SysMLv1: A part Property or reference Property is not necessarily a 'memberEnd' or 'ownedEnd' of an Association ('association' or 'owningAssociation'). But an Association always as at least 2 'memberEnd' Properties. (With some MagicDraw/Cameo tool tips.)

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).

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