customer
* Employee
DEPICTED BY A
TRIANGLE COMPONENT LABELED
“ISA”
Specialization
a simple inversion of specialization.
Generalization
Characteristics of Specialization:
- Stems from a single entity set
- Emphasizes difference among
entities within the set by creating
distinct lower-level entities sets. - The reason to apply
specialization is to represent
such distinct features.
Characteristics of Generalization:
- proceeds from the
recognition that a number of entity
sets share the same common
feature. - is used to emphasize
the similarities among lower-level
entity sets and to hide the
differences.
A crucial property of the higher and lower-level entities created by specialization and generalization is
The attribute of the higher-level entity sets are to be inherited by the lower-
level entity sets.
Attribute Inheritance
an abstraction through which relationships are treated as
higher lever entities.
Aggregation
An ER Diagram is not capable of representing relationships between entity
and a relationship which may be required in some scenarios.
Aggregation
Database can be represented with the help of _______ and these
notations can be reduced to collection of tables.
ER Notations
In converting E-R diagrams into tables we divide the E-R diagram into three
sections
- Strong entity set
- Weak entity set
- Relation set
The name of the table is the name of corresponding _________ of relationship name. Each table would have columns, the columns would be equal to the
number of _______ each entity have.
entities, attributes
