Flat database rows are easy to store, but they are awkward to render when the UI wants a nested menu, category tree, org chart, or threaded comment list. Most hierarchical data is stored with a simple relationship: Each row has its own `id` Each row may have a `parentID` Rows with no parent are top-level items Rows with a parent belong under another row That storage model works well in SQL. It keeps the table simple and avoids nesting data inside the database. But once those