Backgrounds sourceentry conversion

schema/backgrounds.sql

@@ -4,9 +4,17 @@ CREATE TABLE backgrounds (
   bg_id INTEGER PRIMARY KEY,
   "name" TEXT NOT NULL UNIQUE,
   descr TEXT NOT NULL,
-  sources_id INTEGER NOT NULL,
-  sources_pages TEXT NOT NULL,
   is_comty_use BOOLEAN NOT NULL, -- false = no community use policy required
   is_specific_to_adv BOOLEAN NOT NULL, -- means the background is specific to its adventure
   FOREIGN KEY (sources_id) REFERENCES sources(sources_id)
 );
+
+-- Joining table --
+CREATE TABLE backgrounds_sourceentries (
+	 id INTEGER PRIMARY KEY
+  ,bg_id INTEGER NOT NULL
+  ,sourceentry_id INTEGER NOT NULL
+  ,UNIQUE (id, bg_id, soruceentry_id),
+  ,FOREIGN KEY (bg_id) REFERENCES backgrounds(bg_id)
+  ,FOREIGN KEY (sourceentry_id) REFERENCES sourceentries(sourceentry_id)
+);