A key-value store would be a store of one thing: key values. A hyphen combines two words to make an adjective, which describes the word that follows:
A used-car lot
A value-added tax
A key-based access system
An on/off switch
A win/win situation
A master/slave arrangement
All of your slash examples represent either–or situations. A swich turns it on or off, the situation is a win in the first outcome or a win in the second outcome, etc.
It's true that key–value store shouldn't be written with a hyphen. It should be written with an en dash, which is used "to contrast values or illustrate a relationship between two things [... e.g.] Mother–daughter relationship"
https://en.wikipedia.org/wiki/Dash#En_dash
I just didn't want to bother with typography at that level of pedanticism.
No, they don't. A master/slave configuration (of hard drives, for example) involves two things. I specifically included it to head off the exact objection you're raising.
"...the slash is now used to represent division and fractions, as a date separator, in between multiple alternative or related terms"
-Wikipedia
And what is a key/value store? A store of related terms.
And if you had a system that only allowed a finite collection of key values, where might you put them? A key-value store.
The hard drives are either master or slave. A hard drive is not a master-and-slave.
Exactly. And an entry in a key/value store is either a key or a value. Not both.
No, an entry is a key-and-value pair. Are you deriously suggesting it is possible to add only keys without corresponding values, or vice versa?