0:06	in the last presentation we have seen
0:08	about the three tier architecture in
0:11	this presentation we will focus on the
0:13	view of data in the last presentation i
0:16	told you we have multiple views at the
0:18	presentation level why do we need
0:20	multiple views of data
0:23	the answer for this will be revealed in
0:25	this presentation before we step into
0:27	various views of data we need to
0:30	understand what is data abstraction i'll
0:33	explain data abstraction now we know
0:35	basically the primary goal of any
0:37	database is to store and retrieve the
0:39	data conveniently and effectively and
0:42	obviously we need storage for doing this
0:45	and this storage may involve simple or
0:47	even complex data structures we have
0:50	already seen about this in the second
0:52	presentation of this chapter
0:54	if you want more clarity i request you
0:56	to watch my previous lecture titled dbms
1:00	definition and now we will focus on the
1:02	data abstraction means hiding the
1:05	complexity why do we need to hide the
1:08	complexity in order to understand data
1:10	abstraction that is hiding the
1:12	complexity let's take an analogy for
1:14	better understanding let's assume we
1:17	have subscribed to a milk vendor and
1:20	every day we are getting milk packets
1:22	delivered to our home in time by the
1:24	milk vendor let's imagine there is some
1:26	delay in the delivery of milk package
1:28	for a particular day and we are
1:30	interested to know the reason for the
1:32	delay in the delivery of the milk packet
1:34	let's say we are enquiring the milk
1:36	delivery agent regarding the delay the
1:38	replay obviously from the milk delivery
1:40	agent will be the reason for the delay
1:42	and if he gives the reason that his
1:44	alarm was not working and that's why he
1:46	was not able to wake up on time that
1:49	would be sufficient for us
1:50	instead if the milk delivery agent
1:53	replies as that he has gone to the bed
1:55	last night at this time and he has woken
1:58	up twice and slept again alarm which he
2:00	has said has disappointed he still
2:02	continued sleeping it was six am already
2:05	for him but still he was sleeping it was
2:07	6 1 am and still he was sleeping and
2:09	blah blah blah who needs all this
2:12	information
2:13	we wanted only the reason for the delay
2:16	in other words we want a short and sweet
2:18	answer to be precise we want abstract
2:21	data not the complete data though we may
2:24	have encountered complexities but we
2:26	want only abstract information so we are
2:30
focusing on hiding the complexity and
2:33
providing only the essential details
2:36
that's what data abstraction is all
2:38
about in order to do that we have
2:41
several levels of abstraction we know
2:43
basically in a three-tier architecture
2:45
we have three levels likewise here we
2:47
have three levels the first level is the
2:50
physical level the second level is the
2:52
logical level and the third level is the
2:54
view level which is at the top most
2:56
level the user level in this
2:59
presentation we are going to see all the
3:01
levels one by one so we are sure that
3:03
there are three levels of data
3:05
abstraction
3:08
one is the physical level the other one
3:10
is the logical level and finally we have
3:12
the view level multiple views are there
3:16
let's see all the levels one by one in
3:18
detail
3:19
and the topic now is the various view of
3:22
data and we know basically there are
3:24
three levels the top level is the view
3:27
level followed by the middle level the
3:29
logical level followed by the bottommost
3:32
level the physical level
3:34
let's start with the first level the
3:35
physical level
3:37
what's this physical level is all about
3:39
this physical level is actually the
3:41
lowest level of abstraction now we know
3:44
this physical level is actually the
3:45
database level the physical storage is
3:47
involved we know databases are actually
3:49
stored in the physical medium right it
3:52
may be a hard disk or ssds any physical
3:55
medium and that's why it is the lowest
3:57
level of abstraction and it deals with
4:00
how the data are stored because the data
4:03
are actually stored in this level the
4:04
database actually exist in this level
4:07
and that's why this level deals with how
4:10
the data are stored when we talk about
4:12
how the data are stored it deals with
4:14
the data structures and this storage may
4:17
be involving simple data structures or
4:19
even complex data structures but please
4:21
be noted that these uses the low level
4:24
data structures in case we are storing
4:26
multimedia data in the database then
4:28
obviously the data structure would be
4:30
complex data structures
4:32
anyway we'll talk about the data
4:33
structures elaborately in the coming
4:35
presentations and we know this is
4:37
actually the database level we know data
4:40
are stored in the databases and these
4:42
databases are actually stored in the
4:44
storage medium and that's why this level
4:47
deals with storage
4:49
we are done with the bottom most level
4:51
the physical level let's now move on to
4:53
the next level
4:56
we know physical level deals with how
4:58
the data are stored
5:00
and this logical level deals with what
5:02
data are actually stored and what's the
5:04
relationship among the data stored so
5:07
logical level describes what data are
5:09
actually to be stored in the database
5:11
and what's the relationship among the
5:13
data that are stored in the database no
5:15
worries when we see relational database
5:17
er models we will understand about the
5:19
relationship among the data for now just
5:22
understand this level the logical level
5:24
deals with what data are actually stored
5:27
the physical level deals with how the
5:29
data are stored logical level deals with
5:31
what data are stored and the
5:33
relationship among the data and what
5:35
about the data
5:36
structures for example if you are
5:38
storing the entire database this entire
5:41
database may be involving simple data
5:43
structures or even complex data
5:45
structures but storing the data
5:47
physically at this level at the physical
5:49
level involves more complexity but at
5:51
the logical level it may use only simple
5:54
data structures just see at the logical
5:57
level we use only simple data structures
5:59
but at the physical level we use complex
6:01
data structures how these simple data
6:04
structures interact with complex data
6:06
structures
6:07
that's what this point there exists
6:09
physical data independence what do we
6:12
mean by this and we know this logical
6:14
level is at the application level right
6:16
this is at the application now the
6:19
applications actually do not depend on
6:21
the physical level or the physical
6:23
schema don't worry about the term schema
6:26
in the next lecture i will explain about
6:27
schema elaborately for now just
6:29
understand the structure of the database
6:31
is referred as schema so when we have
6:34
the existing structure at the physical
6:36
level and when we make some changes in
6:38
the logical level it doesn't mean that
6:41
we need to rewrite the entire structure
6:43
in the physical level simply
6:46
applications do not depend on the
6:48
physical schema so we need not rewrite
6:50
the physical structure if there is a
6:52
change in the logical structure because
6:55
these logical structures are going to
6:56
use only simple data structures and
6:59
there should exist physical data
7:01
independence so that if any changes are
7:04
made in the logical level it will not
7:06
affect the physical level and obviously
7:08
who is going to write all the logic
7:10
the database administrator what to store
7:13
how to store everything is done by the
7:15
database administrator of course he is
7:17
involved in all the levels but the
7:19
actual logic is involved in the logical
7:21
level
7:23
we are done with the logical level let's
7:25
now move on to the top most level the
7:27
view level and we know there are
7:29
multiple views existing and we know this
7:32
is the highest level of abstraction it
7:34
means it involves more complexity and we
7:37
are going to hide most of the complexity
7:39
at this level why
7:41
because we need not show the
7:43
complexities to the user say if a user
7:45
wants to transfer fund from one account
7:47
to another account he should be given
7:49
with the option how to do the transfer
7:52
at the back end at the logical level or
7:54
at the physical level multiple
7:56
complexities are involved we need not
7:58
show that complexity to the user and
8:01
that's why this level deals with the
8:03
users and the access to the users so
8:06
granting privileges everything will be
8:08
coming under this level and we know this
8:10
is the view level where user is going to
8:12
interact so obviously the interaction
8:14
with the system is done at this level
8:16
how the user is going to interact with
8:18
the system through the interfaces it may
8:20
be a web interface or a mobile interface
8:22
simply gui the graphical user interface
8:25
gui and also this level is going to
8:28
interact with the next level that is the
8:30
logical level where application programs
8:32
are written and as mentioned multiple
8:35
views exist in this level and of course
8:37
we need to focus on the security of
8:39
multiple views how multiple views exist
8:42
in this level we know all data are
8:44
stored in a central place let's take
8:46
banking environment a normal user will
8:48
be able to access his own data a teller
8:51
may access some more data than the
8:53
normal user but he will be able to give
8:55
assistance to the customers or users
8:57
with the basic details think about the
8:59	bank manager he'll be obviously having
9:02	more privileges when compared to other
9:04	users in its branch
9:06	and what about the regional manager he
9:08	or she will have more privilege when
9:10	compared to the branch manager it
9:12	doesn't mean that data are stored
9:13	separately for every user all data are
9:16	stored in the same database but there
9:18	exist multiple views i'll give you one
9:20	more example just assume you are going
9:23	to atm machine for withdrawing your
9:25	money when you insert your atm card only
9:27	your details are fetched this is view
9:30	one when i go and insert my atm card the
9:33	database system will provide only my
9:34	details this is another view see this is
9:37	how multiple views are existing and also
9:40	there is security that is strongly
9:41	enforced that i can access only my data
9:44	where i am not given with others data
9:46	that's how security is also achieved at
9:48	the view level this is just an example
9:51	anyway when the course progresses we
9:53	will be able to understand even more
9:55	things about multiple views and security
9:58	and that's it guys i hope in this
10:00	presentation we have seen various views
10:02	of data in the next presentation i will
10:04	teach you what is schema and instance i
10:07	hope the session is informative and
10:09	thank you for watching
10:11	[Music]
10:11	[Applause]
10:13	[Music]
10:21	you