welcome all of you to this course on fundamentals of database systems this is mostly an undergraduate

course for computer science and engineering as well as for information technology students

so let us start off with what do we mean by a database so a database is essentially a

collection of data but very importantly it is not any data it is a collection of inter

related data so the data fields or the data points must have some connections with them

so it's a set of inter related data for example I mean we all have some idea of what databases

are and where it can be used for example in an institute the entire records about an institute

constitutes one database so it will have different entities such as faculty members students

staff etc as well as other kinds of things such as courses etc and everything constitutes

one database so this is what is a database and what is a database management system or

a dbms it is a system that provides an environment to handle a database so it must be efficient

and convenient to use and essentially it contains some programs and interface to store data

so the first point is for store data that is number one number two is it must be able

to visualize data then access data or access or what is also known as querying the data

and the fourth one is update or manipulate the data so these are the four tasks of a

database management system so this is over the database the question comes then is that

the normal file system can also do all of these things It can of course store data so

we store files etc it can visualize data so well it is not really clear what does visualization

mean we will see that later but you can at least see what the files and folders are etc

it can of course access data you can access a particular file within a particular folder

etc and it lets you update the contents of the file contents of the folder etc so how

is database more important or how is it first of all different from a file how is it more

important than a file system so there is this different advantages of the file system that

let us go through so advantages of dbms over file systems

so the first one is that it reduces the data redundancy and inconsistency problems so redundancy

stroke inconsistency so let me go over each of these points a little bit so what does

data redundancy mean essentially data redundancy means the following is that there is a same

piece of data the same information that is stored in multiple places and database I mean

a well designed database does not really allow that so if there is an employee or if there

is information about a student the name of the student for example the roll number etc

is generally should be stored in only one place this is the big difference about file

system where most of us replicate files copy files from here to there etc etc what does

that copying also does is that it runs into this problem of inconsistency so what does

inconsistency actually mean is that you have two versions of a file and in one version

you have changed something and you have inadvertently forgot to make the same modification to the

other file or there are two other two people making two different versions of the file

etc so they so the information on these files two files may be inconsistent so one of them

may not be correct because the other one has been updated and the update has not yet come

to this piece so database by virtue of storing each piece of information once and in one

place reduces this inconsistency so there is no redundancy and there is no inconsistency

so that's the first point the second point is it is a very related point it is called

data isolation so here what happens is that the data is isolated

in the form that there is only one so the data is stored in an internal format and there

is only one interface to access the data so that essentially the data is stored in some

kind of a binary format which is not the headache of the final user the user wants the piece

of data and there is an interface the database interface will let that user access the data

in a particular format so the other interesting the other important advantage of this is that

because the data is isolated and stored in a format that database handles this this problem

of formatting of data is not there and this we often run into with file systems for example

you may be working with an excel file which is a spreadsheet and once you take it to for

example linux system or mac system that excel file may not open correctly because it is

not in that open document format and all those things and the and the and the and the programs

to open them does not behave consistently that's the problem but the database isolates

that the third important thing is called data integrity so what does data integrity mean

essentially is that there are many pieces of data where there is schematics of data

or there is a correctness condition for example is that the cpi or the cumulative point average

or your marks etc must be the grade point average whatever you call it they are generally

constant to be between zero to ten in our Indian systems at least but suppose you are

storing all of information in a file or in an excel spreadsheet or whatever now there

is no check so if you for example by chance entered somebody's cpi as minus one or twelve

there is no check in when you try to put in the data however a database will let you put

in some integrity constants so whenever you define the cpi field you can say that it is

between zero to ten and so any attempts to enter a data value of for example minus one

will result in a nil error and it will not let you enter the logic is in the database

system itself not by the access so once you define the database of that cpi you can say

that it is between zero to ten and then that logic is within the database system so this

is the third point the fourth point is called the atomicity of operations so this is probably

one of the most famous uses of database and as an example let us take the bank transfer

case so certain amount of money so let us say one hundred rupees is transferred from

person a account to person b account the atomicity of operations so the atomicity of transactions

defines that either the money is transferred completely or no money is transferred at all

so what do we mean by that is that it cannot happen that rupees hundred has been deducted

from a's account but it has not been credited to b's account or the other way around that

rupees hundred has been credited to b's account but it has not been debited from a's account

and you can see what problems will happen if this I mean inconsistent credits and debits

can take place so a database system encodes that entire operation of debiting from a's

account and crediting to b's account as one operation or one transaction and we will see

more about transactions later in the course and one transaction and it mandates the atomicity

of it so either this has happened completely so either one hundred has been debited and

credited both or it has not been debited credited either so this is the other important part

let us come to the fifth point the fifth point is concurrency so very simply concurrency

means multiple operations can take place together in the database the database is I mean generally

takes care of those things as long as there are no conflicts in that particular data item

so if a is transferring money to b and c is transferring money to d they do not need to

wait for each other and both the transactions can happen together in file systems or it

may not happen if all the transactions are opened in the same file so one file the same

file needs to be first edited for a to b then saved and then c to d should happen but it

depends also on the file system that is being used probably the last important thing about

databases or why it is useful over file system is that of security so

security of the data is paramount in databases and the database or the data fields can be

made secure in multiple ways so first of all for example the employee database is secured

in the sense that unauthorized users may not gain access to any of this so that is one

part of the security the other and probably the more important part of the security is

that an employee so there are different access control levels in the database for different

fields and different roles for example an employee may be able to see her own record

but not records of others it may happen that way it may also happen that student may see

a cpi of herself but not of others but a student may change her address home address but not

her cpi so even if the student even if the record is about the student so even within

a record there can be attribute level security attribute level access privileges etc and

the security mandates that nobody I mean unless it is allowed by the database system and these

roles have to be defined very carefully while defining the fields of the database will be

allowed to change that these are the six important points for the advantages of dbms over the

file systems as you go over it the first one is redundancy or inconsistency then it is

data isolation then it is data integrity the fourth one is atomicity of operations fifth

one is concurrency and the sixth one is security so well that ends the first part of the module

in the next module we will cover we will start on with the relational data models