0:00	foreign
0:07	welcome back we are now in the next
0:10	chapter where we are going to focus on
0:12	relational databases in this
0:15	presentation we are going to focus on
0:17	the introduction to relational databases
0:19	in chapter 1 of this lecture series we
0:23	have seen a lot of data models what is a
0:26	data model it is the underlying
0:28	structure of a database and actually
0:30	this data model is a conceptual tool for
0:33	describing the data the relationship
0:35	among the data the data semantics and
0:38	the data constraints if you are directly
0:41	watching this lecture I request you to
0:43	navigate to the first chapter of this
0:45	playlist and please do watch the lecture
0:47	title data models and we have seen the
0:50	various categories of data models the
0:52	relational model The Entity relationship
0:55	model the object-based data model and
0:57	the semi-structured data model in this
1:00	chapter we are going to exclusively
1:01	focus on the relational databases where
1:04	relational databases follow those
1:06	relational model if you are clear with
1:08	relational model then understanding
1:10	relational databases is easy so why
1:13	waiting let's see the basic structure of
1:16	relational databases
1:18	what is a database basically a database
1:21	is a collection of tables and we know
1:24	what is a table a table is actually a
1:26	data structure that is used to describe
1:28	the data in rows and columns are tables
1:31	going to store only data no tables
1:35	represent both data and the relationship
1:37	I will explain you suppose if you have a
1:40	table with four attributes obviously we
1:42	store all the data in the tables and
1:45	this table is actually described by rows
1:47	and columns let's take I am talking
1:49	about a student table and this student
1:51	table contains multiple attributes or
1:54	columns let's take only two columns roll
1:56	number and name say for example if roll
1:59	number is 101 or 101 and the name of the
2:03	person is Muhammad Khan so if You
2:05	observe here the relationship is the
2:07	roll number one out one is pertaining to
2:09	the student Muhammad Khan or in other
2:12	words Muhammad Khan is having the roll
2:14	number 101 or 101 so what does it mean
2:18	this means there exists a relationship
2:21	among the values that are stored in the
2:23	table in other words when you have a row
2:25	each value in a row is having
2:28	relationship among other values and not
2:31	only this tables can also be used to
2:33
maintain the relationship among other
2:36
tables say for example an advisor table
2:39
can be used to maintain the relationship
2:41
between a student table and an
2:43
instructor table no worries I will
2:46
explain that shortly and that's why I
2:48
have mentioned here as tables represent
2:51
both the data and the relationship among
2:54
the data present in the table now in
2:56
relational model are we going to refer
2:58
this as table no we are going to refer
3:01
this as relation then why the term we
3:04
are using for representing tables as
3:06
relation in relational model because
3:09
there is a close association between the
3:11
dbms concept the table and the
3:14
mathematical concept the relation and
3:16
that's why in relational model we use
3:19
the term relation instead of referring
3:21
it as tables any way we will talk about
3:23
this elaborately in the coming lectures
3:25
for now just understand a table in
3:28
relational model or a table in
3:30
relational databases are referred as
3:32
relation basically relations are tables
3:35
but the important thing to note here is
3:37
it has a very close association with the
3:40
mathematical concept called relations
3:43
anyway you will understand about this
3:45
when we see the concepts relational
3:47
algebra and relational calculus in the
3:49
coming lectures for now just understand
3:51
a relation in relational database
3:54
management system is basically a table
3:56
only but we can apply many mathematical
3:59
operations on relations when you compare
4:02
with the table then what about the rows
4:04
and columns a row in a relation is
4:07
referred as Tuple and a column in a
4:09
relation is referred as attribute in a
4:12
table we represent rows and columns in
4:14
relation we represent it as Tuple and
4:17
attributes remember a tuple is basically
4:20
a row in a relation and coming to
4:23
attribute this is actually the column in
4:26
a relational database management system
4:27
and we have already talked about
4:29
instances and schemas what is an
4:32
instance the data present in the
4:34
database at a particular moment we call
4:36
it as an instance in relational database
4:38
we call it as relation instance what we
4:41
mean by this this relation instead sense
4:43
refers to a specific instance of a
4:45
relation it means a specific set of rows
4:48
for example if you are referring to a
4:50
specific set of rows in a relation then
4:52
this is referred as relation instance
4:55
and coming to the next important Concept
4:57
in relational database which is the
4:59
domain what is a domain it is actually a
5:03
set of permitted values I'll give you an
5:06
example let's take we are talking about
5:08
a banking database and let's assume this
5:11
banking database is a relational
5:12
database let's also assume this bank has
5:15
five branches only five branches the
5:18
branches are in New York Washington San
5:21
Francisco Chicago and Austin or whenever
5:24
we see a value in the database against
5:26
the branch then only these five values
5:30
are permitted what are the values New
5:32
York Washington San Francisco Chicago
5:34
and Austin let's say someone is trying
5:37
to insert a row into the table with the
5:40
value Los Angeles obviously Los Angeles
5:42
is not a set of permitted values because
5:44
there is no branch called Los Angeles
5:46
for that particular Bank in that case
5:49
that particular value is not belonging
5:51
to a set of values right so that is what
5:54
we call as a domain basically a domain
5:57
is a set of parameter values and please
6:00
see here an important question when a
6:03
domain is said to be atomic the answer
6:06
to this question should be known by all
6:08
database administrators because this is
6:10
going to be playing a crucial role in
6:12
relational databases so let's understand
6:14
what do you mean by atomic a domain is
6:17
said to be Atomic if the elements in the
6:20
domain are considered to be indivisible
6:23
let's say we have a column in the table
6:25
as the phone number this phone number if
6:28
it is considered as a single value then
6:31
it is an indivisible unit and we can say
6:33
that this phone number is atomic in
6:35
nature instead if we consider phone
6:37
number has multiple units like country
6:40
code area code and the local number in
6:42
that case this phone number is referred
6:44
as non-atomic so please be noted that
6:47
when a domain is said to be Atomic in
6:49
nature when the elements of the domain
6:52
are considered to be indivisible so in
6:55
the domain example we have taken Branch
6:57
name right the branch name that we have
6:59
taken our New York City Washington San
7:01
Francisco Chicago and Austin all these
7:04
are indivisible in nature so we can
7:06
quote that the values present in the
7:08
branch name is atomic in nature because
7:11
it cannot be divided further and another
7:14
important thing to note about the
7:16
relational database is this null values
7:19
what is the null value remember this
7:21
null value is not a blank value or empty
7:24
spaces or no value or no characters null
7:28
values in dbms is a special value which
7:31
represents that the value is either
7:33
unknown or that does not exist I'll give
7:36
you an example let's take if a student
7:38
has no phone number in that case we
7:41
cannot give 0 as the phone number
7:43
because 0 is not an all value at the
7:45
same time it may be added in the future
7:48
so a student who is not having a phone
7:50
number in the database the phone number
7:53
column for that particular student it
7:55
should be a null value because it is
7:58
either unknown or does not exist I will
8:01
elaborate about the concept of null
8:03
values when the course progresses and
8:05
I'll ask you a question will the
8:07
relations are generally sorted in nature
8:09
or unsorted in nature
8:11
the relations are generally unsorted in
8:14
nature the reason for this I'll explain
8:16
you in the following slides let's take
8:18
an example relation the example we are
8:21
going to take here is the instructor
8:23
relation which contains four attributes
8:25
instructor ID instructor name Department
8:28
name and salary and can you see here we
8:31
have some rows here this is actually a
8:34
tuple in relational database 34586 the
8:37
instructor ID is pertaining to John who
8:40
is working for the Department biology
8:42
who is drawing a salary of 65 000. now
8:46
the instructor ID of John is 34586 and
8:50
34586 is actually John and that's why I
8:53
told you a row in a table or a tuple in
8:56
a relation represents the relationship
8:59
among a set of values and this is about
9:02
the instructor relation I'll show you
9:05
one more relation the student relation
9:07
in the student relation we have four
9:09
attributes student ID student name
9:11
student department and the total credits
9:14
earned by the student so far we have
9:17
seen two relations instructor relation
9:19
and student relation let's assume these
9:21
two relations are a part of university
9:23
database what is a database it's a
9:25
collection of table in this case we are
9:27
assuming student table or student
9:29
relation and instructor relation are
9:31
part of university database how the
9:34
relationship between the tables or
9:35
relations are established it is also
9:38
achieved using another relation I'll
9:41
show you that now in this case we can
9:43
see that the advisor is a relation that
9:46
contains exactly two columns the student
9:48
ID and the instructor ID the advisor for
9:51
the student who is having the student ID
9:53
103 is 25252 what do we mean by this it
9:58
means I'll go to the previous slide 103
10:01
is B and the instructor for the student
10:04
B is Alia
10:07
25252 that is what is mentioned here the
10:11
student with the student ID 103 is B and
10:14
the student base advisor is alya who is
10:17
having the instructor ID 25252 and this
10:20
is how the relationship among multiple
10:22
tables or relations are maintained in
10:25
the relational database management
10:26
system
10:27
before we sign out let's see a homework
10:30
question here is the course relation
10:32
this course relation has course ID the
10:35
title the department name and credits
10:37
and what I am asking you to do is just
10:40
try to figure out the relationship
10:42
between the student relation or the
10:44
instructor relation with this course
10:46
relation
10:47
so this will definitely help you how
10:50
these relationships are maintained in
10:52
the database also I am going to answer
10:54
you one more question whether the
10:56	relations are sorted or unsorted if you
10:59	see here I have just shown you an
11:01	example where the course ID is actually
11:03	sorted here because this course ID is
11:06	actually sorted alphabetically B biology
11:09	followed by computer science followed by
11:11	electrical engineering followed by
11:13	Finance followed by history followed by
11:16	music and then physics so this is
11:18	alphabetically sorted in real time
11:21	databases need not be sorted let's say I
11:24	am going to insert a new row to this
11:26	course relation let's say the name of
11:28	the subject is cryptography and network
11:30	security and obviously it will be a part
11:33	of the computer science department but
11:36	do you think that this new row will be
11:37	inserted between this and this no and
11:41	that's why I told you in real time the
11:43	relations are not sorted in the storage
11:45	only it may not be sorted but while
11:48	displaying you can sort and display
11:51	and that's it guys I hope you guys
11:53	enjoyed this presentation and thank you
11:55	for watching
11:56	[Music]
11:57	[Applause]
11:59	[Music]