GEMINI Allocation message — when is <DiagramNo> omitted?

[Deek]

We consume the GEMINI allocation Kafka feed and have noticed Allocation elements where <DiagramNo> is absent. The TAFTSI 5.3.1.GB / LINX XSD has DiagramNo as minOccurs="0" so it's schema-valid, but I haven't found anything documenting the operational rules.

Two questions:

1. Under what circumstances does GEMINI legitimately omit <DiagramNo> from an Allocation element? (e.g. early provisional allocation before a diagram is assigned, certain MessageStatus values, specific train types, etc.)
2. When a MessageStatus=2 (modification) message arrives without <DiagramNo> for a service that previously had one, should consumers treat this as:
   • the diagram has been removed from this allocation, or
   • the diagram is unchanged and just not re-stated in the modification?

For context — we're using (schedule_date, train_uid, diagram_no, resource_position) as a slot key to detect unit swaps, and the NULL-diagram cases break that logic.

Thanks

[Tom Cairns]

From memory a diagram number can be omitted when ad-hoc changes are being made particularly in significant disruption or very short notice alterations. We detect swaps just based on the change from the previous message on a service internally.

 

Note that resource position can be unreliable on some operators – as in some cases the data can be put purely in numerical (or alphabetical, depending on how you look at it) order.

 

Tom

 

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[Deek]

Many thanks Tom

Derek.