Each target entity is referenced car has manufacturer

(each target entity is referenced)
Car
has
Manufacturer
Car
[1..1] [0..n]
has
Manufacturer
Alternative for:
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ER Model: Unary Relationship
Self-referential on type-level
Different instances of the same type are related
Person
[0..1] [0..1]
married to
Husband
Wife
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ER Model: N-ary Relationship
Relationship type might involve more than 1 or 2 entity types
Example for ternary relationship type
Lecturer
teaches
Course
Room
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ER Model: N-ary Relationship /2
N-ary relationship type can not be replaced by n binary
relationship types
Semantics of following example different from previous: allows
lecturers to use rooms without a course taking place
Lecturer
teaches
Course
Room
takes place
uses
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ER Model: Weak Entity Types
Existential dependency to other entity Types
Identity (key attribute) includes key of master entity type
Relationship between weak entity type and its master type is
called identifying relationship
Building
N 1
has
Room
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Basic Extensions to the ER Model
Total or partial participation
Complex attributes
Derived attributes
Multi-valued attributes
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ER Extensions: Total Participation
Each entity of one type must relate to at least one of the other
entity type at least once
Graphical notation: thick or double line
Difference to functional relationship: entity may participate in
relationship several time
Student
of
University
Alternative for:
Student
[1..n] [0..n]
of
University
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ER Extensions: Partial Participation
Standard case: each entity of one type may or may not relate to
one or more entities of the other entity type
Graphical notation: thin line
Optional N:M-relationship
Person
owns
Car
Alternative for:
Person
[0..n] [0..n]
owns
Car
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ER Extensions: Complex Attributes
Composite attributes consisting of atomic attributes of different
types
Person
SSN
Name
Address
City
Street
ZIPcode
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ER Extensions: Multi-valued Attributes
Composite attributes consisting of variable set of values of the
same type
Person
SSN
Name
PhoneNumbers
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ER Extensions: Complex Attributes
Virtual attribute with value that can be computed from other
attributes or via relationships
Person
SSN
Name
Age
BirthDate
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Basic ER Extensions Summary
Only most common extensions were introduced here
Many others exist in books and DB design tools
Many different notations exist for the same concepts
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Object-oriented Extensions to the ER Model
Specialization as the derivation of sub-types
I
Semantic concept of the is_a -relationship
I
Various notations exist
I