Entities, Attributes and Relationships Video Lecture | SSC CGL Tier 2 - Study Material, Online Tests, Previous Year

hi my name is Shana he's Lauren and I am
doing the screencast assignment number
one the topics I will be covering today
are entities attributes and relationship
types so for entities an entity is a
noun that describes a person place
object event or concept usually is
correspondent to the RO examples of
entity are customers car houses lakes
books movies and theaters as you can see
here from these three tables there are
employees as your entity customers as
your entity and orders as your entity
now we have an entity type an entity
type is a collection of entities it's
used to be represented by a table an
entity instance is a single occurrence
of an entity type in our next example we
have a table representation and our
entity type which is employees and our
entity instances as highlighted here
each one of these our entity instances
types of entities there are two types of
it types of entities strong and weak a
strong entity is an independent entity
and its unique weak is a dependent
entity on a strong entity the
relationship is usually identified by a
double line as you can see here we have
a double box to represent our weak
entity and a single box to represent our
strong entity our relationship is
another by a double line that's how you
know that the weak entity is dependent
on this strong entity so a final exam is
dependent on this section of the class
now we have attributes attributes our
properties or characteristics of an end
it's usually denoted by a field so in
this table representation like our
lesson we have our entity which are
employees again and our attribute each
one of these are employee number our
first name last name and date of birth
is our attribute our entity instances
which is 101 david crystal and they're
all separate entity instances now there
are two types of attributes I'm going to
go over so we have required versus
optional required means you must have a
value in that field and optional is that
you have to have you can have you can
you can have it but that doesn't mean
you have to have it so an example here
is we'll have let's do this attribute
right now
date of birth this must be attribute so
we have to have a date of birth and turn
into these field however are optional
which is our employee office number
not every employee has an office number
and so this is optional David Bristol
has an office number 50 P whereas Mary
Manning does not maybe she's an intern
we don't know and that's why it's
unknown now we have simple and composite
so simple attribute if you go back here
simple attribute is just your regular
first-name and one field however your
composite attribute has meaningful
component parts such as your employee
address here you have your employee
address and it requires four parts to it
your street number your street name your
state and your zip code all these are a
composite attribute multivalued a multi
value attribute we take more than one
value for a given entity instance an
example would be that employee can have
more than one skill
derived attribute is that the value is
calculated from a related attribute
value so an example of that would be an
employee age is calculated through the
birth date and if we go to our table we
can calculate the age from our attribute
here and when we do that that is called
a derived attribute now let's go into
relationships we have our relationship
type which is modeled on top of a line
in between two entity types an example
of a relationship type the complete
parts of the relationship right here the
relationship instance is modeled as a
line in between the two entity types so
this is an instance so this is the type
and this is the instance the employee
can have a task but a task has to be
completed by an employee now you have
your cardinalities there cardinalities
of a relationship represents what your
minimum and maximum are so you can have
a one-to-one relationship or a
one-to-many relationship or a
many-to-many relationship here are an
example of your cardinality constraints
so you have your mandatory one-to-one
relationship a minimum of 1 and a
maximum of 1 let me go back we can see
that we have a one-to-one relationship a
task must be completed by a minimum of
one employee and a maximum of one
employee and then you have your minimum
of one and maximum of many or infinity
so this is a mandatory card in
cardinality your optional cardinalities
are denoted with a circle that means
your minimum does or does not have to
exist so your minimum is zero but your
maximum is one and here is your minimum
zero and your maximum is many so let's
look at the degrees of a relationship so
we have your unary whoops you have your
unary your binary and your ternary
relationships now there are two types of
unary relationships you're a one-to-one
so a person is married to a another
person this is a one-to-one relationship
which means one person told one then you
have your many to one or one many to
many relationship so your employee
manages one minimum or many employees
however many employees can only be
managed by a minimum of one employee or
a maximum of one employee now let's go
into binary binary has two entities your
two entities have a relationship now
your relationship is shown here your
theater has a max shows a maximum and a
minimum of one movie but your movie can
only be shown can be shown by a minimum
of one theater or many theaters this is
a binary relationship then you have your
ternary relationships which is three
attributes three attributes two denoted
by a relationship now a consultant signs
a contract with a relationship that is a
relationship among three attributes
let's go into associative entities types
so you have your binary relationship as
we saw before I'm not going to talk
about any of our minimum and maximum
cardinalities because we already went
over it but we have our employee and our
task this is a binary relationship
because this is a dotted line showing
that
you have an associate entity here your
employee can complete a task but you
want to have your date completed and you
know this is an associate identity by
the dotted line now an associative
entity from here we have a and B and
your table which your associative entity
should have a curved circle well not cur
circle but like a type not not straight
skirt curved edges so your a has a
cardinality of a minimum one maximum of
many and you have a table usually an
associate identity is to split up a
many-to-many relationship and that's why
the many-to-many relationship is facing
the associative entity and knob all the
way around and that is my screencast
assignment number one