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View of Data | Neso Academy | YouTubeToText
YouTube Transcript: View of Data
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in the last presentation we have seen
about the three tier architecture in
this presentation we will focus on the
view of data in the last presentation i
told you we have multiple views at the
presentation level why do we need
multiple views of data
the answer for this will be revealed in
this presentation before we step into
various views of data we need to
understand what is data abstraction i'll
explain data abstraction now we know
basically the primary goal of any
database is to store and retrieve the
data conveniently and effectively and
obviously we need storage for doing this
and this storage may involve simple or
even complex data structures we have
already seen about this in the second
presentation of this chapter
if you want more clarity i request you
to watch my previous lecture titled dbms
definition and now we will focus on the
data abstraction means hiding the
complexity why do we need to hide the
complexity in order to understand data
abstraction that is hiding the
complexity let's take an analogy for
better understanding let's assume we
have subscribed to a milk vendor and
every day we are getting milk packets
delivered to our home in time by the
milk vendor let's imagine there is some
delay in the delivery of milk package
for a particular day and we are
interested to know the reason for the
delay in the delivery of the milk packet
let's say we are enquiring the milk
delivery agent regarding the delay the
replay obviously from the milk delivery
agent will be the reason for the delay
and if he gives the reason that his
alarm was not working and that's why he
was not able to wake up on time that
would be sufficient for us
instead if the milk delivery agent
replies as that he has gone to the bed
last night at this time and he has woken
up twice and slept again alarm which he
has said has disappointed he still
continued sleeping it was six am already
for him but still he was sleeping it was
6 1 am and still he was sleeping and
blah blah blah who needs all this information
information
we wanted only the reason for the delay
in other words we want a short and sweet
answer to be precise we want abstract
data not the complete data though we may
have encountered complexities but we
want only abstract information so we are
focusing on hiding the complexity and
providing only the essential details
that's what data abstraction is all
about in order to do that we have
several levels of abstraction we know
basically in a three-tier architecture
we have three levels likewise here we
have three levels the first level is the
physical level the second level is the
logical level and the third level is the
view level which is at the top most
level the user level in this
presentation we are going to see all the
levels one by one so we are sure that
there are three levels of data abstraction
abstraction
one is the physical level the other one
is the logical level and finally we have
the view level multiple views are there
let's see all the levels one by one in detail
detail
and the topic now is the various view of
data and we know basically there are
three levels the top level is the view
level followed by the middle level the
logical level followed by the bottommost
level the physical level
let's start with the first level the
physical level
what's this physical level is all about
this physical level is actually the
lowest level of abstraction now we know
this physical level is actually the
database level the physical storage is
involved we know databases are actually
stored in the physical medium right it
may be a hard disk or ssds any physical
medium and that's why it is the lowest
level of abstraction and it deals with
how the data are stored because the data
are actually stored in this level the
database actually exist in this level
and that's why this level deals with how
the data are stored when we talk about
how the data are stored it deals with
the data structures and this storage may
be involving simple data structures or
even complex data structures but please
be noted that these uses the low level
data structures in case we are storing
multimedia data in the database then
obviously the data structure would be
complex data structures
anyway we'll talk about the data
structures elaborately in the coming
presentations and we know this is
actually the database level we know data
are stored in the databases and these
databases are actually stored in the
storage medium and that's why this level
deals with storage
we are done with the bottom most level
the physical level let's now move on to
the next level
we know physical level deals with how
the data are stored
and this logical level deals with what
data are actually stored and what's the
relationship among the data stored so
logical level describes what data are
actually to be stored in the database
and what's the relationship among the
data that are stored in the database no
worries when we see relational database
er models we will understand about the
relationship among the data for now just
understand this level the logical level
deals with what data are actually stored
the physical level deals with how the
data are stored logical level deals with
what data are stored and the
relationship among the data and what
about the data
structures for example if you are
storing the entire database this entire
database may be involving simple data
structures or even complex data
structures but storing the data
physically at this level at the physical
level involves more complexity but at
the logical level it may use only simple
data structures just see at the logical
level we use only simple data structures
but at the physical level we use complex
data structures how these simple data
structures interact with complex data structures
structures
that's what this point there exists
physical data independence what do we
mean by this and we know this logical
level is at the application level right
this is at the application now the
applications actually do not depend on
the physical level or the physical
schema don't worry about the term schema
in the next lecture i will explain about
schema elaborately for now just
understand the structure of the database
is referred as schema so when we have
the existing structure at the physical
level and when we make some changes in
the logical level it doesn't mean that
we need to rewrite the entire structure
in the physical level simply
applications do not depend on the
physical schema so we need not rewrite
the physical structure if there is a
change in the logical structure because
these logical structures are going to
use only simple data structures and
there should exist physical data
independence so that if any changes are
made in the logical level it will not
affect the physical level and obviously
who is going to write all the logic
the database administrator what to store
how to store everything is done by the
database administrator of course he is
involved in all the levels but the
actual logic is involved in the logical level
level
we are done with the logical level let's
now move on to the top most level the
view level and we know there are
multiple views existing and we know this
is the highest level of abstraction it
means it involves more complexity and we
are going to hide most of the complexity
at this level why
because we need not show the
complexities to the user say if a user
wants to transfer fund from one account
to another account he should be given
with the option how to do the transfer
at the back end at the logical level or
at the physical level multiple
complexities are involved we need not
show that complexity to the user and
that's why this level deals with the
users and the access to the users so
granting privileges everything will be
coming under this level and we know this
is the view level where user is going to
interact so obviously the interaction
with the system is done at this level
how the user is going to interact with
the system through the interfaces it may
be a web interface or a mobile interface
simply gui the graphical user interface
gui and also this level is going to
interact with the next level that is the
logical level where application programs
are written and as mentioned multiple
views exist in this level and of course
we need to focus on the security of
multiple views how multiple views exist
in this level we know all data are
stored in a central place let's take
banking environment a normal user will
be able to access his own data a teller
may access some more data than the
normal user but he will be able to give
assistance to the customers or users
with the basic details think about the
bank manager he'll be obviously having
more privileges when compared to other
users in its branch
and what about the regional manager he
or she will have more privilege when
compared to the branch manager it
doesn't mean that data are stored
separately for every user all data are
stored in the same database but there
exist multiple views i'll give you one
more example just assume you are going
to atm machine for withdrawing your
money when you insert your atm card only
your details are fetched this is view
one when i go and insert my atm card the
database system will provide only my
details this is another view see this is
how multiple views are existing and also
there is security that is strongly
enforced that i can access only my data
where i am not given with others data
that's how security is also achieved at
the view level this is just an example
anyway when the course progresses we
will be able to understand even more
things about multiple views and security
and that's it guys i hope in this
presentation we have seen various views
of data in the next presentation i will
teach you what is schema and instance i
hope the session is informative and
thank you for watching [Music]
[Music] [Applause]
[Applause] [Music]
[Music] you
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