Grokking the word `scheme` in URI

Question

A generic form of URI is:

scheme:[//[user[:password]@]host[:port]][/path][?query][#fragment]

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

in Oxford:scheme | Definition of scheme in English by Oxford Dictionries

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?

Answer 1

It's Oxford's definition 2: An ordered system or arrangement.

FTP and HTTP, for example, are ordered systems for accessing data. The URI developed from the URL, which was originally designed to encompass these and a couple other systems for accessing the internet.

People who write standards would rather keep things consistent than make every word used fit its use in day-to-day speech, so when URI's to refer to local files or triggering actions like launching an email program were added, they might rather keep using the word scheme than change it.