How to refer to multiple entities that belong to multiple entities correctly?

Question

So, for example, there are multiple books by multiple authors, and I want to talk about them. Is it correct to write "books authors"? Because "book authors" sounds like authors of one book...

I saw another example like this "The list contains English and French country names as well as the local names of the countries". I see countries are singular in the first case but plural in the second.

My use case is making identifiers in programming (variable and database table(s?) names), and I have not seen much use of "of" there. Maybe I should introduce "of" nevertheless.

Answer 1

variable and database table(s?) names

We are clear on the fact that names should be in the plural. As for table(s) I think it should be singular before names (database table names) but plural if you choose to say names OF tables (this second phrasing is not idiomatic).

In database table names, "table" is an attributive noun which should normally be in the singular. On the site of the American Journal Experts I found this explanation which backs up what I have just said:

Two common pet peeves among language editors relate to incorrect noun pluralization, most often meaning that “s” or “es” is unnecessarily added to the end of a noun. The first type of error is unnecessary pluralization of a noun used as an adjective, also known as an attributive noun. For example,

• Nanoparticle structures (correct)
• Nanoparticles structures (incorrect)
• Five-week-old mice (correct)
• Five-weeks-old mice (incorrect)

Generally, an attributive noun should not be plural, even if the noun that is being modified (“structures” and “mice” in the examples above) is plural; exceptions to this rule (e.g., “sports games”) are infrequent.

Now, while searching for the phrasing you are giving I found this article on the teamten.com site, whose title is

Use singular nouns for database table names

The first sentence of the article has the other way of phrasing:

A common debate in relational database circles is whether the names of tables should be singular or plural.

If you look up these phrases on Gngram you will find that database table names is the one commonly used:

Note that

1. names of database tables is almost not used.
2. There is no instance of database tables names.

Answer 2

Is it correct to write "books authors"? Because "book authors" sounds like authors of one book.

1. No it is not correct to write "books authors"

2. "book authors" sounds like authors of one book - It doesn't sound that way to a native English speaker.

A book may be written by several authors and an author may write several books. The phrase 10 book authors, tells you that there are ten humans who are authors. It does not tell you which authors wrote which books. It does not tell you how many books. There may be one book written by all the authors or a thousand books written by any combination of authors.

Conclusion

"book authors" only tells you that that are numerous authors, it says nothing about how many books they have written. You can think of "book" as acting as an adjective.**

We can talk about 10 electric guitars but not 10 electrics guitars. There is no agreement of adjectives in English.

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** As pointed out by fev, a noun used as an adjective can be called an epithet noun.