the text you quoted doesn't claim anywhere that the word "relational" has to do with relationships between tables
Hmm, I disagree.
This type of structure is called a relational database: we have multiple tables that connect to one another via keys
The emphasis here is on the connections rather than the tables. Why say "multiple tables"?
In writing for beginners the author should just say something truthy like: "A relational database is a database where all data is stored in values of an algebraic data type called a 'relation'. SQL uses the word 'table' instead of 'relation', but the two words mean roughly the same thing."
This is why I used the word "claim". The sentence you quoted can be construed to imply that relational databases are relational because of the relationships between tables, but it certainly does not claim that.
I'm not merely nitpicking here, I'm trying to explain that what you perceive as the author's mistake is, in fact, your interpretation. I do, however, completely agree with you in that the text would have been better if the author phrased it in such a way as to deliberately avoid the possibility of that particular interpretation.
In writing for beginners the author should just say something truthy like: "A relational database is a database where all data is stored in values of an algebraic data type called a 'relation'. SQL uses the word 'table' instead of 'relation', but the two words mean roughly the same thing."
What you've written here is worse, for the simple reason it is now semantically wrong instead of just syntactically wrong in the use of the word relational.
As an example, all relational databases that the average reader can be expected to have heard of use bags(multisets) instead of sets, so they in fact don't store data in relations.
Language gets polluted over time. Trying to force a technically correct but obsolete meaning is not helpful to anyone.
Hmm, I disagree.
This type of structure is called a relational database: we have multiple tables that connect to one another via keys
The emphasis here is on the connections rather than the tables. Why say "multiple tables"?
In writing for beginners the author should just say something truthy like: "A relational database is a database where all data is stored in values of an algebraic data type called a 'relation'. SQL uses the word 'table' instead of 'relation', but the two words mean roughly the same thing."