Lec-7: What is Data Independence | Logical vs. Physical Independence | DBMS

Summary

In the video 'Gate Smashers', the concept of data independence, synonymous with data abstraction, is explored. It discusses the three-schema architecture: view, conceptual, and physical levels, which shield users from direct data manipulation and storage details. The video emphasizes the importance of logical and physical data independence, allowing for changes in database structure or storage without affecting application programs. This independence ensures users can access data seamlessly, regardless of backend modifications, providing a transparent and efficient data access experience.

Takeaways

• 📚 Data independence, also known as data abstraction, is a concept that separates the user from the underlying data storage details.
• 🏛️ The three-schema architecture consists of the view level, conceptual level, and physical level, each serving a distinct purpose in database design.
• 🛠️ The purpose of these levels is to provide functionality that abstracts the user from the complexities of data storage and retrieval.
• 🔑 Data independence aims to make the user independent from the data storage details, ensuring data availability and accessibility without revealing storage mechanisms.
• 📊 Logical data independence allows changes in the conceptual schema, such as adding or removing columns, without affecting the application programs that access the data.
• 💾 Physical data independence ensures that changes in the physical storage, like moving data to a different disk or changing data structures, do not impact the conceptual schema.
• 👤 The user's demand for 24/7 data availability and accessibility is met without exposing them to the intricacies of data storage and indexing.
• 📊 Views are used to implement logical data independence by presenting a virtual table to the user that may contain only a subset of the actual columns in the database.
• 🛠️ The storage manager's role is crucial in maintaining data integrity and efficiency, using various indexes and file structures to optimize data storage and retrieval.
• 🌐 Data independence provides transparency, allowing users to interact with data as if it were local, even when it's stored remotely or has undergone structural changes.

Q & A

What is the three-schema architecture?

The three-schema architecture refers to the separation of a database into three levels: the external or view level, the conceptual level, and the internal or physical level. This architecture is designed to provide data independence and abstraction.

What is the purpose of the view level in the three-schema architecture?

The view level is the level closest to the user and provides a customized view of the data that the user needs to see, hiding the underlying complexities of the database structure.

What does the conceptual level represent in a database?

The conceptual level represents the logical structure of the database, which includes the tables, their relationships, constraints, primary keys, and foreign keys. It is an abstraction that hides the physical storage details from the users.

What is the role of the physical level in the three-schema architecture?

The physical level describes how the data is actually stored on disk, including the choice of file structures, indexes, and storage devices. Changes at this level do not affect the higher levels of the architecture.

What is data independence?

Data independence is the concept of making the user's access to data independent from the underlying data structures and storage mechanisms. It ensures that changes in the database structure do not require changes to the user's application programs.

How does logical data independence benefit application programs?

Logical data independence allows changes to be made at the conceptual level, such as adding or removing columns, without affecting the application programs that interact with the database through views.

What is the concept of views in the context of databases?

Views in databases are virtual tables that present a subset of data from one or more tables. They are used to provide a customized view of the database to users, enhancing data independence and security.

How does physical data independence protect application programs from changes in the physical schema?

Physical data independence ensures that changes in the physical storage of data, such as moving data to a different disk or changing the indexing strategy, do not impact the conceptual schema or the application programs that rely on it.

Why is it important to hide the details of the conceptual schema from users?

Hiding the details of the conceptual schema from users allows for flexibility in database design and maintenance without affecting the user's interaction with the data, thus providing a stable interface for applications.

Can you provide an example of how logical data independence is implemented in a real-world application?

In a university management system, if a new column is added to the student table, such as 'Mobile Number', this change does not require the university's application programs to be rewritten, as long as the views presented to the users are not affected.

What is the significance of data independence in the context of large-scale systems like Google's infrastructure?

Data independence is crucial for large-scale systems like Google's infrastructure because it allows for continuous changes and optimizations in the underlying data storage and retrieval mechanisms without disrupting the user experience or requiring frequent updates to the application interfaces.

Outlines

00:00

💾 Data Independence and Its Significance

The paragraph introduces the concept of data independence, which is a core aspect of database management systems. It explains that data independence is about making the user's interaction with data independent from the underlying data storage mechanisms. The video discusses the three-schema architecture: the view level, conceptual level, and physical level. Each level serves a specific purpose and functionality, and the paragraph emphasizes the importance of these levels in ensuring that users can access data without being affected by changes in the database structure or storage. The concept of logical and physical data independence is introduced, highlighting how these principles allow for flexibility in database management without disrupting user access.

05:01

🔄 Understanding Logical and Physical Data Independence

This paragraph delves deeper into the practical implications of logical and physical data independence. Logical data independence is exemplified by the ability to add or remove columns in a database table without affecting the application programs that interact with the database. The paragraph explains how views can be used to present a subset of data to users, thus hiding the underlying complexity of the database structure. Physical data independence is discussed in the context of changes to the storage and access methods of data, such as moving data between hard disks or changing indexing strategies, without impacting the higher-level schemas. The paragraph also touches on the benefits of these principles for modern applications, such as university management systems and e-commerce platforms, which can evolve without requiring frequent updates to the application code.

10:03

🌐 Data Independence in Modern Applications

The final paragraph wraps up the discussion on data independence by emphasizing its role in modern applications. It mentions how companies like Google manage vast amounts of data and undergo frequent changes in their physical and conceptual schemas without affecting the end-user experience. The paragraph reinforces the idea that data independence provides a level of transparency and convenience for users, who remain unaffected by backend changes. It concludes by summarizing the two types of data independence—logical and physical—and their importance in ensuring a seamless and efficient user experience.

Keywords

💡Data Independence

Data independence refers to the ability of a database system to minimize the impact of changes in one level of the database architecture on other levels. In the context of the video, it is about ensuring that users can access data without being affected by changes in the underlying data storage or structure. The video discusses two types of data independence: logical and physical, which together provide a layer of transparency and convenience for users accessing data.

💡Three Schema Architecture

The three schema architecture is a fundamental concept in database design that separates the database into three levels: the external (view) level, the conceptual level, and the internal (physical) level. This architecture allows for data independence by abstracting the data at different levels, as discussed in the video. The video explains that these levels are designed to serve different purposes and functionalities, enhancing the database's usability and maintainability.

💡View Level

The view level, also known as the external level, is the part of the database that users interact with directly. It represents a user's view of the data, hiding the complexities of the underlying database structure. The video uses the example of a user adding a new column, such as 'Mobile number', without affecting the existing application programs, illustrating how the view level provides logical data independence.

💡Conceptual Level

The conceptual level is the middle layer of the three-schema architecture, which provides a logical structure of the data independent of the physical storage. It includes tables, relationships, constraints, and keys. The video explains that changes at this level, such as adding or deleting a column, do not affect the view level, thus maintaining logical data independence.

💡Physical Level

The physical level is the lowest layer of the three-schema architecture and deals with how data is actually stored on disk. It includes details like file structures, indexes, and storage devices. The video emphasizes that changes at the physical level, such as moving data from one hard disk to another, do not impact the conceptual or view levels, thus providing physical data independence.

💡Logical Data Independence

Logical data independence is the concept that changes in the logical structure of the database, such as adding or removing attributes or tables, do not require changes to the application programs that access the data. The video explains this with the example of a user adding a 'Mobile number' column to a 'student' table, which does not necessitate rewriting the application program.

💡Physical Data Independence

Physical data independence ensures that changes in the physical storage of data, such as moving data to a different disk or changing the data structure, do not affect the conceptual schema or the application programs. The video uses the example of Google's storage changes over time, which do not impact the user experience or the application program.

💡Views

In the context of the video, views are virtual tables that represent a subset of data from one or more tables in the database. They are used to provide users with a customized view of the data, hiding unnecessary columns and simplifying the data access. The video explains that views are a key mechanism for implementing logical data independence, allowing users to see only the data they need.

💡Data Structures

Data structures refer to the way data is organized and stored in a database. The video mentions that changes in data structures, such as switching from a sequential search to a linked data search, can be made at the physical level without affecting the application programs. This highlights the importance of data structures in achieving physical data independence.

💡Storage Manager

The storage manager is a component of the database system responsible for managing the physical storage of data. As discussed in the video, the storage manager uses various techniques like indexing and file structures to efficiently store and retrieve data. Changes in the storage manager's operations can be made without impacting the higher levels of the database architecture, thanks to physical data independence.

💡Transparency

Transparency, in the context of the video, refers to the user's experience of seamless and uninterrupted access to data, regardless of changes in the underlying database architecture. The video explains that data independence provides transparency by allowing users to interact with the data as if it were local, even if the data is stored remotely or has undergone structural changes.

Highlights

Introduction to the concept of data independence and its importance in database management.

Explanation of the three-schema architecture: View level, Conceptual level, and Physical level.

The functionality and purpose of each level in the three-schema architecture.

The idea of data independence from the user's perspective and its benefits.

How data independence allows users to access data without knowing the underlying storage details.

The concept of logical data independence and its role in database design.

The impact of logical data independence on application programs when the database schema changes.

The use of views to implement logical data independence and their function as virtual tables.

The concept of physical data independence and its significance in database management.

How physical data independence allows changes in the physical storage without affecting the application.

The role of the storage manager in maintaining data integrity during physical schema changes.

The various data structures and access methods used in physical schema design.

The practical applications of data independence in modern web applications and databases.

The concept of transparency in data access and how data independence contributes to it.

The importance of data independence in providing a seamless user experience in applications like Gmail.

The summary of the two types of data independence: logical and physical, and their significance.

Transcripts

Hello friends, welcome to Gate Smashers

The topic is data independence

Or we can also called it data abstraction

Actually we had discus in the previous video.

Three schema architecture

What is the concept of 3 schema architecture?

Between the user and the database,

we have put three levels.

View level, Conceptual Level, physical level

What is the functionality of the all the three levels?

What is the purpose of all this three levels?

That's what we discussed in that video.

In this video we are going to discuss.

Actually what are the use of these levels?

Means, Why are we using these levels?

So that concept we called data independence.

Data Independence as its name suggest,

which means making the independent.

But from whom?

From User.

Means,

What is the basic aim of the user?

To access the data.

24×7 my data should be available.

I can access the data at any place.

I can access the data at any time.

This is, as a user, This is my demand.

Now we will fulfill the user's demand,

but here we will make the user independent.

From whom? From the data.

Means the data which we are actually storing.

Where we are storing?

How we are storing it?

Have we put an index in it?

Which index have been applied?

which data structure we have used?

All these things,

We are hiding from the user.

The second is the conceptual schema.

What does "concipual view" means?

That whatever logical structure we have used

means that we have made tables,

how many tables have been made,

what is the name of the tables,

what is the relationship between them?

What is the constraints,

what is the primary key,

what is the foreign key?

All these values,

we are hiding from the users.

Means that part of the conceptual schema,

the logical structure

which I had discussed in the previous video,

So we are not showing those details to user.

And Similarly in physical schema,

that how the data is actually stored,

that too we are hiding from the user.

So why are we hiding?

The concept is

that how the user actually access the data,

From an application program

means there is an interface,

a web application or a mobile app through .

which they are accessing the data

When the user is accessing the data,

we do not show all these things to the user.

So because of this,

actually what is the concept here,

we used two types of data independence.

Logical data independence.

Physical data independence.

What is the concept of Logical Data Independence?

If I am at the conceptual level

Means What happen at the conceptual level,

which table we are using?

How many tables are there,

how many attributes are in it?

As if there is a student table.

and in the student table,

I have name's column

Age's column.

So what have we shown to the user?

Name and Age.

Now, a user.

Let say, User 1

User 1 is adding a new column to it.

Let say, Mobile number.

So if User 1 adding this column

It will not affect the application program,

means I don't need to rewrite the entire application program.

We are giving the changes

what changes user 1 wants,

but it will not effect the actual logical structure.

That means if user 2 accessing that data.

if I had shown these two columns to user 2 earlier,

then they will still see these two columns

Because Who has made the change in this structure?

User 1.

So whatever we are changing,

that's changes we are basically keeping it,

We are showing what the user particularly wants to see.

How can we implement this?

By Using the Views.

What is the concept of views?

virtual tables means

actually we may have 50 columns in the table

but I am not showing all the columns to the user

I am showing them 5 or 7 columns,

So what makes the user thinks that,

there are that much columns

in the table or in the database.

But actually there can be a lot of

columns in the database.

So what is the concept of conceptual schema?

whatever my tables are,

whatever tables i have,

Whatever are the relationship tables between them,

the primary, Constraints,

I'm changing anything in them,

because of that change

there is no effect in the view level.

means that application is running as it is.

And this thing in today's time,

whatever application you are using,

Whether in university,

you are using UMS University Management System.

Whether you are using some shopping website,

any website if you're using

So what do you think they make

a change in the daily basis or not?

Yes, they do changes on the daily basis.

Means in structure,

they change in the logical structure.

Added a new column.

Deleted a column, added a new row,

Deleted the old row.

So that doesn't mean that

they have to rewrite the application again & again.

Web application is the same.

So what happens because of this in the data,

what advantage did i get?

Basically I can access the data

properly and conveniently.

That means I don't need to change

the application program again and again.

There will be no effect on view level.

there will be no effect on the view level for that,

What do we use?

Logical data independence

And so I have another independence

that is physical data independence

what is the concept of physical data independence?

If I am making some changes

in the physical schema.

That will not effect in conceptual schema

What I mean to say

We kept the database in hard disk 1

Now I put it in hard disk 2.

That doesn't mean name of

my tables will change,

Structure of my table will change, No.

I shifted the database at backend

in another area.

I was using a data structure, Stack

Or using any data structures.

I changed the structure and modified it.

then because of that there will be

no difference in the conceptual schema.

This means that we can use different

functionalities, Whether

I am changing the storage structure.

Storage Structure, If I'm changing,

Or am I changing a data structure?

I am modifying it Or index.

Because when we save the data,

When we do storage

What is the responsibility of the storage manager

to save the data properly,

means to save the data properly in the hard disk.

now at that time, what do they use?

Concept of many indexes used

The concept of file structure is also used

in the file structure also,

It has different method of access,

there are random access, sequential access,

linked access.

So if I'm changing all those values

Then that change Will not do any effects

in the conceptual schema.

So actually this is data indepence

means whatever application

we are using in today's time,

as many application we are using.

web application

If I'm using them on daily basis

You'll never feel it.

that whether they have changed in

conceptual schema or physical schema Or not,

because Application program is the same.

And there are no changes in the application program.

Similarly, if we see one more thing

in the physical schema

If we talk about Google,

Then they have huge amount of storage

What do you think, 10 years ago,

where the data was stored, the data is there only, No.

They must have changed at many places

and shifted a lot of data

and do lots of changes.

And if so. If i talk about the structure,

conceptual

If they are using object-oriented database.

they must have changed the name

of the object, name of the table,

structure of the table,

but that doesn't mean

It will change at the view level.

Means, Whatever we are changing

in the physical schema.

Will not effect on my conceptual schema.

And the changes made on conceptual level

Will not effect on view level.

Means my view level will be prevented.

How? Because of Logical data independence

and if I am changing in physical schema

The conceptual schema won't make any difference,

it will be prevented, how?

Because of Physical data independence

That means It's providing me a convenience

to access the data and on daily basis

We have to change the data

to bring the efficiency for fast access.

Maybe in today's time, i have a data

in which sequential search is good.

means such particular data

where if I do a sequential search,

it is working better.

But tomorrow my data should be such in

which link data search is working fast

I'll make some changes at the backend,

that doesn't mean that

Change the name of the table as well.

Change the structure of the table.

That doesn't mean that either.

to change the application program.

In this way, the user will get a new

application again and again, No.

The application we are using is as it is

Yes, if there are any changes on the backend.

This will not affect the user.

This is actual the meaning of the Data independence

and it's a way to provide transparency.

What does transparency mean?

The user is feeling,

wow my data is means my data is with me.

But actually, the data is on a remote area.

But whenever we access Gmail,

it access very fastly.

Now gmail persons

They also do changes in physical schema on a daily basis.

There is also some change in the conceptual schema,

but that will not affect at the user level.

So this is what the data independence.

There are two types Logical data independence

and physical data.

Thank you