Entity set & it's types
1.What is entity?
Ans/- An entity can be a real word object either animated or inanimate that can be easily identifiable.
Ans/- An entity can be a real word object either animated or inanimate that can be easily identifiable.
Entity set: -
An entity set is a group of similar kind of entities. It may contain entities
with attributes sharing similar values. Entities are represents by their
properties which also called attributes.
Type of
entity: -
Weak
entity: - A weak entity is a type of entity which doesn’t have its key attribute. It
can be identified uniquely by considering by consisting primary key of another
entity. It represented by double rectangular box. Weak relation represent by
double diamond box.
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Strong entity: - A
strong entity is a type of entity which has its key attribute for that strong
entity said need not to have participation.
Difference
between strong and weak entity: -
Strong
entity
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Weak entity
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1. Strong entity
set always has a primary key.
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1. It
doesn’t have enough attributes to build a primary key.
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2. It is
represented by a rectangular symbol.
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2. It is
represented by double rectangular symbol.
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3. Member of a
strong entity set is called as dominate entity set.
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3. Member of a
weak entity set is called as a subordinate entity set.
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4. In the ER
diagram the relationship between two strong entities set shown by a diamond
symbol.
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4. The
relationship between one strong and weak entity set shown by double diamond
symbol.
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