For clarity, a Notice is eg a Wedding, Birth or Death announcement which appears in a newspaper. This is (an excerpt of) what my DB looks like:

   Table: object (generic object)
   ------------------------------
    id
    type_id
    status
    parent_id
    creator_id
    created
    last_modified

  Table: notice (adds notice specific fields to the object table)
  ---------------------------------------------------------------
    id (1 to 1 relationship with object.id)
    notice_type (ie wedding, funeral, birth etc)
    title
    content
    etc

  Table: charity (adds charity specific fields to the object table)
  -----------------------------------------------------------------
    id (1 to 1 relationship with object.id)
    name
    description
    url
    etc
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The editor of a notice can choose a number of charities to link to, so a notice can have many charities. This is stored in the members table:

   Table: members  (link table)
   ----------------------------
    set_id    (in this example, the notice ID)
    member_id (in this example, the charity ID)
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Notices can have many Comments, Images, Charities, Editors. So my question really boiled down to, should I have

• separate List/Set/Container objects for each list of items, so that you create a new ImageList, which is a child (not a subclass) of the Notice, and the members.set_id == ImageList.id
• or set_id == notice.id, and then you filter the set members you want by object type (ie image/comment etc)

After discussion in the CB with bart and castaway, I think i've abandoned both of those, and now what I'm going to do is the following:

• A Set does not live in the database as an object, neither does Notice inherit from the Set
• Instead, I can create a Set object as follows:

     $set = Set->new({
          set_id      => $notice->id,
          name        => 'imagelist',  # combined with set_id to provide
  + an ID for caching
          selectors   => {
              type       => 'image'
          },
     });
  [download]

  ... which is really just a glorified array, with methods to check membership, and to add / delete members from the list, almost like an SQL view.