In Japanese, it's very common to refer back to a noun without saying the noun itself again. This is done by using the particle の, functioning in a similar manner to its use for indicating possession. The noun that would typically come after の is omitted, as it has either been stated previously or is clear from the situation.

• このカメラはマリアさんのです。
  This camera is Maria's (camera).
• その鞄(かばん)は誰(だれ)の？先生(せんせい)の？
  That bag, whose (bag) is it? Is it the teacher's (bag)?

In the sentences above, it would still be grammatically sound to include the noun after の, but as the English translations show, this creates unnecessary repetition. This practice is known as word stacking (重(かさ)ね言葉(ことば)) in Japanese and is generally avoided in good conversation and writing. Nevertheless, it's helpful to remember that this の is fundamentally the same as the possessive の (the following word is simply implied).

• その絵(え)、有名(ゆうめい)な画家(がか)が描(か)いたのですか。
  That painting, is it one that a famous artist drew?

From this example, it's evident that repeating the noun is superfluous. The Japanese language often favors conciseness by not restating words when the context is clear. This particular example illustrates noun replacement, which is distinct from the noun omission shown earlier, and is another common function of の that will be explored in a future lesson.