Transformations can be used to change the design. For instance while Engineering to Relational you could add columns to a table. Usually those columns are of a type of technical columns (for example creator, created, modifier, modified), or columns that should always exist for a type of table based on the methodology used (for example Data Vault defines certain columns to exist for certain kinds of tables: hubs, links and satellites). Or you can use them anywhere in your design to automate changes. To execute a script right-click on the Browser and select Apply Custom Transformation Scripts:
Select the script/scripts from the list and press Apply:
In short: Transformations are used to change the design programmatically.
Table DDL Transformations
Table DDL Transformations can be used to change the DDL Data Modeler generates. The design itself is not changed, only the DDL script. This can be used for example to generate the journaling mechanism (journaling tables and triggers) or DDL scripts for a RDBMS that is not supported by Data Modeler, for instance MySQL.
To use a script defined select it from the list in DDL Generation:
Define the tables that DDL generation you want to be affected by the script:
And Generate the DDL by pressing OK.
In short: Table DDL Transformations are used to change the DDL generated.