Multiplicity in ports

[Ignacio G. T.]

I am a little confounded by the relationship between multiplicity in ports and multiplicity in connectors, inside a composite structure diagram.

Let's suppose we have a device like this:



And its composite structure diagram:



So far, so good. Now, suppose I want to take advantage form the fact that ports pact1 and pact2 are of the same type; ditto for pcpu1, pcpu2. I think I can model itlike this:



And the composite structure diagram:



Now, how can I be sure that the latter  diagram means the same as the first composite structure diagram, and not this one?:



Or is this not equivalent because of some restrictions derived from the multiplicity (1) of the end associations?

In other words, I think I know how multiplicity works with associations between classes (and parts) without ports, but I am not sure how it works with ports. Can someone point to the correct rules?

I've seen complicated examples in Internal Block Diagrams (A Practical Guide to SysML, by Friedenthal and others) that I don't fully understand, because no clear (to me) rule is formulated.

The above examples are the simplest ones I cannot fully elucidate. I have more complicated examples for the adventurer who dares to offer me a good response.  

[Helmut Ortmann]

Hello,

in my opinion a port has no multiplicity, or just 1, because it's embedded (or just included) in an element. Therefore the port has the multiplicity of 1.

If a class has a port every instance of this class has this port. If a part has a port every instance of this part has exactly one port.

Kind regards,

Helmut

[qwerty]

I guess Helmut is right. Imagine a port as electrically wired set of pins. Now if you have such a double-port and they share the same pins the they are the same - actually one port. If you have the 2nd as some kind of backup it will have a different cabling so it's use as backup is guaranteed. In that case you have two different ports. In short: a multiplicity does not make sense. I have no idea whether UML or SysML designers have thought of this an blocked multiplicity (or forgot to block it).

q.

[Eve]

A port is a type of Property. It adds a couple of attributes and associations and specifies that the composition type must be composite. I don't see any reason why it can't have a multiplicity.