modifiers - Explanation on when the possessive should be used instead of an attributive noun

How would you explain to a person who is learning English, and whose native language does not have attributive nouns, when the possessive should be used instead of an attributive noun?

In particular, how would you explain it referring to the following list of sentences?

• Today's news is bad


• This week's schedule has been changed


• Tomorrow's lunch will be at the French restaurant


• This year's report will be communicated in the reunion room


• Last summer's vacations were memorable


• Last year's meetings were a complete disaster

Answer

All of your examples have something in common: though some of the attributives that you give have the form of noun phrases, they are all primarily adverbial in usage:

• Today we're watching the news.


• This week we have to make a schedule.


• Tomorrow we should have lunch.


• This year they gave a good report.


• We visited there last summer.


• She had the records of the meetings last year.

These adverbial phrases have limited currency as nouns. You can sometimes use them as the objects of prepositions, as in Before yesterday I had never heard of her, or as the subject of a sentence as in Today was a good day. However, they don't show the full range of syntactic variation that ordinary noun phrases do: they can't be pluralized and they resist being used as attributives. As your examples show, if you want to use an adverbial in this manner, you're required to mark it with the possessive -'s.