+ game_id :: Maybe Int, -- ^ These are optional because they are missing
+ -- from at least the MLB_Matchup_XML.dtd documents.
+ -- They provide foreign keys into any tables storing
+ -- games with their IDs.
+
+ schedule_id :: Maybe Int, -- ^ Optional key into any table storing a
+ -- schedule along with its ID. We've noticed
+ -- them missing in e.g. recapxml.dtd documents.