REST vs SOAP vs GraphQL comparison in Rest API - Performance Comparison

Time Complexity: REST vs SOAP vs GraphQL comparison

O(n)

Understanding Time Complexity

When comparing REST, SOAP, and GraphQL APIs, it's important to understand how their execution time grows as the amount of data or requests increase.

We want to know how the time to get data changes when the input or query size grows.

Scenario Under Consideration

Analyze the time complexity of handling data requests in REST, SOAP, and GraphQL.

// REST: GET /users/123
// SOAP: Request with XML envelope for user data
// GraphQL: query { user(id: 123) { name, posts { title } } }

// Each fetches data differently and may request more or less data
    

This shows how each API style requests data: REST uses fixed endpoints, SOAP uses XML messages, and GraphQL allows flexible queries.

Identify Repeating Operations

Look at what repeats when fetching data:

• REST: Multiple endpoints may be called separately, repeating network requests.
• SOAP: Complex XML parsing repeats for each request and response.
• GraphQL: Single request with nested fields may cause repeated data fetching inside the server.
• Primary operation: Data retrieval and parsing from server to client.
• How many times: REST and SOAP may repeat calls per resource; GraphQL tries to reduce calls but may do more work per call.

How Execution Grows With Input

As the requested data grows, the time to get it changes:

Input Size (n)	Approx. Operations
10 items	REST: ~10 calls, SOAP: ~10 XML parses, GraphQL: 1 call with nested fetches
100 items	REST: ~100 calls, SOAP: ~100 XML parses, GraphQL: 1 call with deeper nested fetches
1000 items	REST: ~1000 calls, SOAP: ~1000 XML parses, GraphQL: 1 call with heavy nested processing

Pattern observation: REST and SOAP calls grow linearly with items, while GraphQL keeps calls constant but processing inside grows with data complexity.

Final Time Complexity

Time Complexity: O(n)

This means the time to get data grows roughly in direct proportion to how much data or how many resources are requested.

Common Mistake

[X] Wrong: "GraphQL always has faster response time because it uses one request."

[OK] Correct: While GraphQL uses one request, the server may do more work inside to gather nested data, so total time can still grow with data size.

Interview Connect

Understanding how different API styles handle data requests helps you explain trade-offs clearly and shows you can think about performance in real projects.

Self-Check

"What if GraphQL queries are deeply nested with many fields? How would that affect the time complexity compared to REST?"

Practice

1. Which API style allows clients to request exactly the data they need in a single query?

easy

A. FTP

B. REST

C. SOAP

D. GraphQL

Solution

1. Step 1: Understand GraphQL's data fetching

   GraphQL lets clients specify exactly which fields they want in a query, reducing over-fetching.

2. Step 2: Compare with REST and SOAP

   REST uses fixed endpoints and HTTP methods, SOAP uses strict XML messages, neither allows flexible data selection like GraphQL.

3. Final Answer:

   GraphQL -> Option D

4. Quick Check:

   Exact data request = GraphQL [OK]

Hint: GraphQL = precise data queries in one request [OK]

Common Mistakes:

• Confusing REST with GraphQL's flexible queries
• Thinking SOAP supports flexible data selection
• Choosing unrelated protocols like FTP

2. Which of the following is the correct HTTP method typically used by REST APIs to update a resource?

easy

A. PUT

B. POST

C. GET

D. CONNECT

Solution

1. Step 1: Recall REST HTTP methods

   REST commonly uses PUT to update or replace a resource at a URL.

2. Step 2: Differentiate from other methods

   GET retrieves data, POST creates new resources, CONNECT is for network tunnels, so only PUT updates.

3. Final Answer:

   PUT -> Option A

4. Quick Check:

   Update resource = PUT [OK]

Hint: PUT method updates resources in REST [OK]

Common Mistakes:

• Using GET to update data
• Confusing POST with update instead of create
• Selecting non-REST HTTP methods like CONNECT

3. Given the following GraphQL query, what data will the client receive?

{ user(id: "123") { name email } }

medium

A. {"user": {"name": "Alice"}}

B. {"user": {"name": "Alice", "email": "[e-mail]"}}

C. {"user": {"id": "123", "name": "Alice"}}

D. {"user": {"email": "[e-mail]"}}

Solution

1. Step 1: Analyze the GraphQL query fields

   The query requests the user's name and email fields for user with id "123".

2. Step 2: Determine expected response

   The response includes both requested fields inside the user object, matching {"user": {"name": "Alice", "email": "[e-mail]"}}.

3. Final Answer:

   {"user": {"name": "Alice", "email": "[e-mail]"}} -> Option B

4. Quick Check:

   Requested fields = name and email [OK]

Hint: GraphQL returns only requested fields in response [OK]

Common Mistakes:

• Expecting all user fields returned
• Missing one of the requested fields
• Confusing id field presence

4. You have a SOAP API call that fails due to incorrect message format. What is the most likely cause?

medium

A. Using GraphQL query syntax in the request

B. Missing HTTP GET method in the request

C. Using JSON instead of XML in the request body

D. Not specifying the resource URL correctly

Solution

1. Step 1: Understand SOAP message format requirements

   SOAP requires XML formatted messages strictly following its schema.

2. Step 2: Identify common format errors

   Sending JSON instead of XML breaks the SOAP message format, causing failure.

3. Final Answer:

   Using JSON instead of XML in the request body -> Option C

4. Quick Check:

   SOAP needs XML, not JSON [OK]

Hint: SOAP messages must be XML formatted [OK]

Common Mistakes:

• Using JSON payloads with SOAP
• Confusing HTTP methods for SOAP
• Mixing GraphQL syntax with SOAP

5. You need to design an API for a mobile app that requires minimal data usage and flexible queries. Which API style is best and why?

hard

A. GraphQL, because it lets clients request exactly the data they need

B. REST, because it uses simple URLs and HTTP methods

C. SOAP, because it uses strict XML for secure communication

D. FTP, because it transfers files efficiently

Solution

1. Step 1: Identify requirements for minimal data and flexible queries

   The app needs to reduce data usage and allow clients to specify data fields.

2. Step 2: Match API styles to requirements

   GraphQL allows clients to request only needed data in one query, minimizing data transfer and providing flexibility.

3. Final Answer:

   GraphQL, because it lets clients request exactly the data they need -> Option A

4. Quick Check:

   Minimal data + flexible queries = GraphQL [OK]

Hint: Choose GraphQL for flexible, minimal data queries [OK]

Common Mistakes:

• Choosing REST without flexible data selection
• Selecting SOAP despite heavy XML overhead
• Confusing FTP with API styles