Is there an empty URI?

问题:

I working on a routine that parses a URI. Among obvious cases there is an empty string case. Is the empty string a valid input? What would be an outcome URI of an empty string?

回答1:

An empty string can’t possibly be a URI. The general URI syntax specifies that at least the scheme component followed by a : followed by the hier-part component (which may be empty) must be present.

But a relative URI reference can be empty. The syntax of relative references specifies that at least the relative-part component must be present, but it’s allowed to be empty (path-empty).

An empty relative URI reference is a same-document reference (bold emphasis mine):

The most frequent examples of same-document references are relative references that are empty or include only the number sign ("#") separator followed by a fragment identifier.

回答2:

Since the root of a URI is a limited set we know it does not have a valid root. It therefore does not identify anything and is invalid as an identifier. But this might have a meaning in your context still since tere is no specific standard for a URI.