Michael Hong wrote:

> So in this case, we can have the objects be a set of numbers [...?]

In the category \$$\mathbf{Set}\$$, the objects are sets! That's unarguable. To go further, you need to make some decisions about what you mean by "set". That's what [set theory](https://en.wikipedia.org/wiki/Set_theory) is all about. It's a big subject, with many different approaches. But almost any approach to set theory is willing to accept a set of numbers as an example of a set.

A set of _people_ is a bit trickier, because a person is (most likely) not a mathematical entity. But as I said before, computers encode everything in terms of mathematical entities, so in work on databases we don't actually need to deal with sets of people, just sets whose elements correspond to people in some way.