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Enhanced entity-relationship modelling concepts. (Lecture 3)
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Enhanced Entity-RelationshipModelling Concepts
Lecture 3
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Agenda•1.Relationships with degree higher
then 2
• 2.EER concepts specialisation/generalisation
• 3.Alternative ER/EER notation
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1.Relationships with degree higher then 2Type
Strong
Entity
Occurrence
Type
Relationship
Occurrence
Degree
Multiplicity
Cardinality
Single valued
Attribute
Multi valued
Weak
Participation
Complex
Simple
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1.Relationships with degree higher then 2• Degree of a Relationship
• Number of participating entities in relationship.
• Relationship of degree:
• two is binary;
• three is ternary;
• four is quaternary.
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1.Relationships with degree higher then 2• Ternary relationship called ‘Registers’
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1.Relationships with degree higher then 2• Quaternary relationship called ‘Arranges’
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1.Relationships with degree higher then 2• Multiplicity for Complex Relationships
• Number (or range) of possible occurrences of an entity
type in an n-ary relationship when other (n-1) values are
fixed.
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1.Relationships with degree higher then 2• Ternary relationship called ‘Registers’
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1.Relationships with degree higher then 2• Ternary relationship called ‘Registers’ with Values for Staff
and Branch Entities Fixed
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1.Relationships with degree higherthen 2
• Try to detect multiplicities for remaining participating entities
in ternary relationship Registers
• Note: You can make appropriate assumptions and
detect multiplicities accordingly
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Agenda• 1.Relationships with degree higher then 2
•2.EER concepts
specialisation/generalisation
• 3.Alternative ER/EER notation
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2.1.The Enhanced Entity-Relationship Model• Semantic concepts are incorporated into the original ER
model and called the Enhanced Entity-Relationship (EER)
model.
• Examples of additional concepts of EER model are:
• specialization / generalization;
• aggregation;
• composition.
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2.2. Specialisation/Generalisation• Superclass
An entity type that includes one or more distinct subgroupings of
its occurrences.
• Subclass
A distinct subgrouping of occurrences of an entity type.
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2.2. Specialisation/Generalisation• Superclass/subclass relationship is one-to-one (1:1).
• Superclass may contain overlapping or distinct subclasses.
• Not all members of a superclass need to be a member of a
subclass.
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2.2. Specialisation/Generalisation• Attribute Inheritance
• An entity in a subclass represents same ‘real world’
object as in superclass, and may possess subclassspecific attributes, as well as those associated with the
superclass.
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2.2. Specialisation/Generalisation• Specialization
• Process of maximizing differences between members of
an entity by identifying their distinguishing
characteristics.
• Generalization
• Process of minimizing differences between entities by
identifying their common characteristics.
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2.2. Specialisation/Generalisation19.
2.2. Specialisation/Generalisation20.
2.2. Specialisation/Generalisation21.
2.2. Specialisation/Generalisation22.
2.3. Multiplicity constraints inSpecialisation/Generalisation
• Participation constraint
• Determines whether every member in superclass must
participate as a member of a subclass.
• May be mandatory (total) or optional.
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2.3. Multiplicity constraints inSpecialisation/Generalisation
• Disjoint constraint
• Describes relationship between members of the
subclasses and indicates whether member of a
superclass can be a member of one, or more than one,
subclass.
• May be disjoint (OR) or overlapping (AND)
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2.3. Multiplicity constraints inSpecialisation/Generalisation
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2.3. Multiplicity constraints inSpecialisation/Generalisation
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2.3. Multiplicity constraints inSpecialisation/Generalisation
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2.4. EER28.
2.5. Aggregation• Represents a ‘has-a’ or ‘is-part-of’ relationship between entity types, where one
represents the ‘whole’ and the other ‘the part’.
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2.6. Composition• Specific form of aggregation that represents an association between entities,
where there is a strong ownership and coincidental lifetime between the ‘whole’
and the ‘part’.
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Agenda• 1.Relationships with degree higher then 2
• 2.EER concepts specialisation/generalisation
•3.Alternative ER/EER notation
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3.1. Chen’s ER-diagram notationSymbol
Meaning
ENTITY TYPE
WEAK ENTITY TYPE
RELATIONSHIP TYPE
IDENTIFYING RELATIONSHIP TYPE
ATTRIBUTE
KEY ATTRIBUTE
MULTIVALUED ATTRIBUTE
COMPOSITE ATTRIBUTE
DERIVED ATTRIBUTE
TOTAL PARTICIPATION OF E2 IN R
E1
E1
E2
R
R
R
N
(min,max)
E2
E
CARDINALITY RATIO 1:N FOR E1:E2 IN R
STRUCTURAL CONSTRAINT (min, max) ON
PARTICIPATION OF E IN R
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3.1. Chen’s ER-diagram notation33.
3.1. Chen’s ER-diagram notation34.
3.1. Chen’s ER-diagram notation35.
3.1. Chen’s ER-diagram notation36.
3.1. Chen’s ER-diagram notation37.
3.1. Chen’s ER-diagram notation38.
ReadingConnolly & Begg, Chapter 13