Before you can work with a data table or with objects in a data table, you must first open the data table and assign a reference to it. In this book, dt represents a reference to a data table object.
To manipulate an object in JSL, you send a message to the reference that represents the object, asking the object to perform one of its tasks. Messages are commands that can be understood only in context by a particular type of object. For example, messages for data table objects include Save, New Column, Sort, and so on. Most of these messages would not make sense for another object, such as a platform object.