Resource identifiers in URLs in Rest API - Step-by-Step Execution

Concept Flow - Resource identifiers in URLs

Client sends request

↓

URL contains resource ID

↓

Server extracts ID from URL

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Server finds resource by ID

↓

Server sends resource data back

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Client receives specific resource

The client sends a request with a URL containing a resource ID; the server extracts this ID to find and return the specific resource.

Execution Sample

Rest API

GET /users/42 HTTP/1.1
Host: example.com

Response:
HTTP/1.1 200 OK
Content-Type: application/json

{
  "id": 42,
  "name": "Alice"
}

This request asks the server for the user with ID 42, and the server responds with that user's data.

Execution Table

Step	Action	URL Part	Extracted ID	Server Operation	Response
1	Client sends request	/users/42	42	Extract ID 42 from URL	Waiting
2	Server looks up resource	/users/42	42	Find user with ID 42	User data found
3	Server sends response	/users/42	42	Send user data in response	{"id":42,"name":"Alice"}
4	Client receives response	/users/42	42	Display user data	User info shown

💡 Request completed after server sends user data for ID 42

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
URL	N/A	/users/42	/users/42	/users/42	/users/42
Extracted ID	None	42	42	42	42
Server Resource	None	None	User object with ID 42	User object with ID 42	User object with ID 42
Response	None	None	None	{"id":42,"name":"Alice"}	{"id":42,"name":"Alice"}

Key Moments - 3 Insights

Why does the server need to extract the ID from the URL?

The server extracts the ID (see Step 1 in execution_table) to know exactly which resource the client wants, so it can find and return the correct data.

What happens if the ID in the URL does not exist on the server?

If the ID is not found (not shown in this trace), the server would respond with an error like 404 Not Found instead of user data.

Can the resource identifier be something other than a number?

Yes, resource IDs can be strings or other formats, but the server must still extract and use them to find the resource.

Visual Quiz - 3 Questions

Look at the execution_table, what is the Extracted ID at Step 2?

A None

B 42

C /users/42

D User object

💡 Hint

Check the 'Extracted ID' column in row for Step 2 in execution_table.

At which step does the server send the user data back to the client?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Response' column in execution_table to find when data is sent.

If the URL was /users/99 and user 99 does not exist, what would change in the execution_table?

A Server operation would result in error, response would be 404

B Extracted ID would be None

C Server would find user 99 and send data

D Client would not send request

💡 Hint

Think about what happens when the server cannot find the resource by ID.

Concept Snapshot

Resource identifiers in URLs specify which item the client wants.
The server extracts this ID from the URL path.
It uses the ID to find the resource in its data.
The server returns the resource data in the response.
If not found, server returns an error like 404.
Example: GET /users/42 fetches user with ID 42.

Full Transcript

This visual trace shows how resource identifiers in URLs work in REST APIs. The client sends a request with a URL containing an ID, like /users/42. The server extracts the ID '42' from the URL to know which user to find. It then looks up the user with ID 42 in its data. After finding the user, the server sends back the user's data in the response. The client receives and displays this data. If the ID does not exist, the server would respond with an error such as 404 Not Found. This process helps clients get specific resources by using clear, simple URLs.