A Uniform Resource Identifier (short: URI) is a standardised character string for uniquely identifying a resource – on the internet or beyond. URI is the umbrella term for two specialised subtypes: the URL, which also locates a resource, and the URN, which describes only its identity without specifying an access path.
Structure of a URI
A URI consists of several components:
scheme://host/path?parameter=value#anchor
- Scheme: defines how the rest of the URI is to be interpreted (e.g.
http,mailto,urn) - Host/authority: for network-based schemes, the addressed instance (e.g.
www.example.com) - Path: the concrete location of the resource within the host
- Parameters and anchor: optional additional information for more precise addressing
URI schemes at a glance
The scheme at the start of a URI determines what kind of resource is addressed:
| Scheme | Use | Example |
|---|---|---|
http / https | Web pages | https://example.com/page |
mailto | Email addresses | mailto:info@example.com |
tel | Phone numbers | tel:+491234567 |
ftp | File transfer | ftp://server.example.com/file.zip |
urn | Permanent, location-independent identifiers | urn:isbn:978-3-86680-192-9 |
URI vs. URL vs. URN
The three terms are frequently jumbled in everyday use:
- URI is the umbrella term for any unique resource identifier.
- URL is a URI that additionally describes the access path to the resource – the classic web address.
- URN is a URI that describes only a resource’s identity, independent of its current storage location.
Mnemonic: every URL and every URN is a URI, but not every URI is a URL or URN.
What URIs are used for
URIs play a central role in connecting resources, building hyperlinks and unique addressing in APIs and data formats. Beyond the pure web, URIs also serve as unique identifiers in XML namespaces, RDF data or software configuration – wherever something must be uniquely identifiable, regardless of whether it can be opened directly in a browser.
Conclusion
The URI is the conceptual roof over URLs and URNs – in everyday web life you almost exclusively encounter URLs, but the broader URI concept becomes relevant wherever resources must be uniquely identified rather than merely located. In the technical design of APIs, data structures or website architecture, we take such details into account from the start. More as part of our custom software development or in a free first conversation.
Häufige Fragen
Is every URL also a URI?
What's the difference between a URI and a URN?
Which URI schemes exist besides http and https?
mailto: for email addresses, tel: for phone numbers, ftp: for file transfer, urn: for permanent identifiers or data: for directly embedded content. Each scheme defines its own rules for how the rest of the URI is interpreted.Why does the exact distinction between URI and URL often not matter in everyday life?
Can a URI also point to a resource that isn't on the internet?
file:) or abstract, not directly retrievable identifiers like XML namespaces can also be expressed as URIs. The concept is deliberately broader than “the address of a web page”.