• 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
– Data entities
• An entity can be a enterprise object which
signifies an organization, or even group of
• 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
• 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
books indexwrote subjectauthor
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)
• 1:N Mothers having children (inverse
• M:N Students enrolled in a class
enrolled classes A B
• Identification associated with any kind of data
• The various kinds of KEY attribute are:
– Super Key
– Candidate Key
– Primary Key
– Foreign Key
– Composite Key
– Alternate Key
– Secondary Key
• An attribute as well as combining attribute that is used to
identify the records uniquely. A table can have a lot of
– For example:
(ID), (ID,Name), (ID,Address), (ID,Department_ID),
The like because any kind of mixture which could
determine the actual records uniquely would have been
a Super Key.
• Is a column in a table that is able to be a primary key.
– For example:
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.
• 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.
• An attribute or combined attribute in a table whose value
match a primary key in another table.
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.
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.
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.
For getting help with any
database related assignments