Extension versus Specialization

[Pascal Huau]

Dear Express experts,


I would liket to get your recommendation for a particular case of use of Express2

Example:
 

TYPE identification_item = EXTENSIBLE SELECT;

END_TYPE;

TYPE alias_identification_item = EXTENSIBLE SELECT BASED ON identification_item;
END_TYPE; 


ENTITY Alias_identification
  SUBTYPE OF (Identification_assignment) ; 
  SELF\Identification_assignment.items : SET [1:?] OF alias_identification_item;

END_ENTITY;



ENTITY Identification_assignment;

  identifier : STRING;

  role : OPTIONAL STRING;

  description : OPTIONAL STRING;

  items : SET [1:?] OF identification_item;

END_ENTITY;



My understanding is that the specification of alias_identification_item involves that:

-  all entiy types contained in identification_item are allowed to get an alias.

- all entity types contained in alias_identification_item are allowed to get an identification assigned



As it may not be suitable that the list of entities that may get an alias, be a superset of the list of entities that may get an identification, how to specify the entity alias_identification if alias_identification_item is no more an extension of identification_item? Can alias_identification stay a subtype of Identification_assignment? (my opinion is No, but I would like a confirmation from the best experts)



Regards,

Pascal Huau
Association GOSET
107,111 avenue Georges Clemenceau
92000 Nanterre
FRANCE

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