entity relationship diagram or ERD is always required while starting any database project. myassignmenthelp provides help with all kinds of such assignments.

1. Entity Relationship
Diagrams
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2. Entity-Relationship Diagram
• Entity-Relationship (E-R) Diagram
– A detailed or logical representation of the
entities, associations as well as data
components to have an organization or
maybe small business.
• Notation works by using several key
constructs.
– Data entities
– Relationships
– Attributes
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3. Entity
• An entity can be a enterprise object which
signifies an organization, or even group of
data.
• A person, place, object, event or even idea within the
user environment about which the business wants in
order to maintain data
• Symbolized with a rectangle in E-R diagrams
• Notation:
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4. Attribute
• An attribute is a sub-group associated with
information within an entity.
• A named property or even attribute of an entity that is
associated to an organization
• Notation:
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5. ER Diagram Notations
• Week entity
Relationship
Multivalued
attribute
Key attribute
Strong Weak
Relationship
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6. Example:
carry
books indexwrote subjectauthor
s
SS#
name
title
librariesaddress
isbn
Subject
matter
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7. Binary Relationship
The binary relationship between entity set A as
well as B may be:
• 1:1 Women marrying Men (function)
• N:1 Children having mothers (function)
marry men
having mothers
1n
A B
A B
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8. Cont….
• 1:N Mothers having children (inverse
function)
• M:N Students enrolled in a class
having children
n1
A B
enrolled classes A B
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9. Key
• Identification associated with any kind of data
type.
• The various kinds of KEY attribute are:
– Super Key
– Candidate Key
– Primary Key
– Foreign Key
– Composite Key
– Alternate Key
– Secondary Key
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10. Super Key:
• An attribute as well as combining attribute that is used to
identify the records uniquely. A table can have a lot of
Super Keys.
– For example:
(ID), (ID,Name), (ID,Address), (ID,Department_ID),
(ID,Salary),
The like because any kind of mixture which could
determine the actual records uniquely would have been
a Super Key.
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11. Candidate Key:
• Is a column in a table that is able to be a primary key.
– For example:
1)ID
2)Name, address
We have only two Candidate Keys used to determine the
actual records from the table uniquely. “ID” Key may
determine the actual record uniquely and combined of
Name and Address can identify the record uniquely,
however nor "Name" neither "Address" may be used
to determine the actual "records uniquely“ as it might
be possible that we have two employees with similar name
or two employees from the same house.
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12. Primary Key:
• The attribute or as well as combined attributes
that uniquely define the record.
• For example:
Database custom may use among the Candidate Key
like Primary Key. In this instance we now have “ID” as
well as “Name, Address” as Candidate Key, Consider
“ID” Key as a Primary Key as the other key is the
combination of more than one attribute.
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13. Foreign Key:
• An attribute or combined attribute in a table whose value
match a primary key in another table.
 Composite Key:
A primary key which includes several attributes is called
 For example: if we have used “Name, Address” as a
Primary Key then it will be our Composite Key.
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14. Alternate Key:
 The candidate keys that is not the main primary key is
called an alternate key.
 For example: “Name, Address” as it is the only other
Candidate Key that is not a Primary Key.
 Secondary Key:
Alternative associated with primary key.
 For example: Name, Address, Salary, Department_ID
etc. as they can determine the records but they might
not be unique.
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