Return the primary implementation type for this access method.
Although an access method may implement more than one implementation
type, this is the expected one. The access manager will put the
primary implementation type in a hash table for fast access.
Return the primary format that this access method supports.
Although an access method may support more than one format, this
is the usual one. the access manager will put the primary format
in a hash table for fast access to the appropriate method.