A model of the DTD (Document Type Definition) type describes the rules according to which an XML document of a specific type must be structured. The description is provided in the form of element type declarations.

For example, you can use a DTD to define the general structure of a document type. A valid document of a document type defined in the DTD is an XML document. This has the advantage that the document can be processed by various programs based on the corresponding DTD.

Starting from an Element type object, the model must be set up according to a strict hierarchy. The source object must not have any incoming connections. Furthermore, connections must always run from the superior object to the subordinate object. While you can describe all element types in a DTD model for clear document structures, with complex structures you have the option to declare an element type in an assigned DTD model.

If you work with assignments, the assigned model must contain the complete description of the element type.