The pg95 module has functions for interpreting tuples and rows of tables as objects in the RScheme object system. This is done by making use of PostgresQL type introspection techniques and RScheme class introspection.
The general rule is that as long as the the name of the class slots are the same as the names of the tuple fields, then the mapper can fill in the appropriate slots. The slot with name oid can be used to refer to the PostgresQL object id.