Forward and reverse data type mappings
Forward type mappings and reverse type mappings are the two kinds of mappings between data source data types and federated database data types.
A forward type mapping is a mapping from a remote data type to a comparable local data type. Forward type mappings are used when you a create a nickname for a data source object. The comparable local type for each column in the data source object is stored in the global catalog.
A reverse type mapping is a mapping from a local data type to a comparable remote data type. Reverse type mapping is used with transparent DDL.
Figure 1 shows forward and reverse data type mapping.
