Function strings for functions can be automatically generated for function-string classes that come with Replication Server.
Function strings must be customized for any function-string class that the user creates that does not inherit its functions strings from one of the provided classes. To customize a function string, you modify an existing function string with data-server-specific commands or by invoking a remote procedure call (RPC). A customized function string can also contain function string variables that represent the values of columns, procedure parameters, system-defined information, and user-defined variables. Replication Server replaces the variables with actual values before sending function strings to the data server.
See Replication Server Administration Guide Volume 2 > Customize Database Operations for details.