A generic form of URI is:
scheme here means protocol which whereas has no relation to its original definition. I cannot really understand it intuitively.
In wikipedia Uniform Resource Identifier - Wikipedia
Examples of popular schemes include http(s), ftp, mailto, file, data, and irc. URI schemes should be registered with the Internet Assigned Numbers Authority (IANA), although non-registered schemes are used in practice.[b]
I can understand it's meaning. I cannot interpret it usage why 'scheme' is used instead of 'protocol'.
Scheme in MW dictionary: Scheme | Definition of Scheme by Merriam-Webster
1.a concise statement or table
2.a plan or program of action;
3.a systematic or organized configuration
1.A secret or underhand plan; a plot.
2.A particular ordered system or arrangement.
It seems 'A particular ordered system or arrangement' make sense.
If it does, an ordered system or arrangement should comprise the completed URI. 'scheme:[//[user[:password]@]host[:port]][/path][?query][#fragment]' should be renamed as 'scheme' not URI.
So, what's the original meaning of the word to which 'scheme' here relate?