Define URL. Explain types of URL
SOLUTION
URL — Detailed Explanation
A URL (Uniform Resource Locator) is the address used to locate and retrieve a resource on the internet. It tells a client (browser, API client, etc.) what protocol to use, which host to contact, where the resource lives, and optionally how to pass extra data or jump to a fragment inside the resource.
Components of a URL
Example URL:
Breakdown:
Scheme (protocol):
https— how to access the resource (HTTP over TLS here).User info (optional):
user:pass— username/password (discouraged in practice).Host (domain or IP):
example.com— identifies the server.Port (optional):
:8080— TCP port; default ports are implied (HTTP 80, HTTPS 443).Path:
/dir/sub/page.html— location of the resource on the server.Query string:
?q=search+term&lang=en— key/value data sent to the server (commonly for GET requests).Fragment:
#section2— a client-side anchor; not sent to server (used to jump to a part of the resource).
Types of URLs (with examples)
1. Absolute URL
A complete URL including scheme and host.
Example:
https://www.example.com/about/index.htmlUse when linking to resources on other sites or when you need a full address.
2. Relative URLs
Paths relative to the current document or site. They do not include scheme/host.
Document-relative (path-relative):
images/pic.jpgIf current page is
https://site.com/dir/page.html, this resolves tohttps://site.com/dir/images/pic.jpg.
Root-relative:
/images/pic.jpgResolves to
https://site.com/images/pic.jpgregardless of current page path.
Parent-relative:
../assets/style.cssMoves up a directory before resolving.
3. Protocol-relative URL
Starts with // and inherits the current page’s protocol.
Example:
//cdn.example.com/lib.jsIf the page is
https, this becomeshttps://cdn.example.com/lib.js.
4. Data URL
Embeds data directly in the URL (useful for small inline images).
Example:
data:text/plain;base64,SGVsbG8sIHdvcmxkIQ==
5. File URL
References local filesystem resources (used locally or in some apps).
Example:
file:///C:/Users/name/document.txtorfile:///home/user/doc.txt
6. Mailto, Tel, FTP and other scheme URLs
mailto:for email links:mailto:someone@example.comtel:for phone links on mobile:tel:+911234567890ftp:FTP resources:ftp://ftp.example.com/pub/file.zip
These use schemes other than HTTP/HTTPS and are handled accordingly.
How Relative URLs are Resolved
Browsers compute the full URL using the base URL (the current page’s URL or the <base> tag if present).
Examples (base https://site.com/dir/page.html):
images/pic.jpg→https://site.com/dir/images/pic.jpg../img/logo.png→https://site.com/img/logo.png/css/style.css→https://site.com/css/style.css
Query Strings and Fragments
Query string (
?key=value&k2=v2) passes parameters to the server; commonly used in GET requests and RESTful filtering.Fragment (
#anchor) is handled client-side (scrolling to an element, single-page app routing) and is not sent to the server.
URL Encoding (Percent-encoding)
Characters not allowed in URLs (spaces, <, >, non-ASCII, etc.) must be encoded:
Space →
%20(or+in some query contexts)Example:
https://site.com/search?q=hello%20world
Use encoding to avoid ambiguity and to safely include special characters.
Security & Best Practices
Prefer HTTPS to protect data in transit.
Do not include sensitive data (passwords, tokens, credit-card info) in URLs — query strings are logged and cached.
Use canonical URLs to avoid duplicate content issues (important for SEO).
Limit URL length (some servers/browsers have practical limits).
Validate and sanitize URL-derived input on the server to prevent injection attacks.
URL vs URI (brief)
URI (Uniform Resource Identifier) is a broader term that identifies a resource; a URL is a type of URI that gives a location you can retrieve the resource from.