What scope(s) is "hasMany" a part of?
In any case, when one thing hasMany of another how/where does it show up in application and database logic?

The only way I can think to answer this question is with another example of hasMany that may or may not answer your question.

err, except I should have called the table &quot;comment&quot; but I think the point stands.
I don't know that this really helps you understand anymore than what you already had.
So I'll also share a query that might demonstrate how this works:
declare @var char(5)
set @var = 'query'

select
   c.id
  ,c.text
  ,c.author
from comment c
inner join post p
   on p.id = c.parentid

which we expect to return many rows, because one post generally has many comments (in theory, of course not all posts will have comments)

Update:
So here's the thing about relations: They are EASY to model via diagram (see the very first tool I pulled out to answer this question) but they are HARD to diagram via text. So instead of trying to define whether we mean 1:M or 0:N, we just write it in &quot;near English&quot; and say what we intend. Here's some alternatives:
one to one           hasOne               post hasOne author (not true for CW ;])
one to many          hasMany              The one in question
many to one          belongsTo            parent child, comments belongTo post
many to many         hasAndBelongsToMany  This describes a complex relationship
many to many to many hasManyAndBelongsToMany

As you see they can get quite complicated. This would ... once again! ... indicate a need to refactor your business logic into simpler and smaller chunks.
These can also be called &quot;association types&quot; and may be indicated by verbage like &quot;WrittenBy&quot; (a many to one) or &quot;IsOwnedBy&quot; (one to one? - context is key)
Before I walk away from the &quot;hasMany&quot; concept for the last time (well this is an update, more will likely be written) I want to mention that while it's useful for &quot;plain English descriptions&quot;, it's also used in ActiveRecord styled installations. Take, for instance, Ruby. http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html The rest of this post (so far) is taken from that page:
class Project &lt; ActiveRecord::Base
  belongs_to              :portfolio
  has_one                 :project_manager
  has_many                :milestones
  has_and_belongs_to_many :categories
end

This allows the ActiveRecord ORM to create the data model and to maintain the relationships as specified by the business logic within the program. But I don't write Ruby or Rails so that's as far as I can tell you, I just know that it exists there.