SYSML17 — Resolve inconsistency concerning restricion of ItemFlow type hierarchy

Issue:
The descriptions in the specification are inconsistent regarding the constraints of what can actually flow over a connector.
The ItemFlow is used to constrain what actually flows w/r/t the flow properties which specify what can flow.
In other sections the specifications suggest that the ItemFlow actually loosening the constraint by allowing more general types to be flowing.

Description:
These are the inconsistent parts in the specification:

9.3.2.11 ItemFlow, p86 states:
An ItemFlow describes the flow of items across a connector or an association. It may constrain the item exchange between blocks, block usages, or ports as specified by their flow properties.

9.3.2.11 ItemFlow, p87 states:
Each classifier of conveyed items on an item flow must be the same as, a specialization of, or a generalization of at least one flow property type on each end of the connected block usages.

9.4.6 Item Flow Decomposition, p95
Item flows can also be more general than the actual flow, as shown by the connector on the right. The water distiller produces distilled water, but the item flow is for any kind of fluid. The connection to the water heater is
compatible because it accepts any kind of water, including distilled. The item flow does not require the heater to accept any kind of fluid, because the source of flow is still producing water, regardless of the generality of the item flow.

Figure 9.15, p95 - Usage example of item flows in internal block diagrams
Item Flow is Fluid.

Defer

Issue deferred