A customizer provides out-of-the-box message types based on the messaging standard. You select a message type and customize the message structure by adding, editing, and removing elements. You can save the message to continue editing it later, or you can publish the message as a data service so you can use it in a Data Services transformation. You can't edit the published data service, but you can edit the customizer and republish the message as another data service using a different name.