The relationship between part and reference Properties and Associations is something that can cause a fair bit of confusion with SysML beginners.
A part Property need not have an Association, that is, it is not necessarily a 'memberEnd' of any Association, in which case it won't have a 'Property::association' populated.
The image compares a part Property local:Part
that does not have an 'association' with a part Property end:Part
that does, being a 'memberEnd' of a uni-directional Association.
See the named aOwned:Assembly
Property at the non-navigable end of Association UniDirectional
(which Property is owned by that Association)? You don't often have to name such properties in typical SysML modelling, as you can't "naturally" navigate (in the model) to it from the Part
block anyway (although in the tool itself one can).
The case of a reference Property ref:NotPart
as one 'memberEnd' of a bi-directional Association is also shown. There are many other possible permutations and combinations. Some more cases are explore here:
Managing part and reference Properties vs Associations in MagicDraw/Cameo
By default, Associations are NOT created when a part Property is created, although you can change that under the Project Settings
If you drag a part out of a Block symbol's parts compartment, a uni-directional Association will be created, or if one already exists it will be displayed (instead of creating a new one).
Visit also: