MS SQL Server allows you to define your own data types that map to native MS SQL Server data types. When the DataServer reads the schema information for a user-defined data type, it reads the MS SQL Server base data type and maps it to the equivalent OpenEdge data type. Suppose, for example, that you create a data type named phone_number and map it to the char data type. In the schema holder, the DataServer represents your phone_number data type as a CHARACTER data type. If you make any changes to a user-defined data type, you must update the schema holder to reflect those changes.