Quine wrote that one's ontology coincides with the ranges of the variables in one's formalism. This usage is entirely appropriate for AI. Present philosophers, Quine perhaps included, are often too stingy in the reifications they permit. It is sometimes necessary to quantify over beliefs, hopes and goals.
When programs interact with people or other programs they often perform speech acts in the sense studied by Austin and Searle. Quantification over promises, obligations, questions, answers to questions, offers, acceptances and declinations are required.