Multiplicity to denote (persistent) Instances?

[Paolo F Cantoni]

As many will know I've been discussing the notion of Instance vs Classifier in (relatively) recent times (see What is an "Instance"?).
As mentioned, UML Objects only relate to run-time instances of UML Classes and thus unsuitable for the modelling of more persistent instances.

I'm, personally, comfortable with the analysis that ArchiMate based models are primarily composed of (persistent) Instances.  As I mentioned, I believe the two sub-types of such instances are "specific" and "placeholder" (rather than "generic" as mentioned in the ArchiMate specification).  So, other than by use of the name (I suggested using the indefinite article - a or an - for placeholder instances), how can we easily differentiate between the two?

The answer is easy and elegant!  The t_object table has a column "Multiplicity" (But see Fix Multiplicity and Cardinality, once and for all!)

[Multiplicity refers to the potential range of set membership and thus is expressed as a range 0..*, 2..4, 1..1 (reduced to 1).  Cardinality refers to the actual number of items in a specific set.  For example, a motor vehicle may have a multiplicity of 1..20 wheels.  This (specific) vehicle has a cardinality of 6 wheels.]

Anyway, it seems to me that by setting the value of the Multiplicity to 1 (1..1) is an apposite mechanism for specifying that the item is a specific instance.  Any other value (including null) defines a non-specific or placeholder instance.  The shapescript can react to the value of Multiplicity and adjust the rendering accordingly.  Also, background queries and online scripts can also react thereto.

Thoughts?

Paolo

[qwerty]

To me a 1-multiplicity is a synonym for a singleton. And that I usually stereotype with <<singleton>>. I can't imagine any other multiplicity classification besides that.

q.

[Paolo F Cantoni]

To me a 1-multiplicity is a synonym for a singleton. And that I usually stereotype with <<singleton>>. I can't imagine any other multiplicity classification besides that.

q.

Yes, conceptually they are singletons, but the item already has a stereotype (to denote the metatype).  We have determined that each item will have ONLY one stereotype (denoting the metatype).  Makes life a LOT simpler!

Also singletons are normally rare (and I suspect, like objects, are really denotations for runtime items) but persistent specific instances aren't.

Paolo