Types of databases (relational, NoSQL, object-oriented) in DBMS Theory - Step-by-Step Execution

Concept Flow - Types of databases (relational, NoSQL, object-oriented)

Start

↓

Choose Database Type

↓

Relational DB

↓

Tables with rows & columns

↓

NoSQL DB

↓

Flexible schema, key-value, document, graph

↓

Object-Oriented DB

↓

Store objects directly

↓

Use DB for data storage & retrieval

↓

End

This flow shows choosing between three main database types and their core characteristics before using them for data storage.

Execution Sample

DBMS Theory

SELECT * FROM Customers;
-- Relational DB query to get all customers

// NoSQL example: db.customers.find({})
// Object DB: store and retrieve objects directly

Shows example queries or actions for each database type to retrieve data.

Analysis Table

Step	Database Type	Data Structure	Query/Access Method	Example Output
1	Relational	Tables with rows and columns	SQL SELECT statements	Rows of customer data in table format
2	NoSQL	Flexible: key-value, document, graph	NoSQL queries (e.g., find())	JSON-like documents or key-value pairs
3	Object-Oriented	Objects with attributes and methods	Object methods or queries	Objects with properties and behaviors
4	End	-	-	Data retrieved according to DB type

💡 All database types provide data storage and retrieval but differ in structure and query methods.

State Tracker

Database Type	Structure	Query Method	Output Format
Relational	Tables	SQL	Rows/Columns
NoSQL	Documents/Key-Value/Graph	NoSQL Query	JSON-like or key-value
Object-Oriented	Objects	Object Methods	Objects

Key Insights - 3 Insights

Why does a relational database use tables instead of objects?

Relational databases organize data in tables with rows and columns for easy querying with SQL, as shown in execution_table row 1, unlike object databases that store data as objects.

How is NoSQL different from relational databases in data structure?

NoSQL databases use flexible structures like documents or key-value pairs (execution_table row 2), allowing schema changes without altering the whole database, unlike fixed tables in relational DBs.

What does it mean that object-oriented databases store objects directly?

It means data is stored as objects with attributes and methods (execution_table row 3), matching programming language objects, so no translation to tables is needed.

Visual Quiz - 3 Questions

Look at the execution_table, which database type uses SQL SELECT statements?

A Relational

B NoSQL

C Object-Oriented

D All of the above

💡 Hint

Check the 'Query/Access Method' column in execution_table row 1.

According to variable_tracker, which database type stores data as objects?

A Relational

B NoSQL

C Object-Oriented

D None

💡 Hint

Look at the 'Structure' column for each database type in variable_tracker.

At which step in execution_table do we see JSON-like documents as output?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Refer to the 'Example Output' column in execution_table row 2.

Concept Snapshot

Types of Databases:
- Relational: Tables with rows/columns, use SQL queries.
- NoSQL: Flexible schema, stores documents, key-value, or graphs.
- Object-Oriented: Stores objects directly with attributes/methods.
Each type suits different data and application needs.

Full Transcript

This lesson shows three main types of databases: relational, NoSQL, and object-oriented. Relational databases organize data in tables and use SQL to query data. NoSQL databases use flexible structures like documents or key-value pairs and have different query methods. Object-oriented databases store data as objects directly, matching programming language objects. The execution table shows examples of data structures, query methods, and outputs for each type. The variable tracker summarizes their key differences. Key moments clarify common confusions about data structure and query methods. The quiz tests understanding by referencing the execution visuals.

Practice

1. Which type of database stores data in tables and uses SQL for queries?

easy

A. Object-oriented database

B. NoSQL database

C. Graph database

D. Relational database

Solution

1. Step 1: Understand database types

   Relational databases organize data in tables with rows and columns.

2. Step 2: Identify query language

   They use SQL (Structured Query Language) to manage and query data.

3. Final Answer:

   Relational database -> Option D

4. Quick Check:

   Tables + SQL = Relational database [OK]

Hint: Tables and SQL mean relational database [OK]

Common Mistakes:

• Confusing NoSQL with relational because both store data
• Thinking object-oriented databases use SQL
• Assuming graph databases are relational

2. Which of the following is the correct way to describe a NoSQL database?

easy

A. Stores flexible data like documents or key-value pairs

B. Stores data only in tables with fixed schema

C. Stores data as objects matching programming languages

D. Uses only SQL for data queries

Solution

1. Step 1: Recall NoSQL database features

   NoSQL databases store data flexibly, often as documents or key-value pairs.

2. Step 2: Eliminate incorrect options

   They do not require fixed schemas or only tables, and do not rely solely on SQL.

3. Final Answer:

   Stores flexible data like documents or key-value pairs -> Option A

4. Quick Check:

   No fixed schema + flexible data = NoSQL [OK]

Hint: Flexible data storage means NoSQL [OK]

Common Mistakes:

• Thinking NoSQL uses only tables
• Confusing object-oriented with NoSQL
• Assuming NoSQL requires SQL queries

3. Given the following description, which database type fits best?
Data is stored as objects with properties and methods, similar to programming languages.

medium

A. Relational database

B. NoSQL database

C. Object-oriented database

D. Hierarchical database

Solution

1. Step 1: Analyze data storage style

   The data is stored as objects with properties and methods, matching programming language objects.

2. Step 2: Match to database type

   Object-oriented databases store data as objects, unlike relational or NoSQL databases.

3. Final Answer:

   Object-oriented database -> Option C

4. Quick Check:

   Objects with methods = Object-oriented database [OK]

Hint: Objects with methods mean object-oriented DB [OK]

Common Mistakes:

• Confusing object-oriented with NoSQL
• Thinking relational databases store objects
• Assuming hierarchical is object-oriented

4. Identify the error in this statement:
NoSQL databases always use SQL queries to retrieve data.

medium

A. No error, statement is correct

B. NoSQL databases do not use SQL queries

C. NoSQL databases only store data in tables

D. NoSQL databases are a type of relational database

Solution

1. Step 1: Understand NoSQL query methods

   NoSQL databases typically use query methods other than SQL, like JSON queries or key-value lookups.

2. Step 2: Identify the error

   The statement wrongly claims NoSQL always uses SQL, which is false.

3. Final Answer:

   NoSQL databases do not use SQL queries -> Option B

4. Quick Check:

   NoSQL ≠ SQL queries [OK]

Hint: NoSQL means no SQL queries [OK]

Common Mistakes:

• Believing NoSQL uses SQL
• Confusing NoSQL with relational
• Thinking NoSQL stores only tables

5. A company wants to store user profiles with flexible fields that can change often, and also wants to store some complex objects with methods for processing. Which combination of databases should they use?

hard

A. A NoSQL database for flexible data and an object-oriented database for complex objects

B. Only a relational database

C. Only a NoSQL database

D. Only an object-oriented database

Solution

1. Step 1: Analyze data needs

   Flexible fields suggest NoSQL for schema flexibility; complex objects with methods suggest object-oriented database.

2. Step 2: Choose suitable combination

   Using both NoSQL and object-oriented databases fits the requirements best.

3. Final Answer:

   A NoSQL database for flexible data and an object-oriented database for complex objects -> Option A

4. Quick Check:

   Flexible + complex objects = NoSQL + object-oriented [OK]

Hint: Use NoSQL for flexible, object-oriented for complex objects [OK]

Common Mistakes:

• Choosing only relational database ignoring flexibility
• Using only NoSQL and ignoring object methods
• Assuming object-oriented alone handles flexible fields