You can create an identifier from the property sheet of a class or interface.
            - 
                    Open the Identifiers tab in the property sheet of a class or interface, and click the Add a Row tool. 
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                    Open the Attributes tab in the property sheet of a class or interface, and select the Primary Identifier checkbox when you create an attribute. 
 
For general information about creating objects, see Core Features Guide > Modeling with PowerDesigner > Objects.