Attributes, Associations and Operations cannot simultaneously be abstract and class.
The ‘class’ status of an Attribute, Association, or Operation makes them static, meaning only one instance can exist at any given time.
The ‘a_bstract_’ status, by definition, stipulates that an element cannot be instantiated. The two properties are therefore incompatible and cannot both be true at the same time.
Choose between these two statuses, and set only one of them to true.