What is an Entity Relationship(ER) Model Video Lecture | Study Accountancy Class 11 - Commerce | Best Video for Commerce

here model has been used for past many
years in order to represent his design
this database maybe if you are
comfortable with or if you have gone
through these you know uml model set
based ones you can easily relate this in
your mental diagrams you have something
called as class right so exactly like
that we have with now I know your
diagrams it is like this in software
design know the way UML diagrams are
going to play the role in database
design your diagrams are going to play
the role of it and various things in our
you know your diagrams are one is called
as entity so here itself means entity
relationship model right ER model means
entity relationship model product and in
this entity relationship model they are
actually you know three things that you
should know one is called as entity okay
and the other is called as the
attributes and the other is called as
relationships okay so why do we
generally use this ER diagram just to
write in terms of pictures what is the
information we collected just like this
software design first we are going to
collect the requirements which means we
go and talk to the people like what do
they want and now they are going to say
in words you know they are going to
describe what they need then we are
going to convert their that I know word
description of their needs into this
diagrams right and now in the in
whenever they speak of something
whenever they say their needs there are
going to be nouns and the nouns are
nothing but the things are the object
for example they say person or car or or
in a board whatever so every object is
nothing but an entity so now when they
talk about it when they speak about it
when you collect the requirements the
norms are going to be the entities
alright and then works walls are going
to be relationship let us say a person
who owns a car right owns work
that is going to be relationship right
or if a employee works for a department
works for that is going to be
relationship right so now an entity is
nothing but any object in your database
is going to be an entity right and a
relationship is nothing but any verb
which you are going to describe is going
to be a relationship and what about
attributes attributes are again nouns
which describe these nouns for example a
person if he is an entity then he is
going to have attribute like this he is
going to have a name he is going to have
some A's and you know he's going to have
an address right phone number so all
these are going to be the attributes
right so now entity is nothing but you
can think of it like a thing right a
thing in our real world which is going
to be recorded in our database right and
that is what is called as entity and
what is an attribute is attribute or
nothing but the properties of the
entities or in order to better describe
the entity we are going to use
attributes right so you can think of it
as properties properties which are used
to better describe these things all
right for example you can think of a
entity as a person right and then how do
you describe a person may be using name
right and is and address phone number
all this okay and what is relationship
is you can think of relationship as
association among entities how are these
things related that is called as a
relationship how is a car related to a
person a person owns the car right or
how is the department related to a
employee if the employee works for the
department right and this is called as
relationship relationship is nothing but
what is the association among these
entities right so it is going to talk
about Association right for example what
is the association between employee and
a department works for so works fur is a
relationship all right so we have all
these three things which have to be
discussed in detail in in case of we are
diagrams okay so coming to this er
diagrams the terminologies like this you
know we are going to use set theory here
in the sense we talked about in tt type
and entity attribute it is okay and
relationship type and relationship okay
now what is entity entity and entity
type is we are going to talk about these
two things generally entity type right
and entity okay so what is entity type
is the name or the heading or the schema
schema is nothing but the heading for
example if I say person person is entity
type who is having attribute is name and
let us say address okay
now this entire thing is called as
entity type entity type will describe
the heading right it is also sometimes
called as schema so schema is nothing
but the description the heading right
and what about the entity entity is
nothing but a person who is going to be
represented in this entity type itself
for example let us say name is is you
know 26 and name is some Raju
right and let us say address is some
address is given now this is called as
entity so entity is actually an instance
and entity type is the heading right now
sometimes it is also called as intention
and it is called as extension so if you
want to think of it as a set theory
right this entire set the name of this
set is called as entity type and the
elements in this set they are called as
entities right and we are not going to
change entity types but then we might
add and delete some elements into the
entity type right therefore entities
they make
added or they might get you know deleted
and at any time the number of elements
are all the elements in any entity type
is called as state state of the entity
state of the generality is also called
as if I put all all of them together
state of the database what it so even
though this is quite you know it is used
but then generally people will call an
entity type as an entity and entity as
an indica type so they are going to use
them as if there is no difference
actually there is difference for you
entity type means just the name and
identity means the instance right so in
some questions you might have to observe
the difference and in general whenever
you know we speak in during the
explanation and sometimes use entity and
on sometimes use entity type then you
don't get confused from the context it
will be clear what it and the same
things will apply even for relationship
also all right relationship type and the
relationship itself so relationship
means it is actually an instance and
relationship type means what is it's
heading schema right so schema is
nothing but the heading the you know how
do you represent it okay and now in your
diagrams we don't use really entities we
use entity types which means we don't
really show you everything that is
present in the database we don't we
don't write a set diagram and then we
don't put a point for every element
present in it we are going to represent
it in a shortcut just using the entity
types therefore if you look at any air
diagram you are going to only see the
schemas the headings right not how many
elements are present in this and not any
set diagrams we are going to make it you
know keep it as simple as possible the
main intention of this diagram is to
help the communication between the
technical designer of the database and
the neighb user who does not know
anything about database he is just going
to say in words and you are supposed to
capture those nouns works and you are
supposed to put them in the diagram and
a refinement has to go on and for the
refinement to go on you have to sort
your suppose to show this diagram to
again the users
and they are going to say see this part
has to be improved or you know this
entity is going to have even more
attributes or they might even say some
constraints that you are again supposed
to capture and then and again refine it
for it so this is actually a cycle this
cycle goes on for some time okay so then
what happens is once we are done with
this diagram representation then we are
going to the next level so if you
remember it we are talking about the
conceptual design right so one once we
are done with the conceptual design then
we have to go with the representation
right then we have to go with the you
know physical representation so now we
are here talking conceptual design next
we will go for the representational
design so now we are going to use here
diagrams later we are going to use
relation tables which means later we are
going to take this air diagrams and
convert them to the relation tables and
later we are going to take the relation
tables and we are obviously going to
store them on the hard disk right
implementation so now we are going to
look at this let us see in depth about
each one of this right once you
understand them well then the conversion
of these into our diagrams into
relationship tables is going to be
straightforward okay