+-- | A class for XML representations which are children of other
+-- elements. The foal is to associate a child XML element with its
+-- parent element's database type. This is required to construct the
+-- database analogue of @a@ in the 'FromXmlFk' and 'FromXmlFkTeams'
+-- classes.
+--
+class Child a where
+ -- | The type of our parent object, i.e. to the type to whom our
+ -- foreign key will point.
+ type Parent a :: *
+
+
+-- | Some database types cannot be constructed from the XML type
+-- alone; they must be supplied a foreign key to a parent object
+-- first. Members of this class can be converted from an XML
+-- representation to a database representation in this manner.
+--
+class (Child a, ToDb a) => FromXmlFk a where
+ -- | The function that produces a @Db a@ out of a foreign key and an
+ -- @a@. The parameter order makes it easier to map this function
+ -- over a bunch of things.
+ from_xml_fk :: DefaultKey (Parent a) -> a -> Db a
+
+
+-- | A further refinement of 'FromXmlFk'. These types need not only a
+-- foreign key to a parent in order to make the XML -> DB
+-- conversion, but also two foreign keys to away/home teams (as
+-- represented in "TSN.Team").
+--
+class (Child a, ToDb a) => FromXmlFkTeams a where
+ -- | The function that produces a @Db a@ out of a parent foreign
+ -- key, two team foreign keys, and an @a@. The parameter order makes
+ -- it easier to map this function over a bunch of things.
+ from_xml_fk_teams :: DefaultKey (Parent a)
+ -> DefaultKey Team -- ^ The away team FK
+ -> DefaultKey Team -- ^ The home team FK
+ -> a
+ -> Db a
+
+