Q1. Study online banking system requirements and design an ER diagram for an Online Banking System. List and write the entities, corresponding attributes, relationships and cardinality.
Answer : -
Table Name : customer
| Field Name | Data Type | Constraint | Description |
|---|---|---|---|
| cust_id | int | Primary Key | Uniquely identify each Customer in this table |
| cust_name | varchar(100) | Name of the customer | |
| cust_address | varchar(200) | Address of the customer | |
| cust_phone | bigint | Customer's contact details | |
| cust_email | varchar(100) | Mail id of the customer | |
| PAN | varchar(12) | Customer's PAN details | |
| aadhaar_no | bigint | Aadhaar number of the customer | |
| date_of_birth | date | Customer's date of birth | |
| join_date | date | Customer's join date | |
| username | varchar(20) | Foreign Key | Login username for online banking |
Table Name : login
| Field Name | Data Type | Constraint | Description |
|---|---|---|---|
| username | varchar(20) | Primary Key | Login username for online banking |
| password | varchar(32) | Login password for online banking |
Table Name : account
| Field Name | Data Type | Constraint | Description |
|---|---|---|---|
| account_no | bigint | Primary Key | Uniquely identify each Account in this table |
| current_balance | number(20,2) | Current account balance | |
| opening_date | date | Account opening date | |
| IFSC | varchar(12) | Foreign Key | Branch identification code |
Table Name : account_holder
| Field Name | Data Type | Constraint | Description |
|---|---|---|---|
| account_no | bigint | Foreign Key | Account number |
| cust_id | int | Foreign Key | Customer identification number |
Table Name : savings
| Field Name | Data Type | Constraint | Description |
|---|---|---|---|
| interest_rate | number(4,2) | Interest rate of the account |
Table Name : current
| Field Name | Data Type | Constraint | Description |
|---|---|---|---|
| trade_license | varchar(20) | Trade license of the business | |
| business_PAN | varchar(12) | PAN details of the business |
Table Name : branch
| Field Name | Data Type | Constraint | Description |
|---|---|---|---|
| IFSC | varchar(12) | Primary Key | Uniquely identify each Branch in this table |
| branch_name | varchar(50) | Name of the branch | |
| branch_address | varchar(100) | Address of the branch | |
| branch_phone | bigint | Contact number of the branch |
Table Name : passbook
| Field Name | Data Type | Constraint | Description |
|---|---|---|---|
| account_no | bigint | Foreign Key | Account number |
| transaction_date | datetime | Date of the transaction | |
| description | varchar(50) | Description of the transaction | |
| withdrawal_amount | number(20,2) | Withdrawal amount | |
| deposit_amount | number(20,2) | Deposit amount | |
| balance | number(20,2) | balance after withdrawal or deposit |
Table Name : transaction
| Field Name | Data Type | Constraint | Description |
|---|---|---|---|
| transaction_id | bigint | Primary Key | Uniquely identify each Transaction in this table |
| transfer_date | datetime | Date of amount transfer | |
| amount | number(20,2) | Transfer amount | |
| account_no | bigint | Foreign Key | Sender account number |
| receiver_account_no | bigint | Receiver account number | |
| username | varchar(20) | Foreign Key | Login username for online banking |
Table Name : services
| Field Name | Data Type | Constraint | Description |
|---|---|---|---|
| username | varchar(10) | Foreign Key | Login username for online banking |
| message | varchar(500) | Service request/complaint | |
| message_date | date | Date of the service request/complaint |
Q2. Design the Relational Schema for the E-R diagram that you have drawn for part Question 1. The relations must be at least in 2NF. Perform the following on the relations :
a) Enter about 5 sets of meaningful data in each of the relations.
b) Identify the domain of various attributes.
c) Identify the Primary keys of all the relations.
d) Identify the Foreign keys and referential integrity constraints in the relations.
Answer : - Solves it Yourself
Q3. a) “For creating this Online Banking System as shown in Question 1, using a DBMS is better option or file management system.” Justify the statement given above.
Answer : - According to me DBMS is better than File Management System for Online Banking.
Drawbacks of File Management System
Data Redundancy - Data redundancy refers to the duplication of data, lets say we are managing the data of a Bank where a Account Holder has two Accounts. The Account Holder details in such case will be stored twice, which will take more storage than needed. Data redundancy often leads to higher storage costs and poor access time.
Data Inconsistency - Data redundancy leads to data inconsistency, lets take the same example that we have taken above - a Account Holder has two Accounts and we stored the Account Holder's address twice, now lets say the Account Holder requests to change his address, if the address is changed at one place and not on all the records then this can lead to data inconsistency.
Data Isolation - Because data are scattered in various files, and files may be in different formats, writing new application programs to retrieve the appropriate data is difficult.
Dependency on Application Programs - Changing files would lead to change in application programs.
Atomicity Issues - Atomicity of a transaction refers to “All or nothing”, which means either all the operations in a transaction executes or none.
For example: Lets say Rohit transfers Rs. 100/- to Amit’s account. This transaction consists multiple operations such as debit Rs. 100/- from Rohit’s account, credit Rs. 100/- to Amit’s account. Like any other device, a computer system can fail. Lets say it fails after first operation, then in that case Rohit’s account would have been debited by Rs. 100/- but the amount was not credited to Amit’s account, in such case the rollback of operation should occur to maintain the atomicity of transaction. It is difficult to achieve atomicity in File Management Systems.
Data Security - Data should be secured from unauthorised access, for example a Account Holder in a Bank should not be able to see the payroll details of the Bank Employees, such kind of security constraints are difficult to apply in File Management Systems.
Advantage of DBMS over File Management System
No Redundant Data - Redundancy removed by data normalization in DBMS. Normalization is a process of organizing the data in database to avoid data redundancy
Data Consistency and Integrity - The main cause of data inconsistency is data redundancy. Since data normalization takes care of the data redundancy, data inconsistency also been taken care of as part of it
Data Security - It is easier to apply access constraints in database systems so that only authorized user is able to access the data. Each user has a different set of access thus data is secured from the issues such as identity theft, data leaks and misuse of data.
Data Sharing - File system does not allow sharing of data or sharing is too complex. Whereas in DBMS, data can be shared easily due to centralized system.
Data Concurrency - Concurrent access to data means more than one user is accessing the same data at the same time. Anomalies occur when changes made by one user gets lost because of changes made by other user. File system does not provide any procedure to stop anomalies. Whereas DBMS provides a locking system to stop anomalies to occur.
Data Searching - For every search operation performed on file system, a different application program has to be written. While DBMS provides inbuilt searching operations. User only have to write a small query to retrieve data from database.
Data Integrity - There may be cases when some constraints need to be applied on the data before inserting it in database. The file system does not provide any procedure to check these constraints automatically. Whereas DBMS maintains data integrity by enforcing user defined constraints on data by itself.
Easy Recovery - Since database systems keeps the backup of data, it is easier to do a full recovery of data in case of a failure.
Q3. b) Talk to any Database Administrator (DBA) of any good s/w company and try to list all the key responsibilities that he have to handle in the said company.
Answer : - A database administrator’s (DBA) primary job is to ensure that data is available, protected from loss and corruption, and easily accessible as needed.
Functions/Roles of a Database Administrator (DBA) -
Deciding the Hardware Device - Depending upon the cost, performance and efficiency of the hardware, it is DBA who have the duty of deciding which hardware device will suit the company requirement. It is hardware that is an interface between end users and database so it needed to be of best quality.
Software installation and Maintenance - DBA is responsible for installing the database software. He configure the software of database and then upgrades it if needed. There are many database software like oracle, Microsoft SQL, MySQL etc. in the industry so DBA decides how the installing and configuring of these database software will take place.
If a new server is needed, the DBA handles the transfer of data from the existing system to the new platform.
Managing Data Integrity - Data integrity should be managed accurately because it protects the data from unauthorized use. DBA manages relationship between the data to maintain data consistency.
Database Backup and Recovery - If any company is having a big database, then it is likely to happen that database may fail at any instance. It is require that a DBA takes backup of entire database in regular time span. DBA has to decide that how much data should be backed up and how frequently the backup should be taken. Also the recovery of data base is done by DBA if they have lost the database.
Tuning Database Performance - Database performance plays an important role for any business. If user is not able to fetch data speedily then it may loss company business. So by tuning an modifying sql commands a DBA can improves the performance of database.
Capacity Planning - All the databases have their limits of storing data in it and the physical memory also has some limitations. DBA has to decide the limit and capacity of database and all the issues related to it.
Database Accessibility - DBA writes subschema to decide the accessibility of database. He decides the users of the database and also which data is to be used by which user. No user has to power to access the entire database without the permission of DBA.
Security - A DBA needs to know potential weaknesses of the database software and the company’s overall system and work to minimise risks. No system is one hundred percent immune to attacks, but implementing best practices can minimise risks.
In the case of a security breach or irregularity, the DBA can consult audit logs to see who has done what to the data. Audit trails are also important when working with regulated data.
Decides Validation Checks on Data - DBA has to decide which data should be used and what kind of data is accurate for the company. So he always puts validation checks on data to make it more accurate and consistence.
Performance Monitoring - Monitoring databases for performance issues is part of the on-going system maintenance a DBA performs. If some part of the system is slowing down processing, the DBA may need to make configuration changes to the software or add additional hardware capacity.
Q4. Given the relational schema:
Suppliers (s_id:integer, s_name:string, s_address:string)
Parts (p_id:integer, p_name:string, p_color:string)
Catalog (s_id:integer, p_id:integer, p_cost:real)
Write SQL statements for the following :
(i) List all the suppliers who supply the part with p_id=32.
Answer : - SELECT Suppliers.s_id, s_name, s_address FROM Suppliers, Catalog WHERE Suppliers.s_id=Catalog.s_id AND p_id=32;
(ii) List the parts whose colour is BLUE.
Answer : - SELECT p_id, p_name FROM Parts WHERE p_color='BLUE';
(iii) List those parts which are RED and whose cost is more than Rs.2000/- .
Answer : - SELECT Parts.p_id, p_name FROM Parts, Catalog WHERE Parts.p_id=Catalog.p_id AND p_color='RED' AND p_cost>2000;
(iv) List all the suppliers who are from GUJARAT.
Answer : - SELECT s_id, s_name FROM Suppliers WHERE s_address='GUJARAT';
(v) List all the part_ids, colour, cost from the supplier EZPREX.
Answer : - SELECT DISTINCT Parts.p_id, p_color, p_cost FROM Suppliers, Parts, Catalog WHERE Parts.p_id=Catalog.p_id AND Supliers.s_id=Catalog.s_id AND s_name='EZPREX';
(vi) List the cost of the part_id=41.
Answer : - SELECT DISTINCT p_cost FROM Catalog WHERE p_id=41;
Q5. Discuss all the file organization techniques with suitable examples.
Answer : - The File is a collection of records. Using the primary key, we can access the records. The type and frequency of access can be determined by the type of file organization which was used for a given set of records.
File organization is a logical relationship among various records. This method defines how file records are mapped onto disk blocks.
File organization is used to describe the way in which the records are stored in terms of blocks, and the blocks are placed on the storage medium.
Objective of File Organization
- It contains an optimal selection of records, i.e., records can be selected as fast as possible.
- To perform insert, delete or update transaction on the records should be quick and easy.
- The duplicate records cannot be induced as a result of insert, update or delete.
- For the minimal cost of storage, records should be stored efficiently.
Types of file organization
File organization contains various methods. These particular methods have pros and cons on the basis of access or selection. In the file organization, the programmer decides the best-suited file organization method according to his requirement.
Types of file organization are as follows :
- Sequential File Organization
- Heap File Organization
- Hash File Organization
- B+ Tree File Organization
- Indexed Sequential Access Method (ISAM)
- Cluster File Organization
Sequential File Organization - This method is the easiest method for file organization. In this method, files are stored sequentially. This method can be implemented in two ways :
Pile File Method
It is a quite simple method. In this method, we store the record in a sequence, i.e., one after another. Here, the record will be inserted in the order in which they are inserted into tables.
In case of updating or deleting of any record, the record will be searched in the memory blocks. When it is found, then it will be marked for deleting, and the new record is inserted.
Starting of the File → R1 R3 ---------- R8 R5 ← End of the File Suppose we want to insert a new record R2 in the sequence given above, then it will be placed at the end of the file.
Starting of the File → R1 R3 ---------- R8 R5 ← R2 Starting of the File → R1 R3 ---------- R8 R5 R2 ← End of the File Sorted File Method
In this method, the new record is always inserted at the file's end, and then it will sort the sequence in ascending or descending order. Sorting of records is based on any primary key or any other key.
In the case of modification of any record, it will update the record and then sort the file, and lastly, the updated record is placed in the right place.
Starting of the File → R1 R3 ---------- R8 R9 ← End of the File Suppose a new record R2 has to be inserted in the sequence given above, then it will be inserted at the end of the file, and then it will sort the sequence.
Starting of the File → R1 R3 ---------- R8 R9 ← R2 Starting of the File → R1 R2 R3 ---------- R8 R9 ← End of the File
Advantages of Sequential File Organization
- It contains a fast and efficient method for the huge amount of data.
- In this method, files can be easily stored in cheaper storage mechanism like magnetic tapes.
- It is simple in design. It requires no much effort to store the data.
- This method is used when most of the records have to be accessed like grade calculation of a student, generating the salary slip, etc.
- This method is used for report generation or statistical calculations.
Disadvantages of Sequential File Organization
- It will waste time as we cannot jump on a particular record that is required but we have to move sequentially which takes our time.
- Sorted file method takes more time and space for sorting the records.
Heap File Organization - Heap File Organization works with data blocks. In this method records are inserted at the end of the file, into the data blocks. No Sorting or Ordering is required in this method. If a data block is full, the new record is stored in some other block, Here the other data block need not be the very next data block, but it can be any block in the memory. It is the responsibility of DBMS to store and manage the new records.
Suppose we have five records R1, R4, R5, R3 and R8 in a heap and suppose we want to insert a new record R2 in a heap. If the last data block that is data block 3 is full then it will be inserted in any of the data block selected by the DBMS, let's say data block 1.
If we want to search, update or delete the data in heap file organization, then we need to traverse the data from staring of the file till we get the requested record.
If the database is very large then searching, updating or deleting of record will be time-consuming because there is no sorting or ordering of records. In the heap file organization, we need to check all the data until we get the requested record.
Advantages of Heap File Organization
- Fetching and retrieving records is faster than sequential record but only in case of small databases.
- When there is a huge number of data needs to be loaded into the database at a time, then this method of file Organization is best suited.
Disadvantages of Heap File Organization
- This method is inefficient for the large database because it takes time to search or modify the record.
Hash File Organization - Hash File Organization uses the computation of hash function on some fields of the records. The hash function's output determines the location of disk block where the records are to be placed.
For example, let us consider the following table Student;
| Student_id | Name | Age | Phone |
|---|---|---|---|
| 1001 | Amit Das | 40 | 9748516231 |
| 1005 | Sohini Das | 32 | 9073919231 |
| 1008 | Debabrata Panchadhyay | 29 | 8420392064 |
A hash function is a function which maps the large set of values into smaller set of files/locations/values. Let us organize the above table using the phone attribute value as input for the hash function.
Consider that the Hash Function for the Student table is → h(s_id mod 5)
In the above hash function, s_id is the Student_id attribute’s value of each record. 5 is the number of buckets/pages where we want to store our table. [5 buckets means bucket0, bucket1, . . . , bucket4].
For our example,
For 1st record, h(1001 mod 5) = 1 that is, the first record has to be stored in 1st bucket.
For 2nd record, h(1005 mod 5) = 0 that is, the second record has to be stored in 0th bucket.
For 3rd record, h(1008 mod 5) = 3 that is, the third record has to be stored in 3rd bucket.
Important points for consideration
- If bucket(s) is/are full, then overflow buckets can be used to store more records.
- Hash function has to be chosen with extra care to avoid uneven distribution. That is, a bad hash function may assign more records to few buckets and less to others.
- The attribute(s) that is frequently used for data manipulation can be chosen as the input for the hash function.
- Same hash function that was used to store the records has to be used for deletion, modification or selection of records.
Insert Record - When a new record has to be inserted, then the address is generated using the hash key and record is directly inserted.
Let us assume that the following query is executed.
INSERT INTO Student VALUES(1007, 'Payel Chatterjee', 28, 9073456582);
We use the same hash function to insert the record.
h(1007 mod 5) = 2.
Searching Record - When a record needs to be searched, The same hash function is used to retrieve the bucket address for the record.
Let us assume that the following query is executed.
SELECT * FROM Student WHERE Student_id = 1008;
For searching the record, we have to use the same hash function that we used for storing the records. Hence, h(1008 mod 5) = 3. And the result points to the 3rd bucket. It actually gives us the quick access to the required record.
Advantages of Hash File Organization
- Quick access to records in terms of selection. [If queried on the attribute that was used for hashing]
- Easy to insert, delete, or update a record.
Disadvantages of Hash File Organization
- Records are randomly stored in scattered locations. May waste a lot of space in case of small files.
- For queries that involve ranges, hash file organization is not efficient. [Example - SELECT * FROM Employee WHERE Salary BETWEEN 10000 AND 25000;]
- If querying attribute is not the hashed attribute, you may need to scan the entire table for retrieval.
- Frequent update to the hashed column results in movement of data between buckets which actually affects the system performance.
B+ Tree File Organization - B+ tree file organization is the advanced method of an indexed sequential access method. It uses a tree-like structure to store records in File. It uses the same concept of key-index where the primary key is used to sort the records. For each primary key, the value of the index is generated and mapped with the record.
The B+ tree is similar to a binary search tree (BST), but it can have more than two children. In this method, all the records are stored only at the leaf node. Intermediate nodes act as a pointer to the leaf nodes. They do not contain any records.
Advantages of Hash File Organization
- In this method, searching becomes very easy as all the records are stored only in the leaf nodes and sorted the sequential linked list.
- Traversing through the tree structure is easier and faster.
- The size of the B+ tree has no restrictions, so the number of records can increase or decrease and the B+ tree structure can also grow or shrink.
Disadvantages of Hash File Organization
- This method is inefficient for the static tables
Indexed Sequential Access Method (ISAM) - ISAM method is an advanced sequential file organization. In this method, records are stored in the file using the primary key. An index value is generated for each primary key and mapped with the record. This index contains the address of the record in the file.
If any record has to be retrieved based on its index value, then the address of the data block is fetched and the record is retrieved from the memory.
Advantages of Indexed Sequential Access Method
- In this method, each record has the address of its data block, searching a record in a huge database is quick and easy.
- This method supports range retrieval and partial retrieval of records. Since the index is based on the primary key values, we can retrieve the data for the given range of value. In the same way, the partial value can also be easily searched, i.e., the student name starting with 'JA' can be easily searched.
Disadvantages of Indexed Sequential Access Method
- This method requires extra space in the disk to store the index value.
- When the new records are inserted, then these files have to be reconstructed to maintain the sequence.
- When the record is deleted, then the space used by it needs to be released. Otherwise, the performance of the database will slow down.
Cluster File Organization - When the two or more records are stored in the same file, it is known as clusters. These files will have two or more tables in the same data block, and key attributes which are used to map these tables together are stored only once. This method reduces the cost of searching for various records in different files.
The cluster file organization is used when there is a frequent need for joining the tables with the same condition. These joins will give only a few records from both tables. In the given example, we are retrieving the record for only particular departments. This method can't be used to retrieve the record for the entire department.
Table Name : employee
| emp_id | emp_name | emp_age | dept_id |
|---|---|---|---|
| 1001 | Amit Das | 40 | 102 |
| 1005 | Sohini Das | 32 | 105 |
| 1008 | Debabrata Panchadhyay | 29 | 102 |
| 1010 | Manirash Das | 28 | 103 |
| 1012 | Payel Chatterjee | 28 | 105 |
Table Name : department
| dept_id | dept_name |
|---|---|
| 102 | JAVA |
| 103 | HTML & CSS |
| 105 | PHP |
Cluster Key : dept_id
| dept_id | dept_name | emp_id | emp_name | emp_age |
|---|---|---|---|---|
| 102 | JAVA | 1001 | Amit Das | 40 |
| 1008 | Debabrata Panchadhyay | 29 | ||
| 103 | HTML & CSS | 1010 | Manirash Das | 28 |
| 105 | PHP | 1005 | Sohini Das | 32 |
| 1012 | Payel Chatterjee | 28 |
In this method, we can directly insert, update or delete any record. Data is sorted based on the key with which searching is done. Cluster key is a type of key with which joining of the table is performed.
Types of Cluster File Organization
Indexed Clusters - In indexed cluster, records are grouped based on the cluster key and stored together. The above EMPLOYEE and DEPARTMENT relationship is an example of an indexed cluster. Here, all the records are grouped based on the cluster key - dept_id and all the records are grouped.
Hash Clusters - It is similar to the indexed cluster. In hash cluster, instead of storing the records based on the cluster key, we generate the value of the hash key for the cluster key and store the records with the same hash key value.
Advantages of Cluster File Organization
- The cluster file organization is used when there is a frequent request for joining the tables with same joining condition.
- It provides the efficient result when there is a 1:M mapping between the tables.
- The size of the B+ tree has no restrictions, so the number of records can increase or decrease and the B+ tree structure can also grow or shrink.
Disadvantages of Cluster File Organization
- This method has the low performance for the very large database.
- If there is any change in joining condition, then this method cannot use. If we change the condition of joining then traversing the file takes a lot of time.
- This method is not suitable for a table with a 1:1 condition.
Q6. a) Discuss the ACID properties of a database transaction with appropriate examples.
Answer : - A transaction in a database system must maintain Atomicity, Consistency, Isolation, and Durability − commonly known as ACID properties − in order to ensure accuracy, completeness, and data integrity.
Atomicity - A transaction must be fully complete, saved (committed) or completely undone (rolled back). A sale in a retail store database illustrates a scenario which explains atomicity, e.g., the sale consists of an inventory reduction and a record of incoming cash. Both either happen together or do not happen - it's all or nothing.
Consistency - The transaction cannot break the database’s constraints. For example, if a database table’s Phone Number column can only contain numerals, then consistency dictates that any transaction attempting to enter an alphabetical letter may not commit.
Isolation - A transaction should not make its updates visible to other transactions until it is committed; this property, when enforced strictly, solves the temporary update problem and makes cascading rollbacks of transactions unnecessary.
Durability - When a transaction has made a change to the database state and the change is committed, this change is permanent and should be available to all other transactions.
Q6. b) How are views created and dropped? Explain, how the views are implemented and updated?
Answer : - A view is a virtual or logical table that allows to view or manipulate parts of the tables. Views are useful for security of data.
Syntax :
CREATE or REPLACE VIEW view_name AS SELECT column_name(s) FROM table_name(s) WHERE condition;
A view can be dropped using a DROP statement as :
DROP VIEW view_name;
There are many advantages using view :
Security - Each user can be given permission to access the database only through a small set of views that contain the specific data the user is authorized to see, thus restricting the user's access to stored data.
Query Simplicity - A view can draw data from several different tables and present it as a single table, turning multi-table queries into single-table queries against the view.
Consistency - A view can present a consistent, unchanged image of the structure of the database, even if the underlying source tables are split, restructured, or renamed.
Data Integrity - If data is accessed and entered through a view, the DBMS can automatically check the data to ensure that it meets the specified integrity constraints.
Example :
A student''s database may have the following tables :
student ( name, enrolment_no, date_of_birth )
marks ( enrolment_no, subject_code, marks )
CREATE VIEW subject_performance AS SELECT s.enrolment_no, name, subject_code, marks FROM student AS s, marks AS m WHERE s.enrolment_no=m.enrolment_no AND subject_code='MCS-043' ORDER BY s.enrolment_no;
Once a view has been created, it can be queried exactly like a base table. For example :
Find the student details who get 40% marks or above
SELECT * FROM subject_performance WHERE marks >= 40;
Find the student details who get the highest marks.
SELECT enrolment_no, name, MAX(marks) FROM subject_performance;
Q6. c) Discuss 3-tier architecture with necessary diagram and suggest an example application for the real world domain.
Answer : - A 3-tier architecture is a type of software architecture which is composed of three “tiers” or “layers” of logical computing. They are often used in applications as a specific type of client-server system. 3-tier architectures provide many benefits for production and development environments by modularizing the user interface, business logic, and data storage layers. Doing so gives greater flexibility to development teams by allowing them to update a specific part of an application independently of the other parts.
Presentation Tier - The presentation tier is the front end layer in the 3-tier system and consists of the user interface. This user interface is often a graphical one accessible through a web browser or web-based application and which displays content and information useful to an end user. This tier is often built on web technologies such as HTML5, JavaScript, CSS, or through other popular web development frameworks, and communicates with others layers through API calls.
Business Logic or Application Tier - This layer contains the business logic that drives the application’s core functionalities. Like making decisions, calculations, evaluations, and processing the data passing between the other two layers. It’s often written in Java, .NET, C#, Python, C++, etc.
Data Tier - This layer is responsible for interacting with database/data storage system to save and restore application data. Examples of such systems are MySQL, Oracle, PostgreSQL, Microsoft SQL Server, MongoDB, etc. Data is accessed by the application layer via API calls.
3-Tier Architecture Example in Real World - A simple example of a 3-tier architecture in action would be logging into a media account such as Netflix and watching a video. You start by logging in either via the web or via a mobile application. Once you’ve logged in you might access a specific video through the Netflix interface which is the presentation tier used by you as an end user. Once you’ve selected a video that information is passed on to the application tier which will query the data tier to call the information or in this case a video back up to the presentation tier. This happens every time you access a video from most media sites.