-To relate the two, a third table may exist with name <parent
-table>__<child table>. Note the two underscores. This prevents
-ambiguity when the child table itself contains underscores. The table
-joining \(dqnews\(dq with \(dqnews_locations\(dq is thus called
-\(dqnews__news_locations\(dq.
+To relate the two, a third table may exist with name
+<parent>__<child>. Note the two underscores. This prevents ambiguity
+when the child table itself contains underscores. The table joining
+\(dqnews\(dq with \(dqnews_locations\(dq is thus called
+\(dqnews__news_locations\(dq. This is necessary when the child table
+has a unique constraint; we don't want to blindly insert duplicate
+records keyed to the parent. Instead we'd like to use the third table
+to map an existing child to the new parent.