The difference between them is straightforward after knowing their definitions:
Uniform Resource Identifier (URI) − a sequence of characters that allows the complete identification of any abstract or physical resource
Uniform Resource Locator (URL) − a subset of URI that, in addition to identifying where a resource is available, describes the primary mechanism to access it
Every URI, regardless if it’s a URL or not, follows a particular form:
scheme:[//authority][/path][?query][#fragment]
Where each part is described as follows:
*scheme* − for URLs, is the name of the protocol used to access the resource, for other URIs, is a name that refers to a specification for assigning identifiers within that scheme
authority − an optional part comprised of user authentication information, a host and an optional port
*path* − it serves to identify a resource within the scope of its scheme and authority
*query* − additional data that, along with the path, serves to identify a resource. For URLs, this is the query string
*fragment* − an optional identifier to a specific part of the resource
To easily identify if a particular URI is also a URL, we can check its scheme. Every URL has to start with any of these schemes: ftp, http, https,gopher, mailto, news, nntp, telnet, wais, file, or prospero. If it doesn’t start with it, then it’s not a URL.
