区分
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URI&URL
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The main differences are::

	- URI identifies a resource, URL provides a location for the resource.
	- URI includes URLs as well as URNs (Uniform Resource Names). URL only includes web addresses.
	- URL must contain location info like protocol and domain name. URI does not necessarily have that.
	- URL is a concrete resource locator, URI can be an abstract identifier.

Some examples to illustrate the differences::

	- mailto:user@example.com is a URI but not a URL. 
		It identifies an email address but does not specify the location.
	- ISBN:978-0-306-40615-7 is a URI but not a URL. 
		It identifies a book but does not tell you where to find it.
	- https://www.example.com/users/1 is both a URI and a URL. 
		It identifies resource with ID 1 and also specifies the location (the domain and path).