Ensemble is based on message flow, and a data transformation is a way to convert from one message type to another. DTL (Data Transformation Language) adds a layer to this - it provides a graphical way to do the conversion. This is really helpful because most of the time, people with domain-specific knowledge may not have extensive coding skills. However, you always have the ability to do some coding, so if you need or want to, this is available.
DTL has several components: the data transformation engine, the language itself, and the DTL editor.