BACM11 — Sequencing of ValueStreamStages

ValueStreamStages are commonly ordered in display.
There is a question about whether this implies an operational ordering that disallows temporal overlap and what semantics this ordering might be based on. This issue also relates to BACM11-3 concerning entry and exit criteria for ValueStreamStages.
There is also a technical issue. UML allows for ordered associations. In practice these involve tagging links with an ordering value that is used to control the order in which links are iterated. This is also permitted in MOF. However, the actual ordering cannot be specified for the meta-model elements, only for their instances (which are the model classes).
One solution would be to add a property to the ValueStreamStage whose value controls the ordering. However, MOF properties are typically translated to OWL as DatatypeProperties and have semantic consequences for individuals. A better solution for OWL would be to define an AnnotationProperty that either orders ValueStreamStages directly or defines an ordering value. This implies a UML/MOF Comment attached to each ValueStreamStage, whose body contains a predefined keyword and an ordering value. Alternatively, a Comment could link to two ValueStreamStage instances and specify the ordering relation between them.

Define a non-semantic integer property for display ordering

Remove the ordered constraint from the owns association between a value stream and its stages. This is difficult to implement in OWL and requires the modeler to manage ordering constants that allow for placement of new value stream stages, the deletion of existing stages and the reordering of stages as the model is developed.
Add a property named presentation_order that is a static attribute (i.e. whose value is fixed for each class). When creating specializations of ValueStreamStage for a ValueStream, the modeler will assign integer initial values to this attribute for each specialization. Tools should use this value to define the presentation order. This property has no other semantic implications for the model.