location transperency:
In computer networks location transparency describes names used to identify network resources independent of both the user's location and the resource location.
A distributed system will need to employ a networked scheme for naming resources.
In other words it is an idea that the resources can be accessed by a user from anywhere on the network without knowing where the resource is located. A file could be on the user's own PC, or thousands of miles away on other servers.
url:
Uniform Resource Locator is a compact string of characters used to represent a resource available on the Internet.[1] In popular usage and many technical documents, it is a synonym for Uniform Resource Identifier (URI).
uri:
a Uniform Resource Identifier (URI) is a compact string of characters used to identify or name a resource on the Internet. The main purpose of this identification is to enable interaction with representations of the resource over a network, typically the World Wide Web, using specific protocols. URIs are defined in schemes defining a specific syntax and associated protocols.
urn:
A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) that uses the urn scheme, and does not imply availability of the identified resource. Both URNs (names) and URLs (locators) are URIs, and a particular URI may be a name and a locator at the same time.