Partitive

Partitive case is a instance of inherent case. Partitive case is optionally assigned by unaccusative verbs, such as Italian arrivare, to a post-verbal subject, which is in fact the internal argument:

(i) E' arrivato Gianni is arrived Gianni 'Gianni arrived'

According to Belletti (1988), partitive case can be assigned if no case (Nominative or Accusative) is assigned otherwise.

Links
Utrecht Lexicon of Linguistics