What is the correct way to name 'storage of documents' with usage of 'repository' and 'document' words?
Which one is correct:
- document repository
- documents repository
In English, many expressions that can be expressed in the form "a SINGULARX of PLURALY" can also be expressed in the apparent form "a SINGULARY SINGULARX." That statement is almost incoherent as written, but what I mean is that you can convert many phrases that refer to a singular thing composed of multiple other things in ways that consistently shift the seeming plurality of the second element. For example, the following expressions are more or less equivalent:
a hive of bees = a bee hive
a collection of stamps = a stamp collection
a field of oats = an oat field
a herd of elephants = an elephant herd
a bouquet of flowers = a flower bouquet
a pack of cigarettes = a cigarette pack
a flock of starlings = a starling flock
a file of receipts = a receipt file
In each case, when we change the plural noun at the end of the prepositional phrase into a modifier before the singular noun, the modifier loses the s that it had as a plural noun.
There are a number of exceptions to this rule, but "document repository" (= "repository of documents") is not one of them. As Dan Bron notes in a comment above, the Ngram chart for "document repository" (blue line) versus "documents repository" (red line) for the period 1950–2000 clearly indicates the large advantage in usage that "document repository" holds over "documents repository" in the Google Books database, especially since the early 1990s:
That doesn't mean that no one writing in English uses "documents repository"—clearly some people do. But just as clearly, the preponderance of usage favors "document repository."