SYSML17 — SysML: UML Qualified Associations

SysML currently discards UML 2.1 qualified associations (see 8.3.1.4) as not being of interest to the SE community.

I contest this on two grounds –

1) a. Qualifiers are used expressively and meaningfully to explain domain situations that have nothing to do with data modeling. For example, when I say a baseball roster had 9 members and that there are 9 positions to fill, I am not explicitly saying that there is one person per position. Qualifiers allow me to clarify this piece of the real world and would be very useful on a BDD.

b. Qualifiers are also used idiomatically with generalization discriminators to tie parallel generalization structures together. They are capable of modeling situations, such as when there are many types of missiles, each with their own launcher type.

c. Qualifiers are also used to indicate addressing schemes and mechanisms. For example, by placing an operation/activity etc that returns a type in a qualifier, one can specify the mapping or prioritization /ordering algorithm. Specifying such algorithms may be the SE’s job, when it part of an equation report, algorithm development. This could fit into SysML and support allocation to functional (target prioritization scheme, best antenna-signal function) and structural components (packet routers). This is fully in the spirit of what practicing SEs do and would round out the capability of SysML.[Note that this capability could be delayed for a later SysML, the other parts should be addressed sooner]

2) Qualifiers appear to be part of small part of UML that is incompatible with use with a SysML strict profile mechanism. Imagine a model done in strict SysML, then brought into UML, where a qualifier is added to the relationship, changing the multiplicity at one end. If the model is then brought back into (strict) SysML and the qualifier is then dropped, the multiplicity cannot be automatically restored (or determined from the model). Because of this, qualifiers must be forbidden in UML in such contexts

Closed because a rationale is missing

In principle, it would be possible to introduce qualified associations, since it is part of UML. It was discussed several times in previous issues and we agreed that it should be covered by SysML v2.