the ladakh protest in leh ladakh 2024 sonam wangchuk.pptx
EER MODEL
1. Extended Entity-Relationship
(EER) Model
Asst.Prof. Rupali Lohar
Dept. of Computer Science & Engineering
B. R. Harne College Of Engineering & Technology, Karav, Post Vangani (W Tal
Ambernath, Mumbai, Maharashtra 421503
2. Extended Entity-Relationship (EER) Model
• some improvements or enhancements were made to the existing ER
Model to make it able to handle the complex applications better.
• three new concepts were added to the existing ER Model, they were:
• Generalization
• Specialization
• Aggregation
3. Generalization
• Generalization is a bottom-up approach in which two lower level
entities combine to form a higher level entity.
• In generalization, the higher level entity can also combine with other
lower level entities to make further higher level entity.
4. • Representation of specialization/generalization in ER diagrams
• A diamond notation is a common representation of
specialization/generalization relationships in ER diagrams.
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6. • For example, Saving and Current account types entities can be
generalised and an entity with name Account can be created, which
covers both.
7. Specialization
• Specialization is opposite to Generalization. It is a top-down approach
in which one higher level entity can be broken down into two lower
level entity.
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9. Aggregation
• Aggregation represents a relationship between entity types, where
one represents the whole and the other the part.
• An example of aggregation is the Car and Engine entities. A car is
made up of an engine. The car is the whole and the engine is the part.
Aggregation does not represent strong ownership. This means, a part
can exist on its own without the whole.
10. • Aggregation is a process in which a single entity alone is not able to
make sense in a relationship so the relationship of two entities acts as
one entity.
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12. • An example of aggregation is the 'Teacher' entity following the
'syllabus' entity act as a single entity in the relationship. In simple
words, aggregation is a process where the relation between two
entities is treated as a single entity.
14. • Disjoint: The disjoint constraint only applies when a superclass has
more than one subclass. If the subclasses are disjoint, then an entity
occurrence can be a member of only one of the subclasses, e.g.
postgrads or undergrads you cannot be both. To represent a disjoint
superclass/subclass relationship,
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17. • Overlapping: This applies when an entity occurrence may be a
member of more than one subclass.
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19. • Total: Each superclass (higher-level entity) must belong to subclasses
(lower-level entity sets), e.g. a student must be postgrad or
undergrad. To represent completeness in the
specialization/generalization relationship, the keyword Mandatory is
used.
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21. • Partial: Some superclasses may not belong to subclasses (lower-level
entity sets), e.g. some people at UCT are neither student nor staff.
The keyword Optional is used to represent a partial
specialization/generalization relationship.
22. • We can show both disjoint and completeness constraints in the ER
diagram. Following our examples, we can combine disjoint and
completeness constraints.
23. • Some members of a university are both students and staff. Not all
members of the university are staff and students.
