the Confusing URI, URL and URN

  Naming and Addressing are two key issues that every large scale distributed system should face. (they are also known as persistence/availability)

  URI emphasizes on both sides of them, while URL emphasizes on location and URN emphasizes on naming. So we can say that the URN defines an item's identity, while the URL provides a method for finding it.

  But we can't say that URI consists of two classes of identifiers: URL and URN. According to w3c's formal documentation, URL is a useful but informal concept: a URL is a type of URI that identifies a resource via a representation of its primary access mechanism (e.g., its network "location"), rather than by some other attributes it may have. While URN is now just an URI scheme, which itself will contain some subspaces, for example: urn:issn:1535-3613


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