If you do not want to use the content generator to generate a data model automatically, you can create a Public Solution (PS) data model from scratch using the design time in the ABAP Workbench. You might prefer to create a data model manually, for example, if you want to write your own code or if you want to use existing ABAP Dictionary (DDIC) structures. When you create your own data model, you build the entire structure from scratch.
If you choose to create your own data model, you have the advantage that you can edit the data model's object structure and change the properties of any of its entities; whereas you can only can add or delete external relations for PS data models that the content generator has generated automatically. Use the Properties Editor to define and maintain entity properties. If you want to add or edit user-specific annotations, you must create a User Centric (UC) data model and then you use the Annotation Editor to annotate entities such as data objects, properties, relations, and operations.
For more information about creating a data model from scratch using the design time in the ABAP Workbench, select the appropriate SAP Gateway programming paradigm: