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