clarification question: new SDO vs SCO types

Hi again,

I have one more clarification question that I am hoping someone can 
answer. In the specification there doesn't seem to be any property that 
distinguishes SDOs from SCOs, other than the "type" property (meaning, 
you have to know the type hierarchy to know that "location" is an SDO 
but "email-message" is an SCO).

How, then, does an implementer know if a newly defined type, provided by 
the extension mechanism, is an SDO or SCO? The answer may possible be: 
they don't.

While I can't see a big problem with not knowing this information for a 
particular object, I can see two minor possible problems: (1) the 
"consists-of" relationship can take as a a target "all STIX CSOs", so if 
you don't know which newly defined objects are CSOs you don't know which 
types are valid in this position. I may have missed analogous cases 
elsewhere in the specification. And, (2), there are semantic differences 
between the two classes and so implementations may wish to handle SDOs 
vs SCOs differently, and so not knowing if a newly defined type is one 
or the other would make different behaviors for SDOs for SCOs problematic.

Any insight you can give into this matter would be much appreciated. Best,

Mark

_______________________
Mark A. Finlayson, Ph.D.
Eminent Scholar Chaired Associate Professor, FIU KFSCIS, Cognac Lab
Interim Associate Director, FIU KFSCIS
Edison Fellow for AI, USPTO
11200 SW 8th Street, CASE Room 362, Miami, FL 33199
+1.305.348.7988 (office); +1.617.515.0708 (mobile); 
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