Types of databases (relational, NoSQL, object-oriented) in DBMS Theory - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a relational database?

A relational database stores data in tables with rows and columns. Each table has a unique key, and tables can be linked using these keys. It is like a spreadsheet where data is organized and easy to find.

beginner

What does NoSQL stand for and what is its main feature?

NoSQL means 'Not Only SQL'. It stores data in flexible ways like documents, key-value pairs, or graphs instead of tables. It is good for handling large or changing data quickly.

intermediate

How does an object-oriented database store data?

An object-oriented database stores data as objects, like in programming. Each object contains data and actions. It is useful when data is complex and related to real-world objects.

beginner

Name one advantage of relational databases.

Relational databases are good at keeping data organized and consistent using rules called constraints. They make it easy to search and join data from different tables.

intermediate

Why might someone choose a NoSQL database over a relational one?

NoSQL databases are chosen when data changes often or is very large. They can handle many users and different data types faster and more flexibly than relational databases.

Which type of database stores data in tables with rows and columns?

A NoSQL database

B Relational database

C Object-oriented database

D Graph database

Relational databases organize data in tables with rows and columns.

What is a key feature of NoSQL databases?

A Strict table structure

B Uses only SQL queries

C Flexible data storage formats

D Only stores numbers

NoSQL databases store data in flexible formats like documents or key-value pairs.

Which database type stores data as objects with both data and actions?

A Hierarchical

B NoSQL

C Relational

D Object-oriented

Object-oriented databases store data as objects containing data and methods.

Which database type is best for handling large, changing data quickly?

A NoSQL

B Relational

C Object-oriented

D Flat file

NoSQL databases are designed for large and rapidly changing data.

What is a common use of relational databases?

A Organizing data with clear relationships

B Handling unstructured data

C Storing complex objects with methods

D Storing data without any structure

Relational databases organize data with clear relationships using tables.

Explain the main differences between relational, NoSQL, and object-oriented databases.

Think about how data is organized and accessed in each type.

When would you choose a NoSQL database instead of a relational database?

Consider the nature and size of the data.

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