---
title: Uniform Resource Identifiers
TARGET DECK: Obsidian::STEM
FILE TAGS: uri
tags:
  - rdf
  - uri
---

## Overview

A **uniform resource identifier** (URI) is a unique sequence of characters for identifying some physical or abstract resource. URIs are further generalized to **internationalized resource identifier**s (IRIs) which allow using characters from any language, provided there exists a standard web encoding of the characters.

%%ANKI
Basic
What is URI an acronym for?
Back: **U**niform **r**esource **i**dentifier.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359864-->
END%%

%%ANKI
Basic
*Why* is a URI named the way it is?
Back: It is a globally unique identifier for some resource.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359866-->
END%%

%%ANKI
Basic
What is IRI an acronym for?
Back: **I**nternationalized **r**esource **i**dentifier.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359867-->
END%%

%%ANKI
Basic
In what way does an IRI generalize URIs?
Back: It allows any characters with standard web encodings to be used in the identifier.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359871-->
END%%

%%ANKI
Basic
Which of URIs or IRIs are more general?
Back: IRIs.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359873-->
END%%

### URLs

A **uniform resource locator** (URL) is a URI that specifies the means of finding the represented resource. The most commonly used schemes are `http` and `https`.

%%ANKI
Basic
What is URL an acronym for?
Back: **U**niform **r**esource **l**ocator.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359858-->
END%%

%%ANKI
Basic
*Why* is a URL named the way it is?
Back: Its structure specifies how to find the corresponding resource.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359861-->
END%%

%%ANKI
Basic
How do you find the resource represented by a URI?
Back: N/A. This isn't generally possible.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359863-->
END%%

%%ANKI
Basic
In what way does a URI generalize URLs?
Back: A URI does not necessarily specify how to find the represented resource.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359869-->
END%%

%%ANKI
Basic
Which of URIs or URLs are more general?
Back: URIs.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359872-->
END%%

%%ANKI
Basic
Which of IRIs or URLs are more general?
Back: IRIs.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359874-->
END%%

%%ANKI
Basic
What scheme are URLs required to use?
Back: N/A. There exist many possible schemes.
Reference: “Uniform Resource Locator.” In _Wikipedia_, June 20, 2024. [https://en.wikipedia.org/w/index.php?title=URL](https://en.wikipedia.org/w/index.php?title=URL&oldid=1230124093).
<!--ID: 1722193197739-->
END%%

%%ANKI
Basic
What are the two most commonly used URL schemes?
Back: `http` and `https`.
Reference: “Uniform Resource Locator.” In _Wikipedia_, June 20, 2024. [https://en.wikipedia.org/w/index.php?title=URL](https://en.wikipedia.org/w/index.php?title=URL&oldid=1230124093).
<!--ID: 1722193197746-->
END%%

### URNs

A **uniform resource name** (URN) is a URI that uses the `urn` scheme. It is intended to uniquely identify a resource, even when the resource no longer exists.

%%ANKI
Basic
What is URN an acronym for?
Back: **U**niform **r**esource **n**ame.
Reference: “Uniform Resource Identifier.” In _Wikipedia_, July 22, 2024. [https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier](https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier&oldid=1235957234).
<!--ID: 1722192211078-->
END%%

%%ANKI
Basic
*Why* is a URN named the way it is?
Back: It is used to uniquely identify some resource.
Reference: “Uniform Resource Identifier.” In _Wikipedia_, July 22, 2024. [https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier](https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier&oldid=1235957234).
<!--ID: 1722192211083-->
END%%

%%ANKI
Basic
Which of URLs or URNs are more general?
Back: N/A.
Reference: “Uniform Resource Identifier.” In _Wikipedia_, July 22, 2024. [https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier](https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier&oldid=1235957234).
<!--ID: 1722192211087-->
END%%

%%ANKI
Basic
Which of URNs or URIs are more general?
Back: URIs.
Reference: “Uniform Resource Identifier.” In _Wikipedia_, July 22, 2024. [https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier](https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier&oldid=1235957234).
<!--ID: 1722192211089-->
END%%

%%ANKI
Basic
*Why* aren't URLs a subset of URNs?
Back: What a URL represents may change over time.
Reference: “Uniform Resource Identifier.” In _Wikipedia_, July 22, 2024. [https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier](https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier&oldid=1235957234).
<!--ID: 1722192211091-->
END%%

%%ANKI
Basic
*Why* aren't URNs a subset of URLs?
Back: Their structure may not necessarily indicate how to find the resource.
Reference: “Uniform Resource Identifier.” In _Wikipedia_, July 22, 2024. [https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier](https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier&oldid=1235957234).
<!--ID: 1722192211093-->
END%%

%%ANKI
Basic
What scheme are URNs required to use?
Back: `urn`
Reference: “Uniform Resource Name.” In _Wikipedia_, April 26, 2024. [https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Name](https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Name&oldid=1220954593).
<!--ID: 1722193197751-->
END%%

## CURIEs

A **compact URI** (CURIE) is a denser representation of URIs. In its simplest form, it consists of a namespace and identifier separated by a colon. For example, `geo:England`.

%%ANKI
Basic
URIs in RDF are usually represented in what condensed format?
Back: CURIE.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359875-->
END%%

%%ANKI
Basic
What is CURIE an acronym for?
Back: **C**ompact **URI**&.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359876-->
END%%

%%ANKI
Basic
Consider CURIE `geo:England`. What is `geo` an example of?
Back: A namespace.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359877-->
END%%

%%ANKI
Basic
Consider CURIE `geo:England`. What is `England` an example of?
Back: An identifier.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359878-->
END%%

%%ANKI
Basic
In its simplest form, a CURIE is made up of what two parts?
Back: A namespace and an identifier.
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359880-->
END%%

%%ANKI
Basic
The namespace and identifier of a CURIE is usually separated by what?
Back: A colon (`:`).
Reference: Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
<!--ID: 1722191359881-->
END%%

## Bibliography

* Allemang, Dean, James A. Hendler, and Fabien L. Gandon. _Semantic Web for the Working Ontologist_. 3e ed. ACM Books 33. New York: Association for computing machinery, 2020.
* “Uniform Resource Identifier.” In _Wikipedia_, July 22, 2024. [https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier](https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Identifier&oldid=1235957234).
* “Uniform Resource Locator.” In _Wikipedia_, June 20, 2024. [https://en.wikipedia.org/w/index.php?title=URL](https://en.wikipedia.org/w/index.php?title=URL&oldid=1230124093).
* “Uniform Resource Name.” In _Wikipedia_, April 26, 2024. [https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Name](https://en.wikipedia.org/w/index.php?title=Uniform_Resource_Name&oldid=1220954593).